Microscopic
Anatomy
Laboratory Manual
2007
Department of Anatomy and Cell Biology
The George Washington University
Medical Center
Washington, D.C.
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Microscopic Anatomy
Laboratory Manual
© 2007 Kurt E. Johnson
All rights reserved. No part of this publication may be reproduced in any form without
prior written permission
Written, compiled and edited by Dr. Kurt E. Johnson. The editorial assistance of Drs.
Janette Krum, Louis DePalma, Kenna Peusner, Ann Chiaramello, and Mary Ann Stepp is
gratefully acknowledged. All illustrations not otherwise credited below them are either
original or taken from Kerr’s Atlas of Functional Histology under a site license.
Table of Contents
Preface
Epithelium and Glands
Nervous Tissue
Connective Tissue
Cartilage and Bone
Peripheral Blood
Bone Marrow and Hematopoiesis
Skin and Breast
Muscular Tissue
Lower Respiratory System
Cardiovascular System
Lower Digestive Tract I- Esophagus and Stomach
Lower Digestive Tract II-Small and Large Intestines
Liver, Gallbladder, and Pancreas
Immune System
Urinary System
Pituitary and Pineal Glands
Thyroid, Parathyroid, and Adrenal Glands
Eye and Ocular Adnexa
Auditory System
Female Reproductive System
Male Reproductive System
Upper Respiratory System
Upper Digestive Tract
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4
10
22
34
43
50
54
65
70
81
87
98
107
117
124
133
139
144
149
160
164
173
180
183
Preface
You are beginning a significant course of study toward becoming a physician. In
Microscopic Anatomy, we will be learning about the structure-function relationships in
cells, tissues, and organs that make up the normal human body. Understanding how a
particular biological structure is built will help you understand how it works. Conversely,
if you know how a tissue works, you should be able to describe at least rudimentary
morphological characteristics. For example, all cells dedicated to synthesis of proteins for
secretion from the cell have the following characteristics:
• Euchromatic nucleus with prominent nucleolus
• Prominent cytoplasmic basophilia due to an abundance of rough
endoplasmic reticulum
• A well-developed Golgi apparatus
• Membrane-bound vesicles containing secretion product
You will find this basic set of morphological characteristics in many different kinds of
cells. The table below lists some examples of cell types with this morphology, their
location in the body, and the function of the cell:
Cell Type
Motor neuron
Plasma cells
Acinar cell
Type II pneumocyte
Location
Spinal cord
Connective tissues
Pancreas
Lung
Function
Secretes neurotransmitter
Secretes antibodies
Secretes digestive enzymes
Secretes surfactant
Understanding this basic principle of the correlation between structure and function will
make it easier to learn to differentiate between the many different kinds of cells you will
encounter in your study of the microscopic anatomy of the human body.
You will also need to develop skills to distinguish organs that have similar
functions and similar structures. Organs can be maddeningly similar in appearance. One
of your important jobs in this course is to learn the similarities between organs with
similar functions and the differences that are reflections of subtle functional differences
between organs. For example, the uterine tubes can look surprisingly similar to the ductus
deferens. Both are conduits for gametes and have a lot of smooth muscle in their walls.
The uterine tubes are actively involved in transport of ova from the ovary to the uterus.
Their luminal epithelium is a simple columnar epithelium composed of a mixture of
ciliated and secretory cells. The cilia beat and propel ova toward the uterus. The secretory
cells secrete trophic substances that perhaps support early embryos and spermatozoa. The
ductus deferens propels spermatozoa downstream from the testis toward the penis. Their
luminal epithelium is a pseudostratified epithelium consisting of basal (stem) cells and
secretory cells.
We will begin the laboratory portion of this course by studying the four basic
tissues types, epithelium, connective tissue, muscular tissue, and nervous tissue. Then
we will study how these basic tissue types are assembled into organs. We will learn the
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microscopic anatomy of the major portions of important organ systems in the human
body. Learn structure-function correlates for each topic studied. This will give you a
conceptual framework to facilitate learning the complexities of cell, tissue, and organ
structure.
I have one other point to make in this Preface. My goal is to have each student
become a sophisticated microscopic anatomist. To accomplish this goal, you will need to
pay attention in class, read an atlas, follow directions in the manual, and spend as much
time as possible just looking at specimens. While you are struggling with trying to learn
the details, take time to appreciate the beauty of the cellular structures before you. Human
anatomy through the microscope is complex but if you become a sophisticated student of
this discipline, you will be rewarded with an appreciation of the beauty that lies beneath
this intricacy.
General Introduction
For each laboratory session, you will access a website on the Internet with a
digitized example of the appropriate slide. Once you have located the appropriate slide,
based on instruction in this manual, open that file, and look at the image at lowest
magnification. Try to familiarize yourself with the prominent landmarks of the slide, if it
indeed has such landmarks. In this manual, we will provide you with images of the files
with appropriate landmarks demarcated with arrows, letters, etc. Realize that some slides,
e.g., a blood film, will not have significant landmarks. We will indicate this in the
manual’s brief description of the slide. After you have located the appropriate file and
oriented yourself to its major landmarks, make an effort to imagine the three-dimensional
nature of the specimen. For example, if we show you a cross section of the uterine tube, it
will appear as a doughnut. Create a three-dimensional mental picture, based on “folk
anatomy” (early in the course), and what you have learned about the organ’s gross
anatomy from Gross Anatomy (later in the course). Then study the important features of
the specimen with the lowest magnification practical to accomplish the task at hand.
When you really need high magnification images, you will be directed appropriately in
the manual. You will rarely need to use high magnifications.
Be sure to bring an atlas with you to all laboratory sessions. By using this
manual, and an atlas, find structures as indicated in this manual. Follow the directions in
the manual carefully. This manual is designed as a step-by-step guide through each slide.
If you follow it carefully, you will have no difficulty finding indicated structures. Once
you have finished the basic drill outlined for each slide (in the manual), spend additional
time examining other features of the specimen, asking yourself questions about what you
see and providing answers to your questions by discussing the slide with colleagues or
faculty members.
Faculty members will be present during laboratory sessions. They are all experts
in this topic and can often help you figure out the slides, help answer your questions, and
perhaps pose new questions for thought and discussion. It is best to look at these slides
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during regular scheduled laboratory sessions because you will have access to expert
faculty help at that time. They are your best source of help in this laboratory. Also, don’t
hesitate to work closely with classmates who have previous experience or a gift for this
topic.
Specimen Preparation
There are several steps used in specimen preparation, usually performed in the
order below:
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Fixation-Fresh specimens are immersed in buffered solutions containing
aldehydes such as formaldehyde or glutaraldehyde. These fixatives kill cells,
arrest degenerative changes, and fix structures in a reasonable facsimile of living
cells.
Embedding-Aqueous fixatives are then washed away and replaced by organic
solvents, typically a series of aqueous solutions of increasing concentration of
ethanol, followed by an increasing concentration of alcoholic solutions of solvent
for embedding medium (e.g., xylene for paraffin). Once specimens are thoroughly
infiltrated with paraffin, they are put in small molds and oriented for sectioning.
The paraffin embedded specimen is then cooled to solidify the paraffin.
Sectioning-Embedded specimens are now mounted on a microtome, a device that
moves an embedded specimen forward a small (adjustable) distance, e.g.,10 μm,
over a sharp blade, producing a thin section (slice) of the embedded specimen.
Sections are then mounted on glass slides, deparaffinized, and rehydrated before
staining.
Staining-Stains increase the contrast of structures inside of the cells of the
specimens, facilitiating examination in the microscope. These are often mixtures
of several different dyes with differing affinities for structures in section (see
below). After staining, sections are covered with a thin glass coverslip. Now they
are ready for the microscope.
Computer-Glass slides of each specimen were then digitized and stored on a
server. You will access files through the server as thumbnails of entire specimens
with capability of examining defined optional areas of the specimen with optional
magnification.
Staining
Basic Dyes, e.g., hematoxylin or toluidine blue, are complex organic compounds
that absorb light (and thus solutions of them have a color). They have a net positive
charge and bind electrostatically to cell structures with compounds with a net negative
charge. For example, the DNA in the nuclear chromatin has many phosphate groups,
bears a net negative charge, and binds basic dyes (is basophilic or exhibits the property
of basophilia). Many of your slides have been stained with the basic dye hematoxylin
(the H of H&E stains).
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Acidic Dyes, e.g., eosin or orange G, are complex organic compounds that absorb
light (and thus solutions of them have a color). They have a net negative charge and bind
electrostatically to cell structures with compounds with a net positive charge. For
example, the collagen in CT has many positively chaged amino acids, bears a net positive
charge, and binds acidic dyes (is acidophilic or exhibits the property of acidophilia).
Many of your slides have been stained with the acidic dye eosin (the E of H&E stains).
Metachromasia-some basic dyes, e.g., toluidine blue, have a concentrationdependant absorption spectrum. Dilute solutions of toluidine blue are blue but
concentrated solutions are purple. Concentration-dependant shifts in the absorption
spectrum of the solution are due to interaction between electron clouds of adjacent dye
molecules, causing a shift in the absorption spectrum. When toluidine blue binds to fixed
macromolecules in specimens, it stains nuclear DNA blue but chondroitin sulfate in the
extracellular matrix (ECM) purple. In this instance, the nucleus is orthochromatic (blue)
(exhibits orthochromasia), while the ECM is metachromatic (purple) (exhibits
metachromasia).
Special Stains-only a few of our slides have stains other than H&E, i.e., special
stains. This lab manual will alert you to the use of a special stain when appropriate. There
are a host of these special stains but we will only be exposed to a few of them:
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Wright stain (similar to Giemsa stain)- a solution of several different dyes
commonly used to stain and differentiate formed elements of the peripheral blood
(in blood smears) or their precursors in bone marrow smears.
Elastic stain-a complex dye solution containing a dye that binds to the protein
elastin in elastic fibers, staining them a dark purple color.
Gold chloride-a heavy metallic gold ion in solution that precipitates reduced gold
(black) in some cells. Used for staining glial cells in nervous tissue.
Reticular fiber stain-a heavy metallic silver ion in solution that precipitates
reduced silver (black) on reticular fibers, staining them black
Mallory stain-a solution of several different dyes commonly used to stain
complex tissues. For example, in the pituitary gland, Mallory stain produces blue
basophils and orange-red acidophils.
Masson trichrome stain-a solution of three different dyes commonly used to
stain complex tissues. For example, in the gastroduodenal junction, Masson
trichrome stain produces red-purple nuclei, vermillion cytoplasm in smooth
muscle cells, and green in collagen fibers in CT.
Mallory stain-another complex dye solution, stains CT blue, nuclei purple, and
cytoplasm brick red.
Fontana Stain-a special stain using silver salts and a red counterstain. Reducing
substances such as granules in enteroendocrine (APUD) cells and collagen fibers
stain black (by causing deposition of silver metal) and cell nuclei stain red.
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Interpretation of a Three Dimensional Structure
from Two Dimensional Slices
When you first start looking at thin slices of complex organs, you will experience
some difficulty in making the extrapolation from the 2D view on your computer to a 3D
synthesis of the entire object. Examining pictures in a good atlas are quite helpful in this
regard, especially if the atlas has 3D diagrams of the overall structure of the organ. We
will illustrate some of the difficulties here with two simple examples. In the first
example, consider an egg. In this example, we will use an egg as a model of a cell. The
yolk of the egg will represent the cell’s nucleus and the white of an egg will represent the
cell’s cytoplasm. Look at section a below. If you pass a section through the middle of the
egg, parallel to the long axis of the egg, the yolk (nucleus) will appear in the middle of
the slice surrounded by white (cytoplasm). Section b still has white surrounding yolk but
section c has only white and no yolk at all. From this example, it should be clear that a
cell could appear to lack a nucleus if the plane of section passes through the cytoplasm
but misses the nucleus. If you pass sections perpendicular to sections a-c, you can also
obtain sections that miss the nucleus. Your job will be to appreciate the morphology of a
collection of cells by observing different representations (in different cells sectioned in
different planes) of similar or related objects.
Atlas of Functional Histology, ed. 10. © 2005 LWW, Philadelphia, pg. 5
Now lets examine a twisted epithelial tube cut in different planes. The ducts of
glands and convoluted tubules in the kidney both show some of this complexity.
Depending on the plane of section, you can have very different representations of the
same object, a twisted tube of simple cuboidal epithelial cells.
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Atlas of Functional Histology, ed. 10. © 2005 LWW, Philadelphia, pg. 5
How to Access and Use Digital Slides
1. Go to http://www.gwumc.edu/library/ and choose Students with left click. Under
Academics scroll down to • Histology Images and left click. This will take you
to a website called WebSlide® Virtual Slide Collection. Sets of slides are
arranged to correspond to your laboratory sessions. Our first formal laboratory
with be on Epithelium and Glands. Note that the first set of slides in the
collection is Epithelium and Glands. Use these for the first lab session.
2. Start by left clicking on Slide 17 and wait for image to load. You will see a
section with green borders. Move cursor to some area of interest inside the green
borders and left click. This will center image. Right clicking here will give you
magnification options. Choose a higher magnification by left click. By left
clicking and holding down, you can move around in specimen. Move to an area
of interest and release. You can center image at any time by positioning cursor
and then left clicking. Follow the text directions for this slide in your laboratory
manual.
3. Right clicking provides other options, including measuring distances and areas;
the system is automatically calibrated for different magnifications. To measure a
distance between A and B, right click and then select Tape Measure Mode with
left click. Now go to specimen, place cursor on A, hold left click and move to B
and then release left click. Distance in μm will automatically pop up. This
function is useful for measuring cell diamteres, thicknesses of layers, diameters
of tubular structures, and so forth. To shut off tape measure, right click, unselect
tape measure, and proceed. When you are done with a slide, just left click on the
next slide in the set and follow the directions in the lab manual.
4. The lab manual has thumbnail images of each specimen. Some of these are
labeled to help you find major structures and to get oriented to specimen. We
have not labeled everything that we want you to find because you will learn
about histological organization as you actively examine the specimens
searching for important structures as indicated in the lab manual. Atlases
have large collections of fully labeled diagrams and photomicrographs. Use these
in conjunction with your lab manual to become sophisticated microscopic
anatomists.
EPITHELIUM AND GLANDS
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Objectives
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Learn that epithelium is a boundary tissue with structural variations that serve
different functions
Learn to locate and identify the basic kinds of epithelium
Learn to locate and identify different types of glands
Be able to give an example of a location in the body where different kinds of
epithelium and glands are found
Overview
Epithelium
Epithelium is the first of the four basic tissue types that we will be studying. The
other three are connective tissue, muscular tissue, and nervous tissue. Epithelium is a
boundary tissue that covers free surfaces and lines cavities in the body. Epithelium has
the following characteristics:
• Apical surface is nonadhesive
• Rests on and firmly attached to a basement membrane (basal lamina)
• Has apical-basal polarization, e.g., basal nuclei and apical secretion
granules in some cells
• May have apical modifications, e.g., microvilli or cilia
• Avascular- no blood vessels in the epithelium proper. Oxygen and
nutrients diffuse to epithelium from blood vessels in the deep connective
tissues.
Epithelium comes in three major varieties, simple, pseudostratified, or
stratified. In a simple (one layered) epithelium, all cells rest on the basement membrane
and all cells contact the apical (free, luminal) surface. In a pseudostratified epithelium, all
cells rest on the basement membrane but not all cells reach the apical surface. In a
stratified epithelium, only some cells rest on the basement membrane and only some
reach the apical surface. The cells that make up an epithelium can vary in height. They
can be: thin (wider than tall) = squamous; approximately equal in width and height =
cuboidal; or narrower than tall = columnar. In stratified epithelia, the most apical cells
are used to name the epithelium. Thus, a single layer of flattened epithelial cells is a
simple squamous epithelium; whereas, several layers of cells with flattened apical cells
is a stratified squamous epithelium. A stratified squamous epithelium has basal cells
that are more or less cuboidal in shape, but, because the apical cells are flattened, it is
conventionally known as a stratified squamous epithelium. Transitional epithelium,
found only in the urinary tract, does not follow this simple schema. Transitional
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epithelium is stratified and has thick apical cells that bulge into the lumen. Some
epithelial layers are highly specialized and don’t fit neatly into this classification scheme.
For example, the seminiferous tubules in the testes have a complex mixture of tall simple
columnar epithelial cells with a proliferative, stratified epithelium between columnar
cells. The table below gives some examples of the different kinds of epithelium, where
they are found, and briefly describes the function of the epithelium:
EPITHELIAL CELL TYPES
Type
Simple squamous
Simple cuboidal
Simple columnar
Pseudostratified
Stratified squamous
Stratified cuboidal
Stratified columnar
Transitional
Other-Atypical
Example of Where Found
Lines cardiovascular system
Cortical kidney tubules
Small intestinal lumen
Lumen of seminal vesicles
Epidermis of skin
Lumen of sweat gland ducts
Lumen of male urethra
Lumen of urinary bladder
Lumen of seminiferous
epithelium
Function
Prevents blood clotting
Absorbs water and ions
Absorbs nutrients
Secretes part of ejaculate
Resists abrasion
Absorptive
Protective
Protects body from urine
Produces spermatozoa
Definitions of Terms Commonly Used in Discussions of Epithelium
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Apical- the superficial portion of an epithelium. It faces the free surface or the
lumen- opposite of basal.
Basal- the deep portion of an epithelium. It rests on the basement membraneopposite of apical.
Lumen- the hole or deep cavity in a tubular organ. The small intestine, blood
vessels, and the central nervous system all have a lumen. The lumen is a direct
result of the nonadhesive character of the apical surface epithelial cells
Endothelium- the simple squamous epithelium that lines the entire
cardiovascular system
Mesothelium- the simple squamous epithelium that lines the serous body cavities
(thoracic cavities, pericardial cavity, peritoneal cavity, tunica vaginalis testis
[surrounds testes-really an extension of the peritoneal cavity])
Glands
A gland is a collection of cells that secretes a substance either onto the surface of
the body (exocrine gland) or into the cardiovascular system (endocrine gland). Exocrine
glands contain secretory epithelial cells, supportive connective tissues, a blood supply,
and a duct that conveys secretions from the epithelial cells to the surface of the body
(skin, oral cavity, lumen of GI tract). Endocrine glands contain secretory cells, connective
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tissues, and a blood supply that receives the secretion. Individual cells that secrete a
product into a lumen are sometimes called unicellular glands, e.g., goblet cells secrete
mucus into the lumen of the respiratory system and GI tract.
Glands are classified by a standard system, depending upon the morphology of
the ducts and secretory units. If the duct is not branched, it is called a simple gland. If
the duct branches, it is called a compound gland. If the secretory portion is tubular, it is
called a tubular gland. If the secretory portion is expanded distally, it is called an alveolar
(acinar) gland. If the secretory portion is both tubular and alveolar, it is called a
tubuloalveolar gland. Most large exocrine glands (salivary glands, pancreas) are
compound tubuloalveolar glands. Furthermore, the individual secretory cells can either
be collected into serous alveoli (= acini), i.e., they secrete a protein-rich secretion
product; or mucous alveoli (= acini), i.e., they secrete a mucus-rich secretion product.
The cells of serous alveoli have a round basal nucleus, extensive basal cytoplasmic
basophilia, and a collection of darkly stained apical granules of stored secretion product.
The cells of mucous alveoli have a more basal, flattened nucleus, and a massive store of
apical droplets of mucus. In H&E preparations, protein-rich granules stain darkly but
mucus-rich granules do not stain at all. The parotid salivary glands and the exocrine
pancreas have predominantly serous alveoli. The sublingual salivary gland has
predominantly mucous alveoli. The submandibular salivary glands and the tracheal
glands are mixed glands with both serous and mucous alveoli.
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Slide 17. Artery, Vein, and Nerve, Hematoxylin and
Eosin (H&E)
The entire cardiovascular system is lined by a simple squamous epithelium called an
endothelium. The term endothelium applies only to the simple squamous epithelium that
lines the cardiovascular system. It is one cell layer thick (simple) and the cells are
flattened (squamous). Individual endothelial cells look more or less like a fried egg. The
yolk would be the nucleus and the white would be the cytoplasm. Now imagine cutting
the fried egg in a plane perpendicular to the fry pan. If you looked at the cut edge of the
fried egg, you would see a central flattened yolk (nucleus) surrounded by white
(cytoplasm) and a thin layer of white extending outward from the yolk to the edge of the
egg.
This specimen is a cross section cut perpendicular to the long axis of an artery, vein, and
nerve. At low magnification, you will notice two irregular (collapsed) blood vessels, a
vein (V) and an artery (A) and a sectioned nerve (N). Each has a pink wall and a lumen
filled with red blood cells that are stained bright red. The large blood vessels are
surrounded by a foamy mass of adipose tissue (fat) and other connective tissue that
bundles the three related structures together. Locate the lumen of the artery (or vein),
increase the magnification, and notice that the cells at the edge of the lumen have
flattened, purple nuclei. These are the nuclei of individual endothelial cells. These cells
are exceedingly flat so that often the cytoplasm is so attenuated that it not visible without
the aid of an electron microscope. The basement membrane of this epithelium is quite
thin and can’t be identified with precision. Furthermore, immediately deep to the
basement membrane of the endothelium, you will find collagen fibers and fibroblasts of
the wall of the blood vessel. You will not find a distinct location where the endothelium
ends and the surrounding connective tissue begins. If you had an electron microscope,
you could clearly view the endothelial cell cytoplasm, the endothelial basement
membrane (the boundary between the epithelium and the surrounding connective tissue),
and the collagen fibers of the CT. Do not try to study the other tissues at this point. Just
use this slide to find an example of simple squamous epithelium and then press on to
the next slide. We will come back to this slide later to study its CT, nerve (N), and other
details.
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Slide 38, Lung, H&E
Serous body cavities, e.g., the thoracic or peritoneal cavities, are lined by another kind of
simple squamous epithelium called mesothelium. The mesothelium has its apical
surface facing into the serous cavity. The organ filling the cavity (lung in thoracic cavity)
is covered on one side by the visceral pleura with the apical surface of the mesothelium
facing into the thoracic cavity and the corresponding parietal pleura, attached to the
body wall with is mesothelium facing apically toward the thoracic cavity, so that the
organ does not stick to the body wall but slides freely past it during breathing. Examine
this cut block of tissue, removed from the surface of the lung and then sectioned. Three of
the edges are cut edges and are straight. The fourth edge is curved (on the left side) and
represents the natural anatomical surface of the lung. It is covered by the visceral pleura
(VP), the most superficial layer of which is a simple squamous epithelium called
mesothelium. The mesothelium may be damaged or missing (an artifact) but as you scan
along this surface, you should be able to find some flattened purple nuclei. Thoracic
surgeons can also damage the mesothelium during surgery and this may cause painful
adhesions of the lungs to the body wall. A bronchus (B) and a pulmonary artery is also
visible in the specimen. See if you can find the endothelium at the lumen of the
pulmonary artery. The bronchus is a passive conduit that carries air from the trachea to
small, sac-like alveoli in the distal reaches of the lungs. Gas exchange occurs in the
alveoli. The pulmonary artery carries deoxygenated blood from the heart to the alveoli,
where gas exchange oxygenates the blood.
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Slide 63, Infant Kidney, H&E
This is a slice from the kidney of an infant. The convex, curved portion is the natural
anatomical surface of the kidney. The irregular space contains the lumen (L) of a calyx
(collects urine from the renal tubules and conveys it to the ureter) and some adipose
tissue filling the renal sinus. The kidney has a superficial cortex (C) and a deep medulla
(M). In the cortex you should be able to find numerous tubules lined by a simple
cuboidal epithelium. Here you will find cells that are approximately as tall as they are
wide. After satisfying yourself that you can find simple cuboidal epithelium, look more
carefully at the acidophilic (pinker) cortical tubules with an irregular lumen. You may be
able to locate the apical brush border here, consisting of “lawns” of microvilli. These
are proximal convoluted tubules. The function of these epithelial cells is predominantly
transport luminal materials out of the lumen. The microvilli increase the cell surface area
available for this transport. Now look in the medulla. Here you will be able to find more
tubules lined by simple cuboidal epithelium (thick limbs of loops of Henle and collecting
tubules) as well as tubules lined by simple squamous epithelium. Those with red blood
cells in lumina are capillaries. Those without red blood cells in lumina are thin limbs of
loop of Henle. Don’t be concerned at this point about all of the complex structural details
of the kidney. Simply use this slide to learn to identify different kinds of epithelium. We
will revisit this slide later in the course when we study the urinary system.
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Slide 66, Gallbladder, H&E
This is a curved section of the gallbladder. The concave surface faces on the lumen (L) of
the gallbladder. This surface is lined by a simple columnar epithelium. Once you locate
the luminal epithelium, increase the magnification to find a single layer of cells that are
taller than they are wide. The chief function of this epithelium is the absorption of water
from bile stored in the lumen (L) and prevention of bile constituents from diffusing out of
the gallbladder. Once again, don’t spend a lot of time studying the intricacies of the
gallbladder; we will come back to it. Just find good examples of simple columnar
epithelium and press on.
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Slide 51, Duodenum, H&E
This is a cross section through a part of the wall of the duodenum, the first part of the
small intestines. The lumen (L) of the small intestine contains partially digested food.
There is also a small portion of the pancreas (P) adjacent to the duodenum. Adjacent to
the lumen you will find a simple columnar epithelium consisting of mostly tall
columnar absorptive cells and a few goblet cells. Both are part of the luminal
epithelium. The absorptive cells have numerous apical microvilli. These cells are
dedicated to absorption of digested nutrients. The goblet cells secrete mucus which coats
and protects the epithelium from digestive enzymes secreted into the lumen via a duct
(not shown) of the pancreas. At the bases of villi, there are deep surface invaginations
called Brunner glands. These are coiled tubular glands that secrete bicarbonate (to
neutralize stomach acids) and mucus (to protect the lining of the duodenum). The
pancreas is an example of the compound tubuloalveolar gland. The alveoli (acini) of the
pancreas contain serous cells that secrete digestive enzymes. In the pancreas, look for
ducts in the connective tissues between acini and lobules. These will be lined by several
different kinds of epithelium including simple cuboidal and simple columnar.
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Slide 37, Trachea, H&E
The trachea is a hollow tube that passes through the chest, conveying air to and from the
nasopharynx and the lungs. There are two specimens on this slide. One is straight with
three centrally placed pink oval structures in it. The pink structures are sections through
C-shaped rings of hyaline cartilage (a specialized connective tissue) that have significant
flexibility and elasticity. They keep the lumen of the trachea patent during swallowing
and movement of the neck so that air can pass from the nasopharynx to the lungs. This is
one half of the wall of the tubular trachea, cut parallel to the long axis of the tube. The
other section is curved with fewer than three pink structures in the middle. This is a cut
perpendicular to the long axis of the trachea. The concave side is the luminal (L) surface,
which is lined by a pseudostratified, ciliated, columnar epithelium with goblet cells.
This pseudostratified epithelium has all cells resting on the basement membrane, but not
all cells reaching the luminal (apical) surface. For example, you will be able to find short,
round, darkly stained cells resting on the basement membrane. These basal cells are a
stem cell population that contains dividing cells. After mitosis (cell division), one
daughter cell remains behind on the basement membrane and persists as a stem cell. The
other differentiates into a ciliated cell, goblet cell, or other cell types found in the
epithelium. The ciliated cells span the entire thickness of the epithelium and have
numerous apical cilia. Cilia beat continuously, propelling a film of mucus up the trachea,
proximally, away from the lungs. These surface appendages have an array of
microtubules arranged as 9 peripheral pairs surrounding a central pair (visible only in the
electron microscope). Goblet cells have an apex distended by mucus and a basal nucleus.
You may also be able to see examples of compound tubuloalveolar glands (G) and
their ducts deep to the epithelium. These mixed glands have serous alveoli (secreting
protein-rich materials) and mucous alveoli (secreting mucus-rich materials) that coat and
protect the luminal surface of the trachea.
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Slide 49, Esophagus, H&E
The esophagus is a tube that conveys swallowed food from the oropharynx to the
stomach. At low magnification, you can see a bright pink wall, consisting mostly of
several layers of muscular tissue (the muscularis externa (ME)). This muscular tissue
contracts to propel food down the esophagus, toward the stomach. At the lumen (L),
there is a wavy purple layer called the mucosa. All moist visceral organs have a mucosa
at the lumen. The mucosa consists of a superficial epithelium, a connective tissue
domain (called the lamina propria), and a thin layer of smooth muscle fibers called the
muscularis mucosae. In the esophagus, the mucosal epithelium is a stratified squamous
unkeratinized epithelium. Whenever you identified a stratified squamous
epithelium, be sure to specify whether or not it is keratinized. In general, dry
stratified squamous epithelia are keratinized and moist stratified squamous epithelia are
unkeratinized. The esophageal mucosal epithelium is multilayer (stratified), with
flattened (squamous) apical cells with nuclei (unkeratinized). The function of this
epithelium is to resist the abrasion of semi-solid food as it passes through the lumen. We
will discuss keratinized epithelia further when we examine the next slide. Notice that
although quite thick, the esophageal mucosal epithelium is nevertheless avascular. Its
blood supply is found in the lamina propria. Do not try to learn all of the anatomical
details of the esophagus, just learn how to identify stratified squamous unkeratinizied
epithelium and find mixed compound tubuloalveolar glands in the deep connective
tissues of the mucosa and deeper connective tissues.
19
Slide 26, Thick Skin, H&E
This semicircular specimen is a section through the thick skin from the palms of the
hands or the soles of the feet. Skin has a superficial epithelium called epidermis (thin
purple curved superficial layer) (E) and a deep connective tissue called dermis (D) (thick
pink layer deep to epidermis). The epidermis is an example of a stratified squamous
keratinized epithelium. It is multilayered (stratified), the superficial cells are flattened
(squamous), and there are many superficial layers of dead, dried, non-nucleated
(keratinized) cells. The epidermis is resistant to abrasion. Keratinization is a complex
cellular process whereby cells in the basal layer of the epithelium divide and then
accumulate a store of a hydrophobic protein called keratin, dying and loosing their
nuclei as they do so. Stratified squamous keratinized epithelium resists abrasion and
prevents desiccation.
20
Slide 64, Ureter, H&E
This is a cross section of the ureter, a small tubular organ that conveys urine from the
kidneys to the urinary bladder. It is somewhat flattened and the lumen (L) is compressed.
The mucosal epithelium in the ureter is an example of transitional epithelium, also
found in the renal calyces, renal pelvis, urinary bladder, and proximal urethra (and
nowhere else in the body). Examine the luminal epithelium at higher power. You will
notice a stratified epithelium. The apical cells are quite thick and often have rounded
apices that project into the lumen. These cells are often described as “pillowy.” This is a
good place to recall that a stratified epithelium as classified based on the morphology of
the most apical layer of cells. Therefore, it would not be correct to classify this as a
stratified squamous epithelium. The epithelium is stratified (has several layers) but the
apical cells are thick and rounded rather than squamous. Transitional epithelium
functions to protect underlying tissues from urine. The urinary bladder fills with urine
and then empties periodically. As the volume of the bladder increases, its inner surface
area increases rapidly (as a cubic function of the radius). The transitional epithelium of
the empty bladder is many cell layers thick and the apical cells are particularly thick and
round. As the bladder fills, the epithelial cells are stretched and become more flattened.
In addition, the number of epithelial cell layers decreases as the surface area occupied by
the epithelium increases. This is a unique feature of transitional epithelium.
21
NERVOUS TISSUE
Objectives
•
•
•
•
Learn to recognize parts of a neuron: cell body (soma) with and without axons
and dendrites, axons with and without myelin, sensory receptors, and motor
end plates and know their functions.
Distinguish between CNS and PNS neurons
Learn to identify different kinds of glial cells and know their functions. You
should be able to find the following glia:
In CNS—
Astrocytes
Oligodendroglia
Microglia
Ependymal cells (and choroid plexus epithelium)
In PNS—
Satellite cells
Schwann cells
Learn the basic histological organization of a gross peripheral nerve; be able to
identify fascicles and myelinated axons (nerve fibers). Identify perineurium,
epineurium, and endoneurium and learn to distinguish the nuclei of
endoneurial fibroblasts and Schwann cells. Nodes of Ranvier should be
identified histologically and understood physiologically.
Overview
The nervous system is specialized for communication. It conveys information-rich
sensory signals from the peripheral receptors to the brain and sends motor responses
from the brain to the peripheral organs. Nervous tissue is the second of the four basic
types of tissue. The other three types are epithelium, connective tissue, and muscular
tissue. Nervous tissue is, in fact, a highly modified version of epithelial tissue. The CNS
begins as a simple tubular pseudostratified epithelial structure. Many features of
epithelial tissues persist in the central nervous system. For example, it retains an apical to
basal polarization. Apical tight junctions join the apical borders of cells of the CNS, may
have cilia, and face on a lumen (brain ventricles and central canal of spinal cord). The
outer boundary of the CNS is its basement membrane.
The nervous system is composed of two basic subdivisions: the central nervous
system (CNS) (brain and spinal cord) and everything else: the peripheral nervous system
(PNS) (peripheral nerves, sensory and motor, dorsal root ganglia, and the sympathetic
and parasympathetic division of the autonomic nervous system.
22
Nervous tissue contains two broad classes of cells: neurons and glia. All cells in the
nervous system are either neurons or glia by definition. Neurons are specialized cells that
communicate. There are about 1,000,000,000,000 (one trillion, 1012) neurons in the brain
alone. All the rest of the nonneuronal cells in the nervous system (not including blood
vessels and cells) are glial cells by definition. They outnumber neurons about 10:1 in the
CNS, so there are approximately 10,000,000,000,000 (ten trillion, 1013) glia in the brain.
Glial cells are nonneuronal cells. They have special functions including production of
myelin, forming boundaries between neurons, removal of debris after neuronal injury or
death, production of cerebrospinal fluid, and uptake of excess K+ from the extracellular
space for homeostasis.
In the CNS, we speak of gray matter and white matter. Fresh or fixed specimens of
the brain and spinal cord are generally light (white or gray) because they have myelin
everywhere. White matter and gross nerves is a pearly white because they are covered by
myelin. Areas called gray matter have plenty of myelin but also have abundant neuronal
cell bodies. These impart a grayish cast on an otherwise white tissue. So, for example, the
spinal cord has a butterfly-shaped central gray area because here there are many neuronal
cell bodies (in the sensory and motor horns) and a peripheral surround of white matter
because here there are mainly myelinated fiber tracts and relatively few neuron cell
bodies.
Slide 1, Spinal Cord, H&E
This slide is a cross section of the spinal cord. The dorsal (D) (posterior, back) and
ventral (V) (anterior, belly) surfaces of the spinal cord are labeled. The darker, central,
“butterfly-shaped” gray matter and the lighter, peripheral white matter are visible.
Portions of two sensory nerves enter the spinal cord on both dorsal sides. A single motor
nerve exits the spinal cord on the left side of the section. Notice that there is a deeper
fissure in the middle of the ventral surface. This is the ventral median fissure. In most
cross sections of the spinal cord, the ventral median fissure is a reliable marker for the
ventral surface, helping to distinguish the ventral (anterior, motor) horn from the dorsal
(posterior, sensory) horn. Once you are oriented to this slide, find the large motor
neurons in the ventral horns. These have a multiploar cell body (soma) with a single
23
axon and several dendrites. They have large, euchromatic nuclei with a prominent
nucleolus. The cytoplasm is filled with basophilic granules. This is the Nissl substance,
which consists of aggregates of rough endoplasmic reticulum. Motor neurons are some
of the largest cells in the body. Their cell bodies are enormous and their axons arise from
the soma and project out of the spinal cord in the ventral root, ending on a motor end
plate on a peripheral skeletal muscle. These axons can be up to a meter long, beginning in
the spinal cord and extending in the leg to the muscles in the foot. Now locate a sensory
horn and find sensory neurons. They are similar to motor neurons but smaller. Now
move out to the white matter. Here you will see numerous small nuclei of mostly glia
cells. Take a few minutes to see if you can identify three broad classes of glial cells:
Astrocytes—with the larger, round, more euchromatic nuclei
Oligodendrocytes—with the smaller, round, more heterochromatic nuclei
Microglial cells—with the smaller, fusiform or irregularly shaped, most
heterochromatic nuclei
Finally, in the middle of the slide you will find a small, round lumen. This is the central
canal of the spinal cord. Facing the lumen you will see some low columnar epithelial
cells. These are ependymal cells, a fourth kind of glial cell on this slide. What is the
name of the liquid filling the central canal?
Slide MS_LO5_087, Spinal Cord, Cervical, Rat. KlüverBarrera Stain
This is a cross section of the spinal cord stained with a combination of basic dye cresyl
violet and other dyes. This dye has a net positive charge and binds to negatively charged
macromolecules in the section, e.g., nucleic acids. You can see the deep ventral median
fissure and the ventral motor horn (vh). Find a large motor neuron in the motor horn and
observe its large soma, large nucleus, prominent nucleolus, and Nissl substance.
Outside the ventral horn, you can see tracts of nerve fibers running perpendicular (up and
down the spinal cord) to the plane of this section of the cervical spinal cord.
24
Slide 33, Cerebral Cortex, Gold Chloride Stain
This is a section of a piece of the cerebral cortex. It has two large gyri (arrows)
(prominent rounded elevations on surface of the brain) separated by a deep sulcus (S)
(furrows on the surface of the brain). You can also see cortical gray matter (GM) and
white matter (WM) deep to it. You think, “I’m confused, didn’t they just tell us that the
spinal cord has deep gray matter and superficial white matter.” Yes we did. So does the
brain. There are deep nuclei in the brain (gray matter)—not shown on this slide. White
matter contains many myelinated fibers that connect these deep nuclei to a second layer
of gray matter in the superficial cortex of the brain. So, the spinal cord has deep gray
surrounded by superficial white and the brain has deep gray, surrounded by intermediate
white, surrounded by superficial gray matter. The cortical gray matter allows us to
speak, think, learn, create, emote, and remember
Use this slide to study astrocytes. Astrocyte processes reduce gold ions to gold metal
(black) and cause it to be deposited within them. In this section, at high magnification,
you will see that astrocytes are the black stained glial cells with multiple processes
radiating away from the cell body. Neurons are not stained at all, only a subset of the
astrocytes. You can also see long black channels. These are small brain blood vessels.
Notice how astrocyte processes are associated closely with these vessels. How might they
function?
Now scan along the surface of a gyrus. Notice how the processes of the astrocytes appear
to aggregate together to form a thin black layer as the boundary of the brain. This is
called the glia limitans. Lets try to make a subtle and therefore challenging distinction.
You can also see that the astrocytes of white matter have a finer array of processes. They
look “fuzzier.” These are called fibrous astrocytes. In contrast, in the gray matter, the
astrocytes have fewer processes and a more robust, “meatier” cell body. These are
protoplasmic astrocytes.
25
Slide 16, Peripheral Nerve Longitudinal and Cross
Sections, H&E
This slide contains two sections of peripheral nerve, one longitudinal (LS) on the left and
the other a cross section on the right. Start with the cross section at low power. Notice
that it consists of several large bundles called fasicles (f). A connective tissue capsule
called the epineurium (e) surrounds the entire gross nerve. Branches of the epineurium
called the perineurium surround functionally related groups of axons called fasicles (f).
Now go to high magnification and wander around deep in any fascicle. You can see
numerous eosinophilic (pink) axons surrounded by a “foamy” myelin sheath. These are
individual nerve fibers. Fibers are bundled together by collagen fibers and fibroblasts that
constitute the endoneurium. There are also numerous capillaries in the endoneurium.
There are basically three kinds of nuclei present here:
1) Nuclei of capillary endothelium
2) Nuclei of endoneurial fibroblasts
3) Nuclei of Schwann cells
The first two kinds of nuclei are quite similar, being flattened and darkly stained. The
endothelial nuclei are at the edges of capillaries and are concave with respect to the
capillary lumen (filled with RBCs). The nuclei of endoneurial fibroblasts are between
capillaries and myelin sheaths. You will be able to find good example of both but will not
be able to unequivocally identify all nuclei. The nuclei of Schwann cells are rounder,
fatter, and less darkly stained. They are concave with respect to the myelin sheath and
axon. These PNS glial cells wrap around axons to form the myelin sheath.
26
Slide UF037B, Nerve, c.s. + l.s., Rat, Toluidine Blue
This slide shows nodes of Ranvier in the longitudinal section (ls) in the upper right. Find
an area where the nerve fibers are relatively straight. Now, at high magnification, look at
the nerve fiber. You can see long, thin light blue lines (axons) surrounded by parallel
tracts of darker blue material (the myelin sheath). The myelin is mostly lipid and is wellfixed in this slide. As you travel along an axon, you will find areas where the myelin
sheath disappears and reappears. These are nodes of Ranvier, locations where one
Schwann cell ends and another begins. Think of a wire pushed through the center of a
length of sausage links. After threading the wire through the chain of sausage links, use a
knife to cut the links apart and push the links away from one another to create small
spaces between them. You would be left with a wire, mostly covered by sausage but
exposed at the cuts. In this model, the wire is the axon, the sausage links are the
Schwann cells, and the gaps between sausage links are the nodes of Ranvier. Nodes of
Ranvier are easily found in this slide. Your will also be able to find nuclei of endoneurial
fibroblasts, Schwann cells, and endothelial cells lining small blood vessels.
27
Slide MCW 207, Dorsal Root Ganglion, H&E
The (purple) dorsal root ganglion receives signals from peripheral receptors and passes
them on to the spinal cord. The dorsal root ganglion contains large (up to 100 μm) and
small (15-25μm) neuron cell bodies pushed out the edge of the ganglion. The nuclei of
these neurons are more or less centrally placed in the cell body. These are unipolar
neurons with a single process that splits into two branches, a dendrite carrying sensory
information to the cell body from peripheral receptors and an axon conveying sensory
information away from the cell body toward the spinal cord. A thin layer of satellite
cells, a type of neuroglia, surrounds each cell body. Scattered throughout this DRG you
can find many myelinated nerve fibers. Do Schwann cells or oligodendroglia form this
myelin? Explain your answer!
28
Slide LH 0064, Autonomic Ganglion, H&E
This autonomic ganglion has many nerve fibers connection multipolar neurons. You will
be able to find the cell bodies of these neurons easily in the area marked CB. Autonomic
ganglia have many uniform (15-45 μm) multipolar cell bodies, in contrast to the last
slide, where we looked at unipolar neurons of two classes, large and small. In autonomic
ganglia, the cell bodies are more multipolar because of their numerous dendrites.
Satellite cells form an incomplete border around the neuron cell bodies. The neuron cell
bodies have nuclei that are more eccentric than in the DRG, and their cytoplasm has
many small brownish granules of lipofuscin. This lipid-rich pigment is accumulated
residues of lysosomal digestion and increases with age.
29
Slide 61, Jejunum, Fontana Stain
This slide shows the autonomic innervation of the gastrointestinal tract quite well. First,
look between the inner (ime) and outer layers of the muscularis externa (ome). You
will find large round structures, ganglia (collections of neuron cell bodies), surrounded by
black fibers. You can also see small nerve fibers connecting the ganglia. This is the
myenteric (Auerbach) plexus. Now move toward the lumen of the organ (top of slide)
and find the folded, thin layer of smooth muscle called the muscularis mucosae.
Between the muscularis mucosae and the ime, there is a submucosal layer of CT. Just
deep to the muscularis mucosae, in the most superficial part of the submucosa, you will
find isolated neuronal cell bodies or small groups of 2-3 cell bodies. These are parts of
the submucosal (Meissner) plexus. These are parasympathetic neurons.
Slide 26, Thick Skin, H&E
This slide of thick skin has peripheral sensory receptors, including Meissner corpuscles in
the dermal papillae (dp) and a pacinian corpuscle located at pc in the dermis. The
Meissner corpuscle has a group of supportive cells that surround a sensory nerve fiber. If
30
you find a dermal papilla with cells in the core that are aligned perpendicular to the long
axis of the papilla, these are probably supportive cells of a Meissner. The Meissner
corpuscle subserves the sense of light touch in the skin. The nerve ending is not visible.
A good example of a Meissner corpuscle is shown below:
An example of a Meissner corpuscle in dermal papilla
If you cruise on down to the area labeled pc, you will find a nice example of a pacinian
corpuscle. It has a free nerve ending surrounded by many concentric layers of supportive
CT cells. In section, it looks much like a cut edge of an onion. Pacinian corpuscles are
found in the dermis and hypodermis (and curiously in the pancreas) and are the deep
pressure sensors. A good example of a pacinian corpuscle is shown below:
31
An example of a pacinian corpuscle in the pancreas, similar
to those found in dermis and hypodermis
Motor End Plates (no slide)
Motor neurons in the ventral (anterior) motor horns have long axons that exit the
spinal cord and travel along motor roots, where they eventually innervate skeletal
muscles. The termination of a motor nerve fiber on a skeletal muscle is a synapse-like
structure called the motor end plate. Motor impulses cause release of vesicles of
acetylcholine from the presynaptic membrane into the synaptic cleft. The postsynaptic
membrane (the sarcolemma) has acetylcholine receptors that cause muscle contraction
when loaded with acetylcholine. An example of a group of motor end plates is shown
below:
32
MEP = motor end plate; N = nerve; smf = skeletal
muscle fiber
33
CONNECTIVE TISSUE (CT)
Objectives
•
•
•
•
•
Learn the basic classification system for connective tissues
Learn to identify and distinguish different kinds of CT
Know where different kinds of CT are found in the body
Understand the kinds of cells, fibers, and amorphous ground substances found in
CT
Learn to identify resident CT cells, e.g., fibroblasts and adipocytes and immigrant
CT cells, e.g., plasma cells, macrophages, eosinophils, and lymphocytes.
Overview
Connective tissue (CT) is the third basic tissue type. We will be focused on CT
for the next three lab sessions. As their name implies, most CTs join things together. For
example, muscles are attached to bones by CT tendons. All CTs are invariably composed
of three essential components:
•
•
•
Cells
Fibers
Amorphous Ground Substance
The fibers and amorphous ground substance collectively form the extracellular
matrix (ECM). The extreme differences in properties of different CTs are due to
different combinations of properties of constituents. For example, blood is an unusual
liquid CT with many red and white cells and a liquid ECM. The fibers are potential
fibers in solution (fibrinogen) that only become actual fibers (fibrin) when blood clots
into a gelatinous semisolid. On the other end of the spectrum, we have concrete-like CT
in bone. Here, the ECM is filled with crystallized calcium salts. Tendons have many
collagen fibers arranged parallel to one another like strands in a rope, for tensile strength.
One commonly used schema for classification of adult CTs is shown below
Connective tissues proper
General
Loose (areolar)
Hypodermis, mesenteries, omentum, and lamina propria
Dense Irregular
Dermis, periosteum, organ capsules
Dense Regular
Tendons, ligaments
Special
Adipose tissue
Reticular tissue
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Cartilage
Bone
Blood
Slide 8, Loose (Areolar) Connective Tissue Spread,
H&E and elastic fiber stain
The tissue in this slide is an example of loose CT (areolar CT). Areolar CT is widely
distributed throughout the body. It fills the spaces between organs and holds them
together. After dissection from an area surrounding an organ, we spread it on a slide and
stained it with H&E and a dye that binds specifically to elastic fibers. Hematoxylin stains
cell nuclei faintly blue/purple, eosin stains collagen fibers pink, and the elastic stain
imparts a dark black/purple color to elastic fibers. Use this slide ONLY to appreciate the
random distribution of cells and fibers in loose CT. You should not try to identify
individual cells here. You should also observe that the cells and fibers are relatively
sparse, when compared with dense CTs, and are thus called loose CT.
35
Slide 52, Jejunum, H&E
This is a cross section through the wall of the jejunum, the longest portion of the small
intestines. In this slide, examine loose CT in the lamina propria. To find lamina propria,
find the lumen (L) of the jejunum and then increase magnification. Villi project into the
lumen. Villi are covered by a simple columnar epithelium as the most superficial layer
facing the lumen. Just deep to the epithelium, there is a mucosal CT domain called
lamina propria, forming the core of villi. This loose CT has numerous fibroblasts with
long, thin nuclei oriented parallel to the long axis of the villus. These are resident cells of
the lamina propria. In addition, you will be able to find immigrant cells, e.g.,
eosinophils, plasma cells, and lymphocytes. These cells move into and out of the lamina
propria via capillaries as needed. Eosinophils have two or three purple nuclear lobes and
numerous bright red cytoplasmic granules. Plasma cells have a single round nucleus with
light purple euchromatin and dark purple heterochromatin arranged in blobs on the edge
of the nucleus, creating a “cartwheel” appearance. There is a thick layer of basophilic
(purple) cytoplasm surrounding the nucleus of the plasma cell. Lymphocytes have a
small, round, heterochromatinized (dark purple) nucleus and only a thin, scarcely visible
shell of cytoplasm around the nucleus.
Euchromatin = uncondensed chromatin, lightly stained, functionally active
Heterochromatin = condensed chromatin, darkly stained, functionally inactive
Basophilia = binding a basic dye (hematoxylin), has net negative charge (in case of
plasma cell, due to cytoplasmic ribosomes, rich in RNA
36
Slide 77, Junction between pyloric stomach and
duodenum, Masson Trichrome
This is a section through the point where the pyloric stomach (PS) joins the first part of
the small intestines, the duodenum (D). All GI organs have four basic layers, starting at
the lumen they are:
• MUCOSA = surface epithelium + lamina propria + muscularis mucosae
• SUBMUCOSA = dense irregular CT between mucosa and muscularis externa
• MUSCULARIS EXTERNA = thick, multilayered muscular layer
• ADVENTITIA = thin CT capsule of organ
The wall of the gastrointestinal tract has much layered smooth muscle called the
muscularis externa (ME). Notice this striking thickening of the muscularis externa
between the pyloric stomach and the duodenum. This is the pyloric sphincter. The lumen
of the GI tract is at the bottom of the slide. You can easily see the mucosa and deep to it,
the green layer between the mucosa and the muscularis externa. This is the submucosa.
Use this slide to study the abundance and distribution of (green) collagen fibers in the
lamina propria, submucosa, muscularis externa, and adventitia. Do not try to identify
individual cell types in the lamina propria.
37
Slide 38, Lung, H&E
Starting just beneath the visceral pleura (VP), locate the foamy tissue. There are thinwalled alveoli everywhere. Inside the alveoli, look for pulmonary macrophages. These
are large ovoid cells with an irregular border, an irregular nucleus, and prominent black
specks in the cytoplasm. These pulmonary macrophages are important immigrant CT
cells. They can pass easily from the blood, through pulmonary capillaries, across the
epithelium lining the alveoli, and onto the surface of the alveoli. Once in alveoli, these
cells ingest (phagocytose) bacteria, molds, inorganic and organic particulate matter, etc.
and remove it from the lungs by reversing their entry path. They can enter the CT
domains that surround alveoli where they may deposit their load of particulate matter. In
interalveolar CT, you can find black deposits. These have been cleared from the alveoli
and deposited there as a result of the activity of pulmonary macrophages. Pulmonary
macrophages are part of a complex system of dedicated phagocytes called the
mononuclear phagocyte system, which includes blood monocytes, fixed and mobile
macrophages (in immune organs), Kupffer cells (in liver), osteoclasts, microglia (in
CNS), and others.
38
Slide 17, Artery, Vein, Nerve, H&E
In this slide, loose CT and adipose tissue surround the artery (A), vein (V), and nerve
(N). The primary cell of most adipose tissue is the unilocular (one fat vacuole) adipocyte.
Sections of these cells resemble a signet ring. They have a large central vacuole of fat.
The solvents used to prepare the slides extract the fat, so the vacuoles are empty. There is
also a thin shell of cytoplasm surrounding the vacuole. On one thicker side of the cell, the
cytoplasm contains a nucleus. CT fibroblasts can be converted into adipocytes, leading to
an accumulation of adipose tissue. Adipose tissue functions as anatomical “packing
material” (e.g., around the eyeball and kidneys), and serves as a storage reservoir for
excess caloric intake. In times of caloric excess, adipose tissue stores energy-rich lipids
for consumption in times of caloric deficit. Chronic caloric excess leads inevitably to
weight gain by accumulation of adipose tissue. Notice how many capillaries (minute red
spaces) are associated with the adipose tissue. Miles of capillaries supply the (sometimes)
hundreds of pounds of adipose tissue that accumulate in obese patients, leading to a
drastic increase in peripheral vascular resistance. No wonder obese patients also
commonly have hypertension (high blood pressure).
39
Slide 26, Thick Skin, H&E
Look in the dermis (D) for an example of dense irregular CT. Here, the CT is called
dense because it has more cells and fibers per unit volume (when compared to loose CT)
and irregular because the cells and fibers form overlapping bundles running in many
different directions. Study the arrangement of pink (mostly collagen) fibers and the
purple fibroblast nuclei. This section is stained with H&E so the elastic fibers that are
also scattered among the collagen fibers are not easily identified. The deeper portions of
the section (at the bottom) also contain some subcutaneous adipose tissue. By way of
review, find a blood vessel and locate its luminal endothelium. What kind of epithelium
is it? What kind of epithelium is found in the epidermis (E)?
Slide 9, Muscle-Tendon Junction, H&E
This is a thin (2μm) plastic section of a muscle-tendon junction. The skeletal muscle (M)
is darker pink (bottom) and the tendon (T) is lighter pink (top). A tendon is an example of
40
a dense regular CT. It consists of numerous collagen fibers with fibroblasts (with long,
thin, purple nuclei) between them. There are many cells and fibers/unit volume (dense)
and cells and fibers are arranged parallel to one another in a regular array. The fibers are
aggregates of long collagen molecules bound side-to-side and end-to-end, giving tendons
enormous tensile strength.
Slide 25, Lymph Node and Liver, Reticulum Stain
This slide has two sections, a lymph node (LN) and a piece of liver (L). This specimen
has been specially treated with a reticulum stain, which demonstrates thin, black
reticular fibers. These are abundant in the spleen, lymph nodes, bone marrow, and liver.
They form a supportive CT meshwork to support the organs. Reticular fibers have an
abundance of type III collagen and are rich in carbohydrates. The carbohydrates reduce
silver ions in the stain, causing deposition of silver metal on reticular fibers, thus staining
them black.
Slide 35, Auricle (Pinna), Elastic Stain
This is a section of the auricle (pinna) of the outer ear. It has been stained with orcein, a
dye that reacts strongly with elastic fibers. The serpentine, dark purple structure in the
middle of the slide is a piece of elastic cartilage (EC), a specialized CT with numerous
elastic fibers. Locate the cartilage and then at high magnification, observe the numerous,
41
thin, purple-black mats of elastic fibers. You can also find them in the dermis of the thin
skin that covers the auricle and in the walls of blood vessels.
Slide 30, Aorta, Elastic Stain
This is a section through the wall of the aorta. This is the main blood vessel that carries
high-pressure blood out of the left ventricle into the systemic circulation. Looking
anywhere in the wall, observe green collagen fibers, yellow smooth muscle cells,
brownish-red elastic fibers. The wall of the aorta consists of many fenestrated elastic
laminae sandwiched between layers of collagen fibers and smooth muscle. These
laminae are very much like concentrically arranged tubes of rubber with holes punched in
the walls. The aorta balloons out slightly when high-pressure blood is ejected from the
left ventricle. Then elastic recoil of the wall of the aorta propels the blood along. Patients
with congenital abnormalities in certain CT proteins (e.g., Marfan syndrome) or older
patients can have life-threatening aortic aneurysms (ruptures).
Lamina, (pl. laminae) = a layer (plywood is laminated)
Fenestration = from the Latin word for window (fenestra) a hole in a layer, the wall of a
building can have fenestrations (windows), or a layer (lamina) of elastic fibers can have
holes, we speak of one fenestrated elastic lamina or two f. e. laminae.
42
CARTILAGE AND BONE
Objectives
•
•
•
Learn to identify the three types of cartilage and give examples of where they are
found in the body
Learn the microscopic anatomy of both bone and cartilage and understand their
similarities and differences
Understand the different modes of bone formation
Overview
Cartilage and bone are specialized skeletal connective tissues. Because of special
properties of their extracellular matrix, they can serve as semi-rigid (cartilage) or rigid
(bone) structural elements that give shape to the body and enable gross movements of
parts of the body, powered by contraction of skeletal muscles. Cartilage and bone are
living, metabolically active supportive structures. Bone in particular is constantly being
remodeled and is capable of extensive repair (following fracture). One of bone’s most
remarkable characteristics is that it is constantly being destroyed and rebuilt anew, all the
while maintaining its basic morphology and structural integrity. The first kind of cartilage
we will study, hyaline cartilage, not only provides flexible support for the trachea and
bronchi, but also covers the articular surfaces of many long bones, and forms the skeleton
of the embryo. Embryonic hyaline cartilages are the immediate precursors of most the
bones of the axial (base of skull, vertebrae) and appendicular (upper limbs, shoulder
girdle, lower limps, pelvic girdle) skeleton.
Slide 37, Trachea, H&E
There are two different planes of section through the trachea, longitudinal on the left and
cross on the right. Each has large pink masses of hyaline cartilage (HC) in them. At low
43
magnification, locate a hyaline cartilage. Notice that there are no blood vessels in the
hyaline cartilage proper. In general, cartilage is avascular. The perichondrium is a dense
CT capsule that surrounds the cartilage. The outer part of the perichondrium consists of
fibroblasts that grade off indistinctly into surrounding CTs. Now proceed to a higher
magnification and gradually move deeper into the hyaline cartilage, away from the
capsule. Notice that the cells of the flattened perichondrial fibroblasts gradually become
fatter and surrounded by more extracellular matrix (ECM). Fibroblasts of the superficial
perichondrium differentiate into chondroblasts. These secrete ECM of hyaline cartilage,
mostly collagen fibers and an amorphous ground substance of cartilage proteoglycan.
As chondroblasts secrete ECM, they become entrapped in their own secretions. Once
ECM surrounds chondroblasts, they are chondrocytes by definition. Chondrocytes
occupy cavities in the ECM called lacunae. Imagine a block of Swiss cheese. It consists
of cheese (ECM of cartilage) and holes. Put a grape in each hole. Now make a slice of
the block of cheese with inserted grapes. You will now have slices of cheese (cartilage
ECM), holes (lacunae), and slices of grapes (chondrocytes). Chondrocytes often have
large central fat vacuoles where they store nutrients. When organic solvents used in tissue
preparation dehydrated the trachea, the lipids in the vacuoles were extracted and the
chondrocytes collapsed into the lacunae.
Slide 47, Epiglottis, Elastic Stain
The epiglottis is a flexible flap of tissue covering the orifice of the larynx in your throat.
It prevents ingested food from entering the respiratory system. When you talk, a reflex
lifts the epiglottis up to allow air to exit the respiratory system. When you swallow, a
reflex seals the orifice of the respiratory system. When you talk and eat simultaneously,
food can be aspirated, causing choking and coughing. There is a large bar of elastic
cartilage (EC) running down the middle of the epiglottis. In an H&E preparation, hyaline
cartilage and elastic cartilage are nearly identical. However, if special stains are used to
reveal elastic fibers, elastic cartilage has many more elastic fibers (dark purple-black).
Look at the blood vessels. They also have elastic fibers in their walls. Where else might
you find elastic cartilage? Identify the epithelial coverings on both surfaces of the
epiglottis.
44
Slide AE_A28, Fibrocartilage, Mammal, H&E
This slide has an excellent example of the third kind of cartilage, fibrocartilage (fc),
which joins two pieces of bone. Examine the fibrocartilage at 10X. You can see many
light purple strands of densely-packed collagen fibers running in several different
directions. There are also small clusters of 3-5 chondrocytes nestled between the
collagen fibers. At 40X, you can see the nuclei of chondrocytes, chondrocyte lacunae,
and a small field of darker purple cartilaginous extracellular matrix surrounding
chondrocyte lacunae. Minute collagen fibers are also visible in the bundles of collagen
running between nests of chondrocytes.
Slide 6, Intervertebral Disc, H&E
Between each vertebra, there is an intervertebral disc (IVD). This section has a part of
one vertebral body with a shell of compact bone (CB) on the outside and a marrow cavity
(MC) on the inside. The intervertebral disc has a dense CT capsule of fibrocartilage
called the anulus fibrosus and a semi-liquid central core called the nucleus pulposus.
Examine the intervertebral disc near the vertebral body to be sure that you are in the
anulus fibrosus. Here you will find fibrocartilage, the third kind of cartilage. It looks
45
much like the dense regular CT of a tendon but here and there you will find small clusters
of chondrocytes with a small amount of cartilage matrix surrounding then. Traumatic
tears in the anulus fibrosus combined with compression can lead to extrusion of the
nucleus pulposus (herniated or ruptured disc). The herniated, semi-liquid nucleus
pulposus can rest on spinal nerves, usually causing pain, numbness, and loss of motor
function. Why is the most common site of a herniated disc at the L4/5 level?
Slide 3, Bone Ground to Thin Slice, India Ink
(otherwise unstained)
This is a fragment of a long bone (e.g., the humerus) cut perpendicular to the long axis of
the bone. The fragment has then been ground down to a thin slice and flooded with India
ink to fill all the holes with black material. The inorganic matrix is still present but soft
tissues have been lost. No cells are visible. Many haversian systems (osteons) are
present. Look almost anywhere in the slide at intermediate power. Once you have found a
haversian system that looks like the atlas, increase the magnification. Use this specimen
to locate haversian canals, lamella of bone, osteocyte lacunae, and canaliculi. The
haversian canals are the largest, round or oval holes. Blood vessels occupy the center of
the haversian canals. Notice that a few layers of concentrically arranged haversian
lamellae surround them. Each lamella has “spidery” holes in it. The holes are osteocyte
lacunae and the minute black projections radiating away from the lacunae are canaliculi.
In life, these lacunae are occupied by osteocytes and the canaliculi contain osteocyte
processes. Notice that you can start at a haversian canal and meander through the
canaliculi to the edge of the haversian system. This diffusion pathway is how nutrients
and oxygen get from the blood vessel in the haversian canal out to the peripheral
osteocytes of the haversian system. You might encounter a Volkmann canal, a vascular
channel that cuts across lamellae rather than running parallel to lamella (haversian
canals). Finally, between haversian systems, you will find small collections of polygonal
lamellae. These are interstitial lamella. They are remnants of old, degraded haversian
systems used to cement haversian lamella together. The free anatomical surfaces of the
gross bone (not in slide) will have circumferential lamellae following the external
surface of the bone and along the inner surface of the bone, adjacent to the marrow
cavity.
46
Slide 4, Rib Bone, Cross Section, H&E
This is a decalcified rib that has been sectioned perpendicular to the rib and stained. Use
this slide to appreciate the difference between the outer shell of compact bone (CB) and
the inner mass spongy (cancellous) bone (SB). There is a periosteum covering the outer
surface of the bone. Superficially, it consists of flattened fibroblasts but as you move into
the compact bone, you may be able to see fatter osteoblasts. When they secrete osteoid
(uncalcified ECM of bone) and this becomes calcified, the osteoblasts become
osteocytes. You will be able to find osteocytes in lacunae but the lamella are less
evident. Trabeculae project from the compact bone to form spongy bone. The
endosteum is a discontinuous layer of osteoblasts that covers the inner surface of the
compact bony and all of the trabculae of the spongy bone. In the large spaces between
trabeculae of spongy bone, there are blood vessels and a marrow compartment with
hematopoietic stem cells forming different stages of red and white blood cells.
47
Slide 5, Parietal Bone, H&E
This is a section of the parietal bone, one of the flat bones making up the calvaria, the
upper, dome-like vault of the skull. This kind of bone has two thin layers of compact
bone sandwiching a thin layer of spongy bone. The spongy bone is called the diploë.
The parietal bone is curved to accommodate the brain. This arch of bone is light and
strong, affording protection to the brain. The bones of the calvaria and some facial bones
form spontaneously in embryonic mesenchyme (a loose CT of embryos), by
intramembranous ossification Here, fibroblasts differentiate into osteoblasts and these
cells secrete osteoid, which calcifies to form plates of bony tissue. After birth, these
plates fuse to form the rigid protective calvaria of the skull. Before birth, the bones of the
calvaria are mobile, allowing compression of the skull during passage through the birth
canal.
Slide 7, Developing Bone, H&E
The three sections on this slide are from left to right, perpendicular to the long axis of the
hand at the level of carpal bones, perpendicular to the long axis of the hand at the level of
metacarpal bones, and parallel to the long axis of a digit. The tip of the digit is at the top.
Two and one half phalanges are included in the section. Use this slide to study different
stages of endochondral ossification. Articulations between the distal phalange and the
48
middle phalange as well as between the middle phalange and the proximal phalange are
easily found. Study the carpal and metacarpal “bones.” These are hyaline cartilaginous
models of the carpal and metacarpal bones. In them, you will be able to find
perichondrium, chondroblasts, and chondrocytes. Finally, locate the developing bone
(DB) in the right-most section. In the middle of this bone, you will find a bony collar.
Now proceed to either end of the developing bone, locate the hyaline cartilage, and then
at high magnification, slowly scan along the cartilage, away from the articular surface, to
find:
Resting zone -chondrocytes evenly spaced
Proliferation zone – chondrocytes pushed together, mitotic figures present
Hypertrophy zone- at edge of bony collar, chondrocytes expanding, large
lacunae
Calcification zone- purple spicules and trabeculae of calcified cartilage
Bone- same color as bony collar
Using your atlas and its diagrams, reconstruct the processes involved in endochondral
ossification. Tell your neighbor how to convert a fragment of hyaline cartilage into a
gross bone. What is the significance of the epiphyseal plate in the bone of a growing
child? If you look inside the marrow cavity of the developing bone, you will also find
excellent examples of osteoclasts. These are large, multinucleated cells with an
eosinophilic cytoplasm pressed directly against the endosteum. As they degrade bone,
they create hollowed-out depressions in the surface of the bone (Howship lacunae).
Where do embryonic remnants of hyaline cartilage persist in the long bone of a
prepubertal child or of a postpubertal adult?
49
PERIPHERAL BLOOD
Objectives
•
•
Learn how to identify all of the cells and formed elements of peripheral blood.
Do a differential blood count to determine the frequency of all of the formed
cellular elements of blood (not counting platelets).
Overview
Blood is a specialized liquid connective tissue. It contains cells (red and white
blood cells), formed elements (platelets), potential fibers (fibrinogen), and an amorphous
ground substance of proteins and glycoproteins (plasma). In an adult, there are
approximately 5 L of blood (slightly more on average in a male and slightly less in a
female, related mostly to differences in volume). The cells include red blood cells
(RBCs), white blood cells (WBCs, leucocytes in five flavors), as well as cellular
fragments called platelets (for clotting).
When blood is drawn and sedimented by centrifugation, the erythrocytes settle to
the bottom of the tube. The leucocytes and platelets form a thin pale band called the
buffy coat on top of the pellet of RBCs. The supernatant is the plasma. The RBCs
occupy about 45% of the volume (the hematocrit), the buffy coat is about 1%, and the
rest is supernatant. Plasma contains albumin, globulins, fibrinogen, thrombin, transferrin,
and other blood proteins. During clotting, fibrinogen reacts with thrombin to form fibrous
polymers of fibrin. Platelets then adhere to the fibrin to form a clot. The plasma residue
after clotting is called serum.
For studying cell morphology of peripheral blood, by a differential blood count, a
drop of blood is placed on a slide and spread out into a smear. The smears are then dried
and stained with dye mixtures (e.g., Wright stain or Giemsa stain). In favorable regions of
the smear, you can find an evenly distributed, well-stained sample of peripheral blood.
Please Note: Your lab manual has good examples of all of
the cell types that we will want you to be able to identify.
To view these images in color, go to the version of the lab
manual on Blackboard.
50
Slide 13, Peripheral Blood Smear, Wright Stain
Under low magnification, scan the slide to find an area where cells are well-stained and
closely packed but not clumped. Use an atlas to help you locate each cell type. First find
an erythrocyte (obvious) and note its diameter. This slide only allows a maximum
magnification of 40X but you can still use it to identify all of the common cells in the
peripheral blood.
Use the erythrocyte as a benchmark to determine the diameter of leucocytes. The small
purple speck in the middle of the micrograph above (at the arrow) is a platelet. You will
find them everywhere in your specimen. They may also be clumped in small groups.
Caution: As you search for different kinds of leucocytes, be aware that some cells
have been destroyed by the smearing technique or may be poorly stained. Blobs of
stain can look misleadingly like cells. Don’t spend time on the artifactual
“trashocytes.” Use your pictures and atlas for help in identifying leucocytes. Now find a
nucleated cell and answer four questions in this order:
•
•
•
•
What is cell’s diameter (use the RBC as a “ruler”)
What is the cell’s nuclear morphology? Round? Curved blob? Lobated? How
many lobes?
What are characteristics of cytoplasm? Granular or agranular?
If granular, are granules minute and grayish (neutrophil), large and bright red
(eosinophil), or large and bright purple/red (basophil)
Slide UW007, Peripheral Blood Smear, Wright Stain
This slide has a 63X function with it, so if you want to look more carefully at the
cytological characteristics of the different leucocytes, scan this slide. You will probably
most easily find a leucocyte like the one shown below:
51
•
•
•
•
Its diameter is about 14 μm, approximately twice that of an RBC.
Its nucleus has 3-5 lobes.
Its cytoplasm is faintly granular with gray granules.
This is a neutrophil, the most abundant leucocyte.
The table below summarizes the morphological characteristics of the cells and formed
elements of peripheral blood.
#/mm3
(% of
WBCs)
5X106
Nucleus
Specific
Granules
Wright stain look,
special features
Function
None
None
O2/CO2 transport
10-12 μm
5,500
(≅55%)
3-5 lobes
Small,
gray
Eosinophil
12 μm
2-3 lobes
Large, red
Basophil
10 μm
300
(≅3%)
100
(≅1%)
2-3 lobes
Large,
purple
Monocyte
13-17μm
500
(≅5%)
Indented
None
Lymphocyte
7-12 μm
3,500
(≅35%)
Round
None
Platelet
2-3 μm
200,000
None
Granulomere
Red/orange,
biconcave disc
Blue/gray
cytoplasm, minute
granules
Bluer nucleus,
granules obvious
Purple granules,
often lying over
nucleus
Lots of cytoplasm,
indented, palestaining nucleus
Little or no
cytoplasm, dense,
round nucleus
Small, irregular,
often clumped
Cell
Diameter
in films
Erythrocyte
7-9 μm
Neutrophil
Phagocytosis
bacteria
of
Combats parasites
Allergic reactions
Phagocytosis
Immunity
Coagulation
Now repeat this drill for each leucocyte that you encounter. The next most abundant (and
therefore next most easily found) leucocyte is a lymphocyte:
52
Note that its diameter is more like 9 μm, its nucleus is round, and its agranular cytoplasm
forms only a thin shell around the nucleus.
By searching different areas systematically, you should be able to find many monocytes:
A few eosinophils:
53
And perhaps even a basophil. These cells are scarce. You will recognize them by their
diameter, bi-lobed nucleus, and large purple granules. Don’t spend a lot of time looking
for an example on the slides. A good example of a basophil from your slide is shown
below:
Neutrophil on the left and basophil on the right
Somebody will find one during the lab session and have a look at it. Rather than focusing
on this rare cell, spend you time learning to recognize the other cell types and then
perform a differential count by identifying 100 leucocytes and keeping a record of the
relative frequency of them. How do your results compare with those in the table above?
BONE MARROW AND HEMATOPOIESIS
Objectives
•
•
•
Learn basic histology of bone marrow, especially the relationship between the
endosteum, vascular space, and marrow compartment.
Identify and learn major stages of erythropoiesis and granulopoiesis
By the end of the lab period, we expect you to be able to identify megakaryocytes,
primitive
stem
cells,
proerythroblasts,
basophilic
erythroblasts,
polychromatophilic erythroblasts, orthochromatophilic erythroblasts, myeloblasts,
promyelocytes, myelocytes, metamyelocytes, and bands.
Overview
The internal (marrow) cavity of many long bones is supported by trabeculae of
spongy bone. Most marrow in an adult is a loose CT massively infiltrated with
adipocytes. There are many blood vessels. This yellow marrow is not hematopoietically
active. In a few places (e.g., vertebral bodies, the iliac crest, the sternum), hematopoietic
stem cells outnumber adipocytes and we find red marrow. The marrow compartment is
54
found in spongy bone in the space between the endosteum (a layer of bone-lining cells as
well as osteoblasts on the trabculae) and the vascular endothelium. Capillaries of bone
marrow (aka sinusoids) are continuous sheet of endothelial cells, joined together by tight
junctions. They are continuous but form transient apertures that allow passage of mature
blood cells from the marrow compartment into the systemic circulation.
Bone marrow contains many different stages of hematopoiesis from the most
primitive pluripotent stem cells, to erythroid precursors, granulocyte precursors, and
mature cells. An overview of the different commitment points for differentiation of the
cells and formed elements of blood is shown in the diagram below on the next page.
Bone marrow can be studies in three kinds of preparations:
•
•
•
Histological sections of bones stained with H&E are used to study bone
architecture and to define the relationship between trabeculae of spongy
bone, the endosteum, the vascular sinusoids, and the marrow
compartment.
For clinical diagnosis, bone marrow aspirates are obtained by entering the
marrow cavity (e.g., at the ilac crest or sternum) with a stylet, removal of
bone marrow with a sterile syringe, and the smearing bone marrow cells
on a slide and staining cells with Wright stain.
When it is important to study cytoarchitecture of marrow, a larger stylet is
inserted into a bone, and a cutting tool removed a core biopsy, which
includes bone and marrow. The core biopsy is then used to make touch
preparations and is embedded and sectioned to study cytoarchitecture
The diagram below shows the “family tree” of hematopoiesis. The pluripotent
hematopoietic stem cell can form either a lymphoid stem cell (precursor of lymphocytes)
or a myeloid stem cell (precursor of all of the other cells and formed elements of the
peripheral blood).
55
56
Slide 15, Bone Marrow Section, Giemsa Stain
This is a section through a typical bone. It shows intact marrow (purple masses) between
bony trabeculae (pink wavy lines). Scan this preparation at low magnification and note
fragments of bony trabeculae, vascular channels (sinusoids, containing RBCs), and
clusters of hematopoietic cells in the marrow proper. Learn to distinguish between
endothelial cells lining sinusoids and the adipocytes of marrow. Hint: The lumen of
sinusoids will be filled by RBCs.
57
Slide 4, Rib Bone, Cross Section, H&E
Scan this slide in the spongy bone (SB) at low magnification and learn the relationship
between bone trabeculae, vascular channels, and the marrow compartment. The largest
cells in the marrow compartment are megakaryocytes. What is their fate?
Slide 14, Bone Marrow Smear, Wright Stain
You will spend the rest of the lab session on this slide. Look around at low magnification
for an area with numerous, well-spread, well-stained, undamaged cells. Many cells will
be damaged by smearing or poorly stained. Do not try to identify these artifacts. You
will find many different developmental stages. It is not always possible, even for
experienced hematologists, to unequivocally identify every cell. The IDs of many cells
are debatable. Do not try to identify every cell. Instead, guided by an atlas, start with the
erythroid series and try to sort out clear examples of different stages. Use the same drill
that you used to identify cells in the peripheral blood smear. For each cell that you want
to identify:
(1) Determine its diameter, using the RBC as a benchmark
(2) Locate its nucleus. Now characterize its lobulation, chromatin distribution,
presence or absence of nucleoli, etc.
(3) Identify notable cytoplasmic characteristics. Is the cytoplasm basophilic?
Granular or agranular? If granular, are granules azurophilic, neutrophilic,
eosinophilic, or basophilic?
Use the cytoplasm of the RBC to establish an eosinophilic reference point and then
characterize other structures as azurophilic, basophilic, or eosinophilic accordingly. Here
are some approximate indicators of the frequency of cells encountered in a typical smear
from the marrow of a normal adult:
58
•
Granulocyte precursors
(collectively) about 2:1
•
Granulocyte Series
Myeloblasts 2%
Promyelocytes 5%
Myelocytes 12 %
Metamyelocytes 42%
•
Erythroid series 20-30%
•
•
•
•
Lymphocytes 10-20%
Plasma cells 2-5%
Monocytes < 1%
Megakaryocytes <1%
(collectively)
outnumber
erythrocyte
precursors
Now begin to identify specific cells. In this exercise, it will be helpful to focus up and
down as you look at individual cells. To get your feet wet, start with the
megakaryocyte. This is the largest cell seen in the smear. It has a diameter of 100-200
μm (note its huge size in comparison to clumps of erythrocytes and surrounding myeloid
cells). It also has a purple cytoplasm and a large, segmented nucleus with extensive
heterochromatin. The megakaryocyte fragments in the bone marrow, releasing platelets
into the circulation. In the picture below, there is a cluster of dozens of platelets in the
top center.
59
Now find an area with numerous small RBC-like cells with dark, round, eccentric nuclei.
This is a cluster of cells of the erythroid series. Look around the group and at neighboring
cells comparing the tinctorial characteristics of the cytoplasm to surrounding
erythrocytes. Identify the following cells:
Note: To aid in your search, we have included photographs taken from the same slides
used for the computer images. These images are in the color version of the Lab Manual
on Blackboard. You can also consult an atlas.
Basophilic erythroblast
•
•
•
•
•
15-20 μm diameter
Large, round, heterochromatic nucleus and no nucleolus
Cytoplasm very blue, agranular
Mitotic
Distinguish from the rare proerythroblast which is slightly larger and has a
nucleolus
60
Two basophilic erythroblasts
Polychromatophilic erythroblast
•
•
•
•
10 μm diameter
Round, extensively heterochromatic nucleus, no nucleoli
Cytoplasm agranular, less blue than above
Mitotic
Three polychromatophilic erythroblasts
Orthochromatophilic erythroblast
•
•
•
•
Diameter only slightly larger than RBC
Nucleus small, round, completely heterochromatinized, eccentric in cell
Cytoplasm same color at RBC
Postmitotic
61
Orthochromatophilic erythroblast
Reticulocytes and erythrocytes are similar in Wright-stained smears, although
reticulocytes are slightly larger and are more blue-gray. Using special stains,
reticulocytes are easily identified:
The cells with dark inclusions are reticulocytes
Now wade into the granulocyte series. Your instructors realize that you are still
novices here so we don’t expect you to be able to do this easily or quickly.
Furthermore, many of the cells are transitional stages that cannot be unequivocally
identified. Work hard at this and don’t get frustrated. Work diligently and
systematically, making frequent reference to pictures in your atlas.
Basically, the myeloblast, which lacks cytoplasmic granules, accumulates nonspecific
(primary) azurophilic granules to become a promyelocyte. Once specific (secondary),
neutrophilic, eosinophilic, or basophilic granules first become evident, the cell is called a
myelocyte. Now, specific granules accumulate in the cytoplasm and the cell’s nucleus
becomes deeply indented and then lobate. At this point, the cell is called a
metamyelocyte. These come in three flavors, as do the mature granulocytes of peripheral
blood, namely neutrophilic metamyelocytes (with neutrophilic granules), eosinophilic
metamyelocytes (with eosinophilic granules), and basophilic metamyelocytes (with
basophilic granules). Here are the myeloid cells you should be able to find:
62
Myeloblast
•
•
•
•
•
14-18 μm cell diameter
Large round nucleus with 2 or more nucleoli
Agranular, basophilic cytoplasm
Mitotic
Two myeloblasts
Promyelocyte
•
•
•
•
20-25μm cell diameter
Large irregular nucleus with several nucleoli
Azurophilic (large, reddish purple) granules
Mitotic
Promyelocyte
63
Myelocyte
•
•
•
•
15-20 μm cell diameter
Nucleus indented on one side, more heterochromatic than promyelocyte, no
nucleolus
Azurophilic and specific (neutrophilic [minute, gray], eosinophilic [large, red], or
basophilic [large, dark purple]) granules
Mitotic
Top cell is a neutrophilic myelocyte
Metamyelocyte
•
•
•
•
12-15 μm cell diameter
Nucleus heterochromatic, indented, no nucleoli
Cytoplasm now dominated by specific granules
Postmitotic
Neutrophilic band
The early metamyelocyte has a slightly indented nucleus, usually curved or indented
deeply. Later, more mature cells have 2 lobes (neutrophilic bands) and 3-5 lobes when
completely mature. Bands for eosinophils and basophils are not evident. Instead, the
mature eosinophils and basophils commonly have 2 lobes.
64
SKIN AND BREAST
Objectives
•
•
•
•
Learn to identify different types of skin
Learn to identify appendages and glands associated with skin
Learn to identify the layers of the epidermis and relate these layers to the
process of keratinization
Learn to identify different functional states of mammary glands
Overview
The skin covers the entire outer surface of the body. It consists of a stratified
squamous keratinized epithelium called the epidermis and a dense, irregular connective
tissue called the dermis. The skin protects the outer surface of the body, preventing
invasion by external microorganisms and loss of internal fluids. The sweat glands and
sebaceous glands are surface invaginations of the epidermis. The former produces a
dilute salt solution for cooling the body. The latter produces a lipid-rich skin conditioner.
Hair follicles protect and decorate the skin. The skin also has a rich sensory innervation.
Mammary glands are modified sweat glands present in both sexes, although more
functionally developed in females, where, under the influence of ovarian and pituitary
hormones, they grow into a secondary sexual characteristic during puberty and produce
milk after pregnancy. They produce a complex secretion called milk, used for infant
nutrition. Milk is rich in lipids, proteins, carbohydrates, vitamins, and generic and
specific antibacterial substances. It serves as a complete food supply and protects against
enteric pathogens for the early growth and development of a young human being.
65
Slide 26, Thick Skin, H&E
This is a histological section of thick skin. Thick skin is found on the soles of the feet and
the palms of the hands. Note that it is hairless. The two main components of the skin are
the epidermis (E) and the dermis (D). Using low magnification, beginning at the
epidermal-dermal junction, you can see an irregular boundary. The cone-shaped dermal
projections are called dermal papillae. They form the superficial papillary layer of the
dermis, which also has a deep reticular layer. Deep to that, one can see the hypodermis
with abundant adipose tissue. Now increase magnification and study the epidermis. This
is a classic example of a stratified, squamous, keratinized epithelium. The deepest layer
of the epidermis is the stratum basale (s. germinativum). It rests on a robust basement
membrane that forms the epidermal-dermal boundary. Now moving more superficially,
locate the stratum spinosum, s. granulosum, s. lucidum, and s. corneum. These layers
represent different stages in the differentiation of keratinocytes. You should also use this
slide to locate eccrine sweat glands deep in the dermis and their ducts as they project
toward the surface of the epidermis. Meissner corpuscles (light touch) can be found in
the papillae and a single pacinian corpuscle (PC) (deep pressure) is in the upper left
edge of the specimen, near the dermal-hypodermal boundary. What role do desmosomes
and hemi-desmosomes play in epidermal integrity? Epidermal-dermal adhesion? Name
two functions of dermal papillae? Can you distinguish different cell types in the secretory
portion of sweat glands? How do the secretory portions compare to the ducts?
66
Slide 27, Thin Skin, H&E
This is a specimen of thin skin. It has a few hair follicles with associated arrector pili
muscles and sebaceous glands, and a much thinner s. corneum when compared to the
last slide. Dermal papillae (dp) are more prominent than in thick skin and the dermis is
denser. Otherwise, it is quite similar to thick skin. Review the layers of the epidermis,
paying particular attention to the s. basale. The nucleus of each cell has a cap of dark
pigment (melanin) granules. These organelles are secreted from melanocytes (not
visible) and pass into cells of the s. basale. Melanin is a protein particularly rich in amino
acids with cyclic hydrocarbon side chains. Melanin absorbs mutagenic (carcinogenic),
solar, ultraviolet radiation. Basal cell carcinomas and malignant melanomas are
uncommon in dark-skinned individuals and more common in light-skinned individuals,
due in part to the protection offered by cutaneous melanin. See if you can find a hair
follicle, a sebaceous gland, and some sweat glands. Hair follicles are more abundant on
the next slide. Observe the relative thickness of the s. corneum here and in the last slide.
Where would you find thin skin?
Slide 32, Scalp, H&E
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This is a specimen of the scalp, thin skin with numerous hair follicles. The roots (deep
purple ovals) of hair follicles (rhf) are anchored in the hypodermis. Using your atlas,
locate dermal papillae, external and internal root sheaths, and the shaft of the hair.
The sections of hair shafts are not attached directly to the internal root sheath in the more
superficial parts of the hair follicle and may have been displaced (or are missing) by
sectioning artifact. In the more superficial dermis there are numerous sweat glands and
sebaceous glands. The hair follicles are deep surface invaginations of the epidermis.
There most basal cells are quite similar to the s. basale in thick skin. The other layers in
the hair follicle are similar to the layers of the rest of the epidermis. Indeed, flakes of
dead skin and hairs are chiefly keratin. Notice that sebaceous glands have ducts that
empty into the hair follicle. What is the function of sebum? You should also be able to
find arrector pili muscles. These are slips of smooth muscle fibers oriented at an oblique
angle to the hair follicle. What is their function?
The mammary glands are compound, tubuloalveolar, highly modified sweat glands. They
are present in both male and female mammals. In female mammals, the mammary glands
hypertrophy during lactation but involute extensively when not in use for infant nutrition.
In contrast, in human females, they develop in two phases, first as part of puberty and
second during pregnancy. They probably serve as sexual attractants and certainly serve
as a source of nutrients for infants. We will study both nonlactating and lactating
mammary glands from sexually mature human females.
Slide 95, Nonlactating Mammary Gland, H&E
The alveoli (a) of this gland are functionally inactive. A connective tissue (ct) domain
surrounds them. This specimen is about 50% alveoli and 50% connective tissue. There is
a fair amount of adipose tissue in the CT domain. Observe the alveoli and ducts of the
glandular component.
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Slide 94, Lactating Mammary Gland, H&E
This is a thin plastic section of a lactating mammary gland. The alveoli (a) (purple)
represent about 90% of the whole specimen, with CT (pink) occupying the rest of the
space. In the secretory alveoli, there is a simple cuboidal epithelium and a few alveoli
are dilated with eosinophilic stored milk. See if you can identify myoepithelial cells
surrounding the alveoli. What is their function? How do the ducts differ from the alveoli?
Can you find adipose tissue? Eventually, you will need to be able to distinguish this
tissue from thyroid gland, salivary glands, and prostate gland. For example, the lactating
mammary gland, especially when most of the alveoli are filled with milk, can look almost
identical to the thyroid gland. However, the mammary gland is an exocrine gland and has
ducts, whereas the thyroid gland is an endocrine gland and therefore lacks exocrine ducts.
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MUSCULAR TISSUE
Objectives
•
•
•
•
To be able to identify all three types of muscular tissue
To be able to distinguish between skeletal muscle and dense regular CT
To be able to distinguish between smooth muscle and surrounding irregular CT
To relate morphological differences between three kinds of muscle fibers to their
innervation and functional properties.
Overview
Nearly all cells have at least some intrinsic motility based on actin-myosin systems.
Muscle cells (= muscle fibers) have unusually large amounts of these contractile proteins
to meet their motility specialization. Smooth muscle fibers have plenty of actin and
myosin, but these contractile proteins are not organized into sarcomeres so they are not
striated. Skeletal muscle and cardiac muscle are specialized for rapid, forceful
contractions and so have their contractile proteins arranged in sarcomeres. Thus, cardiac
and skeletal muscle fibers are striated. Smooth muscle has involuntary innervation. Its
short, fusiform cells have one centrally placed nucleus per cell and no striations. Skeletal
muscle has voluntary innervation. Its long fusiform cells have many peripherally placed
nuclei per cell and striations. Cardiac muscle has involuntary innervation. Its short,
branched cells have one centrally placed nucleus per cell and striations.
Slide 12, Skeletal Muscle, H&E
This slide has two thin, plastic-embedded specimens of skeletal muscle, one cut parallel
to long axis of fibers, a longitudinal section, (LS) and the other cut perpendicular to the
long axis of fibers, a cross section (CS). Cytological detail is impressive. Start with the
cross section, observing fascicles separated by perimysium of CT, muscle fibers (cells)
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with peripheral nuclei, and endomysium with CT joining individual fibers. Learn how to
distinguish between the nuclei of fibroblasts and myocytes. Fibroblast nuclei are
thinner, wavy, darkly stained (more heterochromatin) and external to the muscle fibers.
Myocyte nuclei are fatter, smoother, lightly stained (less heterochromatin), have
nucleoli, and inside muscle fibers. Note that these skeletal muscle fibers are
multinucleated cells, are striated, and have peripheral nuclei. Be careful here. A grazing
section through a muscle fiber may show peripheral nuclei that appear to be central to the
cell. This is a plane of section phenomenon. You will certainly be able to find clear
examples where myocyte nuclei are peripheral to bundles of myofibrils. In the
longitudinal section, look for an area where striations are prominent. Identify myofibrils,
locate Z-lines, define the boundaries of a sarcomere, and then find A-bands and Ibands.
Slide 49, Esophagus, H&E
This is a cross section through the middle part of the esophagus. The esophagus connects
the oropharynx (all skeletal muscle) to the stomach (all smooth muscle). The upper
portion of the esophagus has all skeletal muscle, the middle portion is mixed skeletal and
smooth muscle, and the lower portion is all smooth muscle, in the muscularis externa. In
your section, the muscularis externa (ME) contains mostly skeletal muscle fibers but
also some bundles of smooth muscle. Between the mucosal epithelium at the lumen (L)
and the ME, you can find submucosal loose CT. This is an excellent slide to learn to
distinguish skeletal muscle (multinucleated, striated fibers with peripheral nuclei) and
smooth muscle (uninucleated, nonstriated fibers with central nuclei). It is also useful to
learn to distinguish between smooth muscle and surrounding irregular CT. Smooth
muscle has relatively more nuclei/unit volume. CT has relatively fewer nuclei per unit
volume. Test these criteria by counting number of nuclei in equal areas in both smooth
muscle and CT. Remember that you are looking at a section, so number of nuclei/unit
area is proportional to number of nuclei/unit volume.
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Slide 42, Posterior Tongue, H&E
This is a thin plastic section through the root of the tongue. Skeletal muscle fibers
(SkM) are abundant at the label. The minute purple structures scattered throughout the
section are compound tubuloalveolar minor salivary glands with mostly serous acini
and a few mucous acini. There are many interlaced bundles of skeletal muscle fibers.
Note their peripheral nuclei and striations.
Slide 9, Muscle-Tendon Junction, H&E
Skeletal muscles (M) are attached to bones by tendons (T). This slide is a thin plastic
section of a muscle-tendon junction. It is a good place the review dense regular CT
(tendon) and learn the distinction between fibroblast nuclei in the tendon and
perimysium and myocyte nuclei at the edges of muscle fibers.
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Slide 11, Heart, H&E
This is a thick section through the ventricle (V) of the heart. A papillary muscle (PM)
and a chorda tendinea (CT) are also visible. Look in the ventricle for cardiac muscle
fibers. Note that they are striated and have centrally placed nuclei. The fibers are
branched. Use the next slide to find intercalated discs.
Slide 10, Heart, H&E
This is a thin plastic section of the heart. At the bottom of the slide you can find the
endocardial surface. It faces on the heart lumen. It is lined by endothelium. What kind
of epithelium is the endocardial lining? Now use this slide to study the cytological details
of cardiac muscle fibers. Locate fibers cut longitudinally and notice their centrally placed
nuclei and branches. Sarcomeres with Z-lines, A-bands, and I-bands are visible.
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Slide MCO 93W3530. Intercalated Discs, Heart
This slide shows several large blood vessels (BV) (muscular arteries). These are branches
of the coronary arteries. They supply blood to the heart muscle. Between the blood
vessels, in the area labeled ID, (and in many locations elsewhere in this slide), you will
be able to find dark transverse bands that cross the entire myocyte. These are
intercalated discs, sites of intercellular junction between adjacent cardiac myocytes.
Numerous gap junctions are located in the intercalated discs. These are aqueous pores
between cells, allowing ionic flow and thus electrical currents that coordinate beating of
the heart.
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Slide 51, Duodenum, H&E
This is a cross section through the duodenum, the first part of the small intestine. You
should focus on the smooth muscle fibers in the muscularis externa, the pinker band
around the outer upper edge of the section. In the small intestine, there are two prominent
layers of smooth muscle. The inner layer is arranged circularly with respect to the lumen
and the outer layer runs parallel to the long axis of the tube, i.e., is longitudinal. In this
section, the inner circular fibers are cut more or less parallel to their long axes and have
bright red stripes across them in some areas. These contraction bands are fixation
artifacts. The outer longitudinal fibers are cut more or less perpendicular to their long
axis. Notice the relatively smaller size of smooth muscle fibers, the lack of striations, and
the centrally placed nuclei. The smooth muscle fibers are shaped somewhat like cigars
that are packed end-to-end. The nucleus is toward the center of the elongated cell.
Therefore, many sections do not include the nucleus while a few sections pass through
nuclei.
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Slide 50, Stomach, Corpic, Near Pylorus, H&E
The muscularis externa (ME) of the stomach also consists of several layers of smooth
muscle fibers. These are orthogonally arranged and follow the curvatures of the stomach.
Examine the smooth muscle fibers in the muscularis externa. You can also find a thin
band of smooth muscle fibers just deep to the mucosa (m). This is the deepest layer of
the mucosa. It is called the muscularis mucosae. Can you identify the gastric mucosal
epithelium?
Slide 67, Spermatic Cord, H&E
There are three overlapping layers of smooth muscle in the wall of the ductus deferens
(DD), a small tubular vessel that conveys spermatozoa from the epididymis to the
prostate gland. In ascending from the epididymis, the ductus deferens passes through the
spermatic cord, along with afferent and efferent blood vessels to the testis and
epididymis, and then passes through the inguinal canal. Examine smooth muscle fibers
in the inner and outer longitudinal layers and the middle circular layer. There is also a
good deal of smooth muscle in the walls of the numerous large blood vessels in this
specimen. This slide is a good place to compare and contrast smooth muscle and skeletal
muscle. There is a portion of the cremaster muscle (CM), an extension of the internal
oblique abdominal muscle. Although innervated by spinal nerves, the cremaster is an
unusual skeletal muscle in that one usually has no voluntary control over it. There is an
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involuntary cremasteric reflex, which lifts the testes toward the body cavity when an
individual is suddenly frightened or chilled.
Slide 73, Secretory Uterus, H&E
This is a thin plastic section through the entire thickness of the wall of the uterus. Starting
from the right, there is a thin outer CT capsule called the perimetrium (P), a thick
muscular middle layer called the myometrium (M), and an inner glandular endometrium
(E) at the lumen. This is a good place to study the relationship between smooth muscle
and surrounding CT. The nuclei of smooth muscle cells are cigar-shaped, with blunter
ends, and less heterochromatin. In contrast, the nuclei of fibroblasts are longer and
thinner, with a serpentine appearance, and more heterochromatin,
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Slide 64, Ureter, H&E
The mural portion of this tube, deep to the lumen (L) and its mucosa, has several layers
of smooth muscle in it. These contract peristaltically to move urine from the kidneys to
the urinary bladder. Identify smooth muscle fibers and surrounding CT fibroblasts. What
kind of epithelium is at the lumen? Where else in the body do you find this kind of
epithelium?
The picture below shows skeletal muscle fibers (smf), a small nerve (N) with branches
that run to motor end plates (MEP). Motor impulses travel from the spinal cord, down
the nerve to the motor end plate. Here, they trigger release of acetylcholine, which
triggers changes in the potential of the sarcolemma, eventually leading to muscle
contraction. How does the action potential get from the sarcolemma to the deep portions
of the muscle fiber? What organelle within the sarcoplasm stores Ca2+?
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The picture above shows a cross section of a muscle spindle surrounded by skeletal
muscle fibers (smf). This stretch receptor is composed of modified skeletal muscle,
bundles of intrafusal fibers (I). An inner capsule (IC) and an outer capsule (oc) of
connective tissue surround the muscle spindle. Although not shown in this
photomicrograph, muscle spindles have a sensory efferent innervation and a motor
afferent innervation. Sensory outputs are conveyed to the spinal cord and brain, where
they inform the individual about the state of activity of the muscle. Motor impulses to
these muscle spindles modify their contraction and modulate their sensitivity.
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LOWER RESPIRATORY SYSTEM
Objectives
•
•
•
•
•
Learn basic morphology of trachea
Learn to identify and distinguish different parts of conducting airway distal to
trachea including bronchi, bronchioles, terminal bronchioles, and respiratory
bronchioles
Understand structure and function of alveolar ducts, alveolar sacs and alveoli
Identify and understand function of type I cell, type II cells, and pulmonary
macrophages
Understand relationship between capillaries and alveoli
Overview
The lower respiratory system has two main components, the conducting airway
and the alveoli. The conducting airway conveys inspired air through the trachea, bronchi,
and bronchioles. The alveoli first appear in the walls of respiratory bronchioles and soon
completely line the walls of the alveolar ducts. Each alveolus is surround by a capillary
bed and lined by an alveolar epithelium. Respiratory gas exchange occurs in the thinwalled alveoli. Pulmonary macrophages are part of the mononuclear phagocyte system.
They have an important role in removing microorganisms and inspired debris that makes
its way into the distal reaches of the respiratory system.
Slide 37, Trachea, H&E
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The section on the left is a longitudinal slice of one half of the trachea. The luminal
surface is on the right. The section on the right is a cross section of one half of the
trachea. The luminal surface (L) is on the left (concave) side. At the bottom, part of the
band of trachealis muscle is visible. Mixed glands (G) are visible in the submucosa.
Hyaline cartilage (HC) dominates the wall of the trachea. First, examine the mucosa of
the trachea and find the pseudostratified, ciliated columnar (PCC) epithelium with
goblet cells. You should be able to identify three cell types in this epithelium: basal cells,
ciliated cells, and goblet cells. Two kinds of brush cells and small granule (APUD,
Kulchitsky) cells are also present by not easily seen. The basement membrane of the
tracheal epithelium is plainly visible as a light pink line between the epithelium and the
lamina propria. Deep to the epithelium, you will find a lamina propria with perhaps
small aggregates of lymphocytes and deep to that there is more connective tissue with
compound tubuloalveolar mixed glands. These drain to the tracheal surface by ducts.
These glands, along with goblet cells, secrete a layer of mucus and other moistening
fluids that protects the trachea and lungs. Inspired debris is trapped in the mucus and
swept upward, out of the respiratory system by proximal ciliary beating. C-shaped rings
of hyaline cartilage support the airway. This is a good juncture to review perichondrium,
fibroblasts, chondroblasts, chondrocytes, and ECM of hyaline cartilage. Outside the
hyaline cartilage, there is a layer of CT that bounds the trachea. Would you find a
mesothelium on the outer surface of the trachea?
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Slide LH0098, Trachea, H&E
This is a thin plastic section of a cross section of the trachea. Look at the luminal
epithelium near the letter L for lumen (L) on the inside of the tube. At high
magnification, locate this pseudostratified ciliated columnar epithelium with goblet cells.
First, locate the ciliated cells with the prominent apical cilia and apical nuclei. Next, you
will find numerous goblet cells. These have almost the entire apical portion of the cell
filled with bluish/purple mucous granules. There is also a thick, eosinophilic basement
membrane in the deepest portion of the epithelium. Just superficial to this basement
membrane, you will find many basal cells and perhaps even some Kulchitsky cells.
These are part of the APUD system and secrete cathecholamine- and peptide-rich
hormones that have localized effects, regulating goblet cell secretion, ciliary beating, and
other similar functions. The Kulchitsky cells are rare, but if you find a cell near the
basement membrane, with small purple granules and a reddish/purple cytoplasm, it is
probably one of these APUD cells. This is also a good place to review the characteristics
of smooth muscle in the posterior trachealis muscle (TM) and hyaline cartilage (HC).
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Slide 38, Lung, H&E
This is a section of a biopsy specimen taken from the free anatomical surface of the lung.
On the left, the curved surface, there is a thin CT capsule called the visceral pleura (VP).
Is it covered by a mesothelium? Why? There is a large bronchus (B) and its companion
branch of the pulmonary artery (PA). By looking around on this slide, you should be
able to find the following structures:
•
•
•
•
•
•
Bronchi = plates of hyaline cartilage and smooth muscle in wall
Bronchioles = only smooth muscle in wall
Respiratory bronchioles = a few alveoli in wall
Alveolar ducts
Alveolar sacs
Alveoli
The diagram on the next page shows part of this proximodistal transition from the
terminal bronchiole, through respiratory bronchioles, into alveolar ducts, terminating in
alveolar sacs consisting of many alveoli.
As one moves from proximal to distal in the airway of the respiratory system several
changes occur:
•
•
•
•
Diameter of individual airways decreases while total cross-sectional
area of entire airways increases (because of exponential increase in
number of airways due to branching)
Amount of cartilage decreases—C-shaped rings (trachea) < plates
(bronchi) < none (bronchioles)
Amount of smooth muscle increases—Only posterior (trachea) > mixed
with cartilage (bronchi) > entire wall (bronchioles)
Epithelium changes—PCC with goblet cells (trachea and bronchi, large
bronchioles), ciliated and Clara cells (terminal bronchioles), some alveoli
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in walls (respiratory bronchioles), all alveoli in walls (alveolar ducts and
sacs)
Atlas of Functional Histology, ed. 10. © 2005 LWW, Philadelphia, pg. 288
Now, at high magnification locate an alveolus. Study the cells lining the airway. Most are
extremely flattened. These are squamous alveolar epithelial cells (type I cells). They are
specialized for gas exchange. A few are located at septal junctions in particular, are
rounder, and have some washed-out cytoplasmic vacuoles. These are great alveolar
epithelial cells (type II cells, septal cells). They secrete surfactant. In the interalveolar
septa, you will see numerous round, bright red structures. These are pulmonary
capillaries stuffed with erythrocytes. Review the diagram below and then see if you can
sketch the relationship between the alveolar epithelium, basement membranes, capillary
endothelium, and trace diffusion of oxygen from the air space to the blood space.
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Macrophages should also be easy to locate in alveoli. There are large, irregular cells
marked by dark granules of ingested debris.
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CARDIOVASCULAR SYSTEM
Objectives
•
•
•
Review gross structure and layers (epicardium, myocardium, endocardium) of
the heart.
Study and learn to recognize major divisions of the vascular system:
Elastic artery (e.g., aorta)
Muscular arteries
Arterioles
Capillaries
Venules
Vein
Learn to relate structural and function differences in different classes of blood
vessels
Overview
The chief function of the cardiovascular system is to transport blood to and from
the respiratory system and the rest of the body. It consists of a four-chambered pump, the
heart, a system to distribute blood from the heart to capillary beds (arteries), and a system
to return blood from capillaries to the heart (veins). There are two main divisions of the
circulatory system, namely the pulmonary circulation and the systemic circulation.
The pulmonary circulation conveys deoxygenated blood from the heart to the lungs,
where it becomes oxygenated before returning to the heart. The systemic circulation
conveys oxygenated blood from the heart to the body and returns deoxygenated blood to
the heart, which pumps it through the pulmonary circuit for oxygenation. Capillaries are
specialized for transfer of oxygen and carbon dioxide, nutrients, and hormones across
their thin walls. Histologists describe three layers in the walls of structures in the
cardiovascular system:
•
•
•
An inner, tunica intima (called endocardium in heart), which consists of
an endothelium and a thin CT domain.
A middle, tunica media (called myocardium in heart), which consists of
contractile elements, either smooth muscle or cardiac muscle, and CT.
An outer, tunica adventitia (called epicardium in heart), which consists
of CT domains most often.
As you study different parts of the cardiovascular system, learn to relate structural
differences in different parts to the function of that part in the overall working of the
cardiovascular system.
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Slide 11, Heart, H&E
This specimen is taken from the top of the left ventricle. A papillary muscle (pm)
anchors a valve via a chorda tendinea (ct). Starting at the top of this section, examine
the endocardium (en), noting the simple squamous epithelium (endothelium) at the
lumen and a thin layer of CT, with some fibroblasts. Now move down into the
myocardium (my) and review the characteristic features of cardiac muscle fibers. In
the epicardium (ep), you will find a thicker CT domain, infiltrated with adipose tissue,
blood vessels that dip down into the myocardium to supply oxygenated blood to the
myocardium, and an outer mesothelium that is the most superficial part of the visceral
pericardium.
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Slide MCO 93W3530. Intercalated Discs, Heart
This slide shows several large blood vessels (BV) (muscular arteries). These are branches
of the coronary arteries. They supply blood to the heart muscle. Occlusion of these
vessels by atherosclerotic plaque will result in a heart attack (myocardial infarction).
Between the blood vessels, in the area labeled ID, (and in many locations elsewhere in
this slide), you will be able to find dark transverse bands that cross the entire myocyte.
These are intercalated discs, sites of intercellular junction between adjacent cardiac
myocytes.
Slide 10, Heart, H&E
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This specimen has the endocardial surface of the heart at the bottom. It is a thin plastic
section that shows the finer cytological details of cardiac muscle fibers to better
advantage and also has Purkinje fibers. These modified cardiac myocytes are part of the
cardiac conduction system. Purkinje fibers are similar to cardiac myocytes, except that
they have about twice the diameter of a cardiac myocyte. They have a large amount of
glycogen stored in the sarcoplasm. This unstained glycogen store increases the volume of
the cell and disperses the myofibrils so that they are less tightly packed. Thus, the
cytoplasm is less densely stained. Below is a good example of Purkinje fibers (pf), lying
just deep to the endocardium (en). Compare Purkinje fibers to the deeper myocytes
(mc).
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Slide MCO 93W3533, Heart, Purkinje Fibers
This specimen of the heart has some excellent examples of Purkinje fibers, located on
the endocardial surface of the heart in a small, oval, lightly stained area just below the PF
label in the thumbnail image above. The pericardial surface, with some adipose tissue and
a large blood vessel is in the top of the slide. Compare and contrast standard cardiac
myocytes with Purkinje fibers using this slide. Notice that the Purkinje fibers are more
lightly stained, have a larger diameter, have a few peripheral myofibrils, a centrally
placed nucleus, and a large perinuclear clear area that is packed full of glycogen granules
when compared with nearby cardiac myocytes.
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Slide 28, Aorta, H&E
It is easy to find the tunica intima (ti), tunica media (tm), and tunica adventitia (ta) in
this preparation. The thickest part of this vessel, the tunica media, consists of multiple
layers of fenestrated elastic laminae (dark pink, refractile bands) layered with lighter
pink areas consisting of smooth muscle fibers and many collagen fibers, secreting by the
smooth muscle cells. The elastic laminae in the media have large fenestrations. In reality,
they are concentrically arranged tubes of elastic fibers with large holes (fenestrations) in
the wall of the tubes. Thus, in cross section, the laminae appear discontinuous due to the
holes. When the left ventricle contracts, the wall of the aorta bulges out, storing some of
the energy of systole (ventricular contraction) by dilating the fenestrated elastic
laminae. When systole ceases, the fenestrated elastic laminae spring back to their original
shape. This elasticity helps propel blood along the aorta away from the heart. Observe
the endothelium of the tunica intima and the salient features of the tunica adventitia,
including nerve fibers, vasa vasorum, CT fibers, and adipocytes. Patients with Marfan
syndrome, a congenital defect in fibrillin structure, frequently die from sudden aortic
aneurysms at a young age. Why?
Slide 30, Aorta, Elastic Stain
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This slide is similar to the last one except it is stained for elastic fibers. Observe the
media with its multiple layers of wavy reddish brown elastic laminae, sandwiched
between CT collagen fibers (light blue) and smooth muscle (light yellow).
Slide 29, Aortic Valve and Aorta, H&E
This is section through the top of the left ventricle (lv). It also includes a part of the wall
of the aorta (a) and one of the three cusps of the aortic valve (av). There is fibrous CT in
the valve that merges into the CT (part of the cardiac skeleton) between the ventricle and
the aorta. Note that the valve is avascular and covered by an endothelium.
Slide 17, Artery, Vein, and Nerve, H&E
This is a cross section of an artery (A), vein (V) and nerve (N). Use this slide to study
the features of a typical large muscular artery and large vein. The most obvious
difference between the two vessels is the ratio of thickness of media to vessel diameter.
The muscular artery has approximately a 1/5: wall thickness/diameter ratio. In contrast,
the companion vein has approximately a 1/15: wall thickness/diameter ratio. Note also
that the outline of the artery is relatively smooth whereas the outline of the vein is
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irregular. Veins often have more blood in their lumen. Now study the walls of both large
vessels and identify the three tunics. While you on this slide, see if you can find
arterioles, venules, and capillaries.
Slide 47, Epiglottis, Elastic Stain
This is an excellent slide for studying small muscular arteries and arterioles, located in
the connective tissue surrounding the elastic cartilage (EC) in the middle of the
epiglottis. The elastic stain stains the elastic fibers in this specimen a dark purple/black
color. A counter stain conveniently stains RBCs yellow so look for these inside blood
vessels. You can find numerous small muscular arteries (with a prominent wrinkled
internal elastic lamina, 5-10 layers of smooth muscle in the media, and a sparse
external elastic lamina. Arterioles have about 2 layers of smooth muscle in the media
and little or no internal elastic lamina. The distinction between the smallest muscular
arteries and the largest arterioles is slight and of no great significance. The arteries may
be accompanied by veins and the arterioles may be accompanied by venules. Capillaries
are also present.
Slide 34, Efferent Ductules, H&E
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This thin plastic section from the male reproductive system has a lot of CT (pink)
between efferent ductules (purple lumina). Fixation and staining here is excellent. You
will be able to find small muscular arteries, companion veins, arterioles, venules, and
many capillaries. Find several examples of each and learn criteria used to discriminate
between these different types of small vessels.
Slide 60, Liver, H&E
This is a thin plastic section of the liver. It consists of cords and plates of hepatic
parenchymal cells surrounded by hepatic sinusoids. In any given organ, the
parenchymal cells are the organ-specific cells. Be aware that many organs have both
parenchymal and nonparenchymal cells, e.g., CT, blood vessels, nerves, lymphatics. A
sinusoid is a generic term for a capillary. It implies that there is sluggish, meandering
blood flow through a network of capillaries with large lumina. Sinusoids are also found
in bone marrow, the spleen, endocrine organs, etc. Sinusoids are just capillaries. The
hepatic sinusoids carry nutrient-laden blood from the GI tract and as they pass by the
hepatic parenchymal cells, the nutrients leave the blood and enter the liver, for
processing. Hepatic sinusoids are unusual capillaries. They are intermingled stretches of
discontinuous capillaries and fenestrated continuous capillaries, although these details are
not visible in this slide. Furthermore, there are two distinct types of marginal cells. One is
a flattened, typical endothelial cells and the other is a fatter, phagocytic Kupffer cell.
The capillaries here have one additional peculiarity—they have a thin, discontinuous
basement membrane. In this preparation, one can see numerous flattened endothelial cell
nuclei but the Kupffer cell nuclei are harder to locate and difficult to differentiate from
hepatic parenchymal cells.
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Slide 90, Pituitary Gland, H&E
The pituitary gland is the master endocrine organ of the body. It has two main
components, a neurohypophysis (N) (really an extension of the central nervous system,
directly connected to the brain’s hypothalamus) and an adenohypophysis (A). Look in
the adenohypophysis. At high magnification, you can see a plethora of capillaries
(properly called sinusoids) engorged with RBCs. The adenohypophysis is an endocrine
organ, i.e., it secretes its hormones, synthesized in plates, cords, and follicles of epithelial
cells, into the blood in the capillaries that surround the epithelial cells. Like all other
endocrine glands, these capillaries are continuous fenestrated capillaries. At high
magnification, you can see the flattened nuclei of capillary endothelial cells. The
fenestrations are not visible in the light microscope.
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Slide UW175, Abdominal Vein, H&E
This is a transverse section through a large vein in the abdomen. Start at the lumen (L)
and work your way outward into the wall of the vessel. First, you will note a thin tunica
intima with its endothelial cells. Next, you will enter a pinkish tunica media (TM)
which consists mainly of smaller, tightly packed smooth muscle cells arranged more or
less circumferentially with respect to the lumen. Finally, look at the tunica adventitia
(TA) and note the lighter, larger bundles of smooth muscle, surrounded with pink borders
of collagen fibers. These bundles are arranged more longitudinally than the more
circumferential fibers in the tunica media.
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LOWER DIGESTIVE TRACT I
ESOPHAGUS AND STOMACH
Objectives
•
•
•
Learn the regional differences in the gut tube and relate these differences to
digestive function.
Learn the basic architecture of digestive viscera. All tubular components of the
digestive system have four basic layers to the wall. Starting at the lumen (where
food is contained) and moving toward the outer wall of the organ, these layers
are:
(1) Mucosa (mucosal epithelium, lamina propria, and muscularis
mucosae)
(2) Submucosa
(3) Muscularis externa
(4) Adventitia
Identify the different epithelial cell types in the mucosal epithelium and relate
these specific cell types to digestive function
Overview
First, we need to learn the basic structural organization of the tubular components
of the digestive system. We can examine this basic organization in the esophageal cross
section below:
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Starting from the lumen and moving outward through the wall, one first
encounters the mucosa (m). This consists of an epithelial lining (the mucosal
epithelium), a loose CT domain called the lamina propria, and a thin layer of smooth
muscle called the muscularis mucosae (mm). Deep to the muscularis mucosae, one
encounters a broad CT domain called the submucosa (sm). Next, there is a thick layer of
smooth muscle fibers called the muscularis externa, typically consisting of an inner
circular (IC) and an outer longitudinal (OL) layer of smooth muscle fibers. All of this is
encapsulated in a thin CT layer called the adventitia (a). If the adventitial CT is covered
by a mesothelium, e.g., in intraperitoneal portions of the GI tract, we call this outer layer
the serosa rather than adventitia. Let me illustrate this distinction by example. The
superior esophagus passes through the mediastinum and has no peritoneal covering.
Therefore, this outer capsule of the esophagus is called an adventitia. However, the
inferior end of the esophagus, after it pierces the diaphragm but before it enters the
cardiac stomach, is intraperitoneal, is covered by a mesothelium, and therefore is covered
on the outside by a serosa. Similarly, the posterior surface of the ascending colon is
(secondarily) retroperitoneal and therefore has an adventitia. In contrast, the anterior
surface of the ascending colon is intraperiotoneal and therefore has a serosal covering.
This basic organization should become as familiar to you as you social security
number or your telephone number. Use these four layers to organize your study of the GI
system. Make a big chart by region and fill in diagnostic features of each layer. Link the
regional structural variations to regional functional variations. Then practice identifying
GI unknowns by characterizing each of the four basic layers from a structural and
functional perspective. If you want to get really good at this, get a partner to present you
with GI unknowns, from the computer or from pictures in a book, and then analyze the
specimen by examining all four layers. Once you have come to a tentative identification
of the unknown, test your identification. For example, if you think you have middle
esophagus, test this hypothesis by realizing that middle esophagus should have mucous
glands in the submucosa and mixed skeletal and smooth muscle in the muscularis
externa. It is time to look at some actual specimens and begin learning about the
microscopic anatomy of the GI tract.
In general, the upper digestive system is dedicated to preparation of food for
digestion (in oral cavity), conveyance of food to stomach (esophagus), and initial phases
of digestion in an acidic environment (stomach). Digestion is completed in the small
intestine and most absorption of nutrients also occurs here. The large intestines are
principally dedicated to processing of indigestible components of food for formation and
expulsion of feces.
The overview diagram below illustrates the salient features of the esophagus and
stomach. Study it carefully before looking at slides.
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Atlas of Functional Histology, ed. 10. © 2005 LWW, Philadelphia, pg. 228
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Slide 49, Esophagus, H&E
This is a cross section through the middle one-third of the esophagus. Use this slide to
review the four basic layers of a GI organ. Start at the lumen (L) and work through the
wall to the muscularis externa (ME) and finally the adventitia. The mucosa has
transient folds that are flattened out as a bolus of food passes and a stratified squamous
unkeratinized epithelium. What is its function? There are only a few lymphocytes in
the lamina propria and the muscularis mucosae is a prominent band of smooth muscle.
The submucosa has some small mucous glands with ducts. The muscularis externa is
mostly skeletal muscle but there is a bit of smooth muscle there as well. Ganglia and
nerve fibers of the myenteric (Auerbach) plexus are easily seen between the two layers
of the muscularis externa. The adventitia has no mesothelium.
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Slide 79, Gastroesophageal Junction, H&E
This is a section through the gastroesophageal junction. The esophageal mucosa (EM)
and the gastric mucosa (GM) are both marked. There is a thickening of the inner circular
layer of the muscularis externa that serves as a sphincter (S). The esophageal mucosa has
a stratified squamous unkeratinized epithelium that changes suddenly to a simple
columnar epithelium at the gastroesophageal junction. The gastric mucosa of the cardiac
portion of the stomach has transient submucosal folds (rugae) that flatten when the
stomach fills and many shallow pits (foveolae) lined by a simple columnar epithelium
with mostly mucous cells. These glands are characteristic of the cardiac stomach. The
blue blob just downstream from the GM label in the cardiac stomach is a lymphoid
nodule, where there are many lymphocytes aggregated into a nodule that infiltrates both
the mucosa and submucosa. Since we are now in the lower esophagus, there is no skeletal
muscle, only smooth muscle in the muscularis externa of both the esophagus and the
stomach. The adventitia has a mesothelial covering and is therefore properly called a
serosa.
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Slide SL012, Fundic Stomach, H&E
This is a wonderfully detailed section through fundic stomach. The fundic and corpic
stomach are very similar histologically. While these two regions of the stomach are
different on the gross level, histologically they are indistinguishable. Start at the gastric
mucosa (GM) and find the boundaries of the four layers. On the left, there is a small ruga
that includes lamina propria, muscularis mucosae, and the submucosa. Now increase the
magnification and study the gastric pits. These are deep surface invaginations. Go to high
magnification and find a gastric gland that is sectioned parallel to its long axis. Starting at
the superficial part of a pit, identify the following cells: mucous surface cells (superficial
cells with numerous apical mucus globs- mucus is lightly stained), mucous neck cells
(similar to mucous surface cells but located in neck of gland-histochemical studies reveal
that these cells have a slightly different mucus from mucous surface cells- they look very
much like mucous surface cells in H&E but are found in the superficial necks of the
glands), parietal cells (large, round, acidophilic cells that are most numerous in middle
portions of glands), chief cells (small, pyramidal, basophilic cells that are most numerous
in deep portions of glands). The mucous cells secrete protective mucus. The parietal cells
secrete HCl and make gastric intrinsic factor. The chief cells secrete pepsinogen. There
are also enteroendocrine (APUD) cells present here but they don’t show up well on H&E
preparations. The enteroendocrine cells secrete peptides and catecholamines (e.g.,
gastrin-secreting G cells, regulate HCl secretion or serotonin-secreting EC cells). The
diagram below shows these cell types to good advantage:
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Why are parietal cells acidophilic? Why are chief cells basophilic?
Slide 50, Stomach, Corpic, Near Pylorus, H&E
The mucosa (m) of this slide still has gastric glands typical of fundic/corpic stomach,
although they are not as deep as those in the last slide. The four major cells of gastric
glands are still present, however. The large, submucosal folds are rugae. Can you define
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a ruga? What happens to them as the stomach fills and becomes distended? The
muscularis externa (ME) has two layers of smooth muscle more or less orthogonally
arranged. In the stomach, the layers of smooth muscle follow the great curves of the
organ. Therefore, since the stomach is not a simple tube, but rather a dilated, curved sac,
the two layers of smooth muscle are not neatly arranged as an inner circular layer and an
outer longitudinal layer.
Slide SL050, Pyloric Stomach, H&E
This slide is a section of the pyloric stomach. The gastric mucosa (GM) is on the left. The
muscularis externa (ME) is on the right. The submucosa is between the two. Study the
gastric mucosa carefully. There are numerous gastric glands here. They are relatively
straight for most of their length, although the deep portions near the muscularis mucosae
are somewhat coiled and branched. The glands connect with gastric pits and empty their
viscous mucous secretions into the pits. The epithelial cells lining the glands and pits
resemble mucous surface cells of the fundic/corpic stomach but parietal and chief cells
are largely absent. The lamina propria of the pyloric stomach has numerous resident
fibroblasts as well as an abundance of immigrant leucocytes, including lymphocytes,
plasma cells, neutrophils, and eosinophils.
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Slide 77, Gastrointestinal Junction, Pyloric Stomach
and Duodenum, Masson Trichrome
This slide includes both a segment of the pyloric stomach (PS) and the duodenum (D).
Note also that the muscularis externa (ME) is dramatically thickened to form the
pyloric sphincter. The pyloric stomach has rugae (transient submucosal folds) with lots of
submucosal CT in them. In this stain, collagen fibers are green. Examine the glands of
the pyloric stomach at higher magnification. These glands are much shallower than those
found in fundic/corpic stomach and are almost exclusively mucous cells. Now switch
over to the duodenal mucosa. Here one finds low, permanent, submucosal folds (plicae
circulares) covered by villi. This is the beginning of the duodenum. The villi are covered
by an epithelium that is simple columnar with mostly tall columnar absorptive cells and a
few goblet cells. Deep to the muscularis mucosae, one encounters submucosal Brunner
glands. These are restricted to the duodenum. They secrete mucus and bicarbonate. What
is the function of Brunner glands? When cut in cross section, an area rich in villi can look
quite like an area rich in pits. How can you tell them apart—the villi will consist of cores
of CT surrounded by epithelium—the pits will consist of fields of CT filled with circles
of epithelium (see labeled photographs, pages 106 and 107 below).
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LOWER DIGESTIVE TRACT II
SMALL AND LARGE INTESTINES
Objectives
•
•
•
•
•
Learn the characteristic features of duodenum, jejunum, ileum, vermiform
appendix, colon, and anus and be able to distinguish these regions of the lower
digestive tract.
Understand the difference between plicae circulares, villi, microvilli, crypts, and
glands.
Identify and understand function of major epithelial cell types and resident vs.
immigrant cells in the lamina propria
Find good examples of the myenteric (Auerbach) and submucosal (Meissner)
plexus.
Locate enteroendocrine cells and understand there role in gastrointestinal
physiology
Overview
The small intestines are about 11 m long. The first (and shortest) part is the
duodenum. The duodenum receives acidic chyme from the stomach, neutralizes it, and
mixes chyme with bile (from the liver) and digestive enzymes (from the pancreas). The
duodenum has small plicae circulares, short villi, and submucosal Brunner glands. The
second (and longest) part is the jejunum. Most of the digestion and absorption of
nutrients occurs here. It has large plicae ciculares and long villi. The third part is the
ileum. The plicae circulares are again smaller, the villi are shorter, and there is an
abundance of lymphoid tissue in the lamina propria and submucosa (Peyer patches). Now
digested food passes into the large intestine. Water and residual nutrients are absorbed
here and waste is mixed with mucus to form feces. The feces are then expelled
periodically through the anus.
The small intestines are dedicated to digestion and absorption. They have great
length (and therefore great surface area), submucosal folds (plicae circulares-more
surface area), villi (more surface area), villi covered by an epithelium with apical
microvilli (more surface area), and a fuzzy coat of glycocalyx on microvilli (still more
surface area). Villi (finger-like projections), extending from the free anatomical surface
of the organ into the lumen, are uniquely found in the small intestines. In addition, there
are deep invaginations from the free anatomical surface called crypts (intestinal glands).
In the duodenum only, these crypts penetrate the muscularis mucosae (into the
submucosa) to form Brunner glands. In the jejunum and ileum, the crypts end at the
muscularis mucosae.
107
The large intestines are dedicated to formation of feces. All gross anatomical
segments are histologically similar. They have deep cryptic invaginations of the free
anatomical surface but no villi. There is a preponderance of goblet cells in the mucosal
epithelium. The muscularis externa has a uniformly thick inner circular layer and an outer
longitudinal layer with variable thickness. In most locations, the outer longitudinal layer
is thin, but contains three thick bands (teniae coli), which are equally spaced around the
periphery of the colon. Their contractions form sacculations of the wall called haustra.
The overview diagram below summarizes the salient features of the small intestine and
large intestine. Study it carefully before looking at your slides for today.
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Atlas of Functional Histology, ed. 10. © 2005 LWW, Philadelphia, pg. 252
This is a good spot to clarify the histological distinction between villi in the small
intestine and crypts or glands in the small intestine and large intestine. The villi are
restricted to the small intestine and are covered by an epithelium that is simple columnar
with mostly tall columnar absorptive cells and a few goblet cells. Deep to the muscularis
109
mucosae, one encounters submucosal Brunner glands. These are restricted to the
duodenum. They secrete mucus and bicarbonate. What is the function of Brunner glands?
When cut in cross section, an area rich in villi can look quite like an area rich in crypts or
intestinal glands. How can you tell them apart? The villi will consist of cores of CT
surrounded by epithelium. In contrast, the crypts or intestinal glands are present in both
the small and large intestine and consist of fields of CT filled with circles of epithelium:
Villi in Cross Section
110
Crypts or Intestinal Glands in Cross Section
Now you are ready to look at some slides of small and large intestines.
111
Slide 51, Duodenum, H&E
This is a cross section of about half of the duodenum with a small piece of the pancreas
(P) included. Start at the lumen (L) and identify the four basic layers. Now at higher
magnification, observe villi, with many absorptive cells and a few goblet cells, the
discontinuous muscularis mucosae and submucosal Brunner glands. The muscularis
externa has a clear inner circular and an outer longitudinal layer. Darker pink stripes in
inner circular layer are contraction bands, a fixation artifact. You will be able to see the
myenteric plexus clearly between the two layers of the muscularis externa. Scan along
the deep part of the crypts. Here and there you will find Paneth cells with large, bright
pink granules. These lie at the deepest part of the crypts, at the mucosal-submucosal
boundary. Thin slips of smooth muscle here are the muscularis mucosae. Deep to the
muscularis mucosae, the crypts lead into Brunner glands with mucous cells in them.
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Slide 52, Jejunum, H&E
The jejunum has very large plicae circulares (PC). Observe the villi facing the lumen
(L). They are long and their distal tips can be flattened. They are covered by absorptive
and goblet cells. There are no Brunner glands and the muscularis externa (ME) has two
neat layers with a myenteric plexus between. Paneth cells are numerous at the bases of
the crypts.
Slide 53, Ileum, H&E
Start at the lumen and identify the four layers. The most obvious feature of this slide is
the superabundance of lymphoid nodules (ln) (Peyer patches) in the submucosa. There
is also massive lymphoid infiltration into the lamina propria. You may be able to
identify plasma cells and lymphocytes in the lamina propria but don’t spend a lot of time
on this, because this is a thick section with relatively poor fixation. Note also that there
are many more goblets cells in the mucosal epithelium (m). The layering on the
muscularis externa (me) is particularly clear here and you can find the myenteric
plexus.
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Slide 61, Jejunum, Fontana Stain
This section of the jejunum has been stained with silver salts and counterstained with a
pink dye. You can tell that you are looking at the jejunum because there are huge
submucosal folds (plicae circulares) and long, distally expanded villi. The silver salts are
reduced to silver metal (black) by the chromaffin granules in enteroendocrine cells and
the reducing power of collagen fibers that encapsulate autonomic ganglia. We have two
jobs on this slide: (1) find enteroendocrine cells in mucosal epithelium and (2) study
parasympathetic myenteric (Auerbach) and submucosal (Meissner) plexus. Start at low
power at the top of the slide. Find villi cut parallel to their long axis. They will have a
core of CT covered by a mucosal epithelium. Scattered throughout the mucosal
epithelium, you can find many cells with small black granules in them. These are
enteroendocrine cells. Their secretions reduce silver salts and cause deposition of
staining silver metal. There are several different types of enteroendocrine cells present
here but they all look more or less alike. Specific immunohistochemical techniques
would be required to identify subtypes of enteroendocrine cells. Now find the muscularis
mucosae and look along its deep (submucosal) side. You may find scattered, sparse,
poorly-fixed neuron cell bodies (or small clusters of them). These are not easy to find but
they are there. These neurons have large round nuclei and prominent nucleoli. These are
neurons of the submucosal (Meissner) plexus. Next, move out to the boundary between
the inner muscularis externa (ime) and outer muscularis externa (ome). Along this
boundary there are prominent collections of neurons encapsulated by a thin CT capsule of
black fibers. You may also be able to find nerve fibers connecting these ganglia. This is
the myenteric (Auerbach) plexus. Although not obvious in this slide, the ganglia of
the myenteric plexus and the submucosal plexus are connected by thin nerve fibers.
Name two functions for this parasympathetic innervation. Do you know anything about
the embryonic origin of these neurons?
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Slide 54, Vermiform Appendix, H&E
This slide is a cross section through the vermiform appendix, a cul de sac of the cecum
adjacent to the ileocecal valve. It has features characteristic of the colon, namely a simple
columnar epithelium with mostly goblet cells, crypts rather than villi, a thick inner
circular and a thin outer longitudinal muscularis externa, extensive lymphoid infiltration
of the lamina propria, and numerous lymph nodules in the submucosal. It differs from
the ileum because it has crypts rather than villi. Does this organ have an adventitia or a
serosa? Why? If an inflamed appendix were to rupture, the bacteria in its lumen (L)
would be spilled into which body cavity?
Slide 55, Colon, H&E
This is a portion of the wall of the colon. It has a folded mucosa (m) caused by
contraction of the small muscle in the inner muscularis externa (ime). Notice that this
layer is considerably thicker than the much thinner outer muscularis externa (ome). The
teniae coli are three longitudinal thickenings of this otherwise thin layer but are not in
this specimen. There is extensive lymphoid infiltration of the lamina propria and a small
lymphoid nodule (l) that extends well into the submucosa. The mucosal epithelium
115
consists of numerous deep glands (not villi) lined mostly by goblet cells. These surface
invaginations end abruptly at the muscularis mucosae.
Slide 56, Rectoanal Junction, H&E
This slide passes through the junction between the rectum, which has a well-defined
muscularis mucosae and a simple columnar epithelium with goblet cells (sc) ; and, the
anal canal, which has a less well-defined or even lacks a muscularis mucosae and has a
stratified squamous unkeratinized epithelium (ss). The large pink structures at the top
right are dilated hemorrhoidal vessels filled with blood. The internal anal sphincter is
a thickening of the circular inner smooth muscle of the muscularis externa of the rectum.
The external anal phincter consists of skeletal muscle. Neither structure is included in
your specimen.
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LIVER, GALLBLADDER, AND PANCREAS
Objectives
•
•
•
•
•
•
Study and understand basic microscopic anatomy of the liver. Trace blood flow
from portal triad through sinusoids to central vein. Trace bile flow from canaliculi
to bile ducts.
Be able to find portal triads, identify their components, and understand the
vascular role of the portal veins and hepatic arteries, and bile ducts.
Learn characteristic features of gallbladder
Learn to distinguish between the exocrine and endocrine portions of pancreas.
Study and be able to identify the different ducts found in exocrine pancreas.
Find islets of Langerhans, with A cells and B cells, and understand relationship
between endocrine cells and capillaries.
Overview
The liver is one of the largest organs in the body and is vital for many functions
including synthesis of blood proteins, synthesis of apolipoproteins, detoxification of
drugs and metabolic wastes, and, of course, processing the products of digestion. It has a
dual blood supply, one from the systemic circulation and a second from the hepatic portal
system. The portal component is functionally crucial. In general, a portal system consists
of two capillary beds connected by large drainage vessels. Basically, nutrient-laden
(portal) vessels drain from the stomach and small intestines, carrying the products of
digestion directly to the liver, where they are processed and stored. After hepatic
processing, central veins drain blood into the hepatic veins, inferior vena cava, and thence
to the systemic circulation. The best way to learn about liver function is to master hepatic
blood flow.
In lecture and in lab, you will be exposed to the lobular organization of the liver.
Histologists have defined several sorts of structural subunits of the liver. The easiest to
find is the classical lobule. This is a hexagonal structure with portal triads at all six of
angles of the hexagon. In the middle of the classical lobule is the central vein. There is
another way to describe lobulation in the liver, namely using the portal lobule. This is a
triangular structure with three central veins at the points of the triangle and a portal triad
in the middle. Some histologists also speak of a liver acinus. This is an ellipsoidal
structure with portal triads at opposite ends of the ellipsoid along the major axis. While
examining the liver specimens below, keep these different ways of describing the
microscopic anatomy of the liver in mind. In the specific directions for the slides, we will
tell you precisely what you can and can’t see in the slides.
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The gallbladder is a cystic dilation at the end of the cystic duct. It receives bile
from the liver, stores and concentrates it, and empties bile into the duodenum when
needed for digestion. Bile is a complex mixture of heme breakdown products (e.g.,
bilirubin) and bile salts (e.g., deoxycholate). The bile salts are potent detergents that help
emulsify dietary fats and aid their digestion.
The pancreas is both an exocrine and an endocrine gland. In the acini, pancreatic
acinar cells synthesize and secrete a complex family of digestive enzymes. These are
released from the pancreas via a complex system of ducts, into the duodenum, where they
contribute mightily to digestion of foods. In addition, the endocrine portion of the
pancreas, the islets of Langerhans, secretes insulin, glucagon, and other peptides with
complex regulatory roles in carbohydrate and lipid metabolism. The islet tissue is
intimately associated with a glomerulus of fenestrated capillaries that carry the hormonal
secretions into the systemic circulation.
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Slide 60A, Liver, Mallory Stain
This specimen is from a nonhuman mammal, probably a pig. It has been stained with
Mallory stain. Pigs have much more interlobular CT than humans. In Mallory stain, CT is
blue. At low power, you can see many classic lobules (cl1 and cl2) neatly demarcated by
blue CT. These classic lobules are more or less hexagonal. Look for central veins toward
the middle of the classical lobule. They are the faint holes near the centers of the
burgundy classical lobules. In the blue CT septa, at the angles of the polygonal lobules,
you will easily find portal triads. Now use this slide to define a portal lobule. You can
use the three central veins of the three classic lobules between and to the right of cl1 and
cl2.
Slide 60, Liver, H&E
This is a lovely thin plastic section of human liver. Scan the slide at low magnification.
You will see plates and cords of granulated cells with round nuclei, peripheral
heterochromatin, and prominent nucleoli. These are hepatic parenchymal cells. Between
the plates of parenchymal cells you will find vascular sinusoids lined by endothelial
cells. There are few RBCs in sinusoids, but they are marked by neutrophils. You will also
find large vascular spaces filled with RBCs, in the center of masses of hepatic
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parenchymal cells. These are central veins. They are located in the center of a classical
lobule and receive blood from the sinusoids and drain into the hepatic vein. Now find CT
on the edge of the classical lobule. Here you can find the three components of the portal
triad: 1) hepatic arterioles (a smaller diameter vessel— an endothelium, and a few
layers of smooth muscle; 2) branches of the portal vein (a venule with larger diameter—
an endothelium, and only scant evidence of mural smooth muscle; and 3) a hepatic (bile)
duct, lined by a simple cuboidal epithelium. Where do the branches of the portal vein
send blood? Where do the hepatic arterioles send blood? Learning blood and bile flow in
the liver is the way to go here. If you understand that, you will understand how the liver
works in health and disease.
Now find some hepatic parenchymal cells at high magnification. Among clusters of
parenchymal cells, you can see pink, refractile, branching spaces. These are bile
canaliculi, formed by tight junctions (not visible in light microscope) between
parenchymal cells. Yes, the liver is a big exocrine gland. What is its exocrine secretion?
Now look on the opposite side of the parenchymal cells. Here, they face the lumen of
sinusoids. There is a space of Disse between the basal surface of the parenchymal cells
and the vascular endothelial cells. With a little imagination, you can see it but don’t be
alarmed if you can’t find it. The lumina of the sinusoids have very few RBCs but are
marked by scattered neutrophils. The endothelial cell nuclei are highly flattened and
darkly stained. You may also be able to find Kupffer cells with their large round nuclei
appearing to protrude into the sinusoidal lumen. Now see if you can define an example of
a portal lobule and an acinus.
Slide 25, Lymph Node/Liver, Silver Reticulum Stain
This slide has a section of lymph node (LN) and liver (L) together on one slide. Study
only the liver right now. The sections have been stained with a silver stain for reticular
fibers and a pink counterstain for nuclei. At high magnification you will see many black
reticular fibers. These are especially abundant in the connective tissues that bind
classical lobules. At the edges of classical lobules, you will be able to find the portal
triads. Each central vein is also set off by a thin band of reticular fibers. If you look
carefully at the most delicate parts of the black fibrous meshwork, you will see that
reticular fibers outline and support sinusoids.
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Slide 66, Gallbladder, H&E
If you start at the lumen (L) and move slowly through the wall of the gallbladder, you
will probably think at first that this looks very similar to small intestine. The mucosa is
folded into structures that look superficially like villi but you should observe that the
mucosal epithelium is simple columnar without goblet cells. More careful examination
reveals that these mucosal folds are more branched than simple villi and have tortuous
Rokitansky-Aschoff sinuses that appear as a white space, surrounded by epithelium,
surrounded by lamina propria. These are cross sections through bends in the sinuses.
When the sinues are deep and perhaps cut off from the lumen, they can retain bacteria or
sludgy bile and become inflamed. They are antecedents to pathological changes in the
gallbladder. There is no muscularis mucosae so there is no clear boundary between the
mucosa and the submucosa. Furthermore, the mural smooth muscle is much thinner than
you would find in the small intestine. So, when you see “villi” covered by a simple
columnar epithelium without goblet cells and a thin muscularis externa, think gallbladder.
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Slide 57, Pancreas, H&E
This slide is a good place to study basic histology of the pancreas. Note that there are
three lobules present in this slide, one upper right, one upper left, and a third across the
bottom of the specimen. Bright pink CT and blood vessels delineate borders of lobules.
Scan a lobule to find exocrine tissue and endocrine tissue. Now see if you can find
portions of the exocrine ducts. Start at an acinus. Acinar cells have many bright pink
apical zymogen granules. Acinar cells secrete their digestive enzymes into a complex
duct system that begins at centroacinar cells, continues down to intralobular and then
interlobular ducts in CT septa, and eventually empties into the main pancreatic duct.
Islet tissue is also evident in many locations. Use the next slide to study cytological
details of the pancreas.
Slide 58, Pancreas, H&E
This slide is a thin plastic section with impressive cytological detail. Locate an acinus
and notice the apical zymogen granules, basophilic cytoplasm in the basal portion of
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acinar cells, and the large, round nuclei with prominent nucleoli. Centroacinar cells and
other distal portions of the ducts are visible as pale-staining cells adjacent to the acini.
Centroacinar cells are the distal ends of the intercalated ducts, which empty into larger,
proximal intralobular ducts, which then drain into larger interlobular ducts found in
broad CT trabeculae. They are tightly joined to one another and plug into the lumen of
acini, sealing this lumen from the surrounding extracellular spaces. This prevents
digestive enzymes from escaping into the surrounding tissues, entering the blood, and
auto-digesting an individual. In patients with inflammation of the pancreas (pancreatitis),
one can find huge elevations of pancreatic enzymes such as pancreatic amylase in blood.
This is not good!
Now study some islet tissue. You can see capillaries surrounding the endocrine tissue.
With a little imagination, you may be able to define two populations of endocrine cells:
• A (alpha) cells are about 20%-30% of the total islet tissue-on periphery of islet,
have large nuclei-secrete glucagon
• B (beta) cells are about 70%-80% of total islet tissue- central- have small
nucleus-secrete insulin
Do not spend a lot of time at this, because the distinctions are subtle. There are also
several other minor kinds of cells here but they do not show up without special stains.
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IMMUNE SYSTEM
Objectives
•
•
•
Identify diffuse lymphoid tissue and lymphoid nodules.
Compare and contrast morphological features of tonsils, lymph nodes, spleen, and
thymus.
Be able to relate location and structure of major immune organs to the overall
function in the immune system.
Overview
Diffuse lymphoid tissue can be found nearly anywhere in the body. It is a
particularly prevalent feature of the GI tract and the respiratory system. Both systems are
open to the outside world and are constantly being bombarded by pathogenic
microorganisms. Diffuse lymphoid tissue consists of isolated lymphocytes or small
aggregates of lymphocytes and plasma cells residing in loose CT. Lymphoid nodules are
packed collections of lymphocytes that may or may not have germinal centers. Both
diffuse lymphoid tissue and lymph nodules are unencapsulated. Aggregates of lymphoid
nodules occur at important transition zone, e.g., the pharyngeal-esophageal transition,
gastroesophageal junction, ileocecal junction, and rectoanal junction.
Tonsils guard the pharyngoesophageal junction. We will study the palatine tonsil,
located in the oropharynx and associated with stratified squamous unkeratinized
epithelium. The vermiform appendix guards the ileocecal junction and is associated with
colonic epithelium. Lymph nodes are responsible for immune surveillance of lymph. The
spleen is responsible for immune surveillance of the blood. The thymus is a specialized
organ for T-cell maturation and dispersal.
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Slide 79, Gastroesophageal Junction, H&E
This slide contains the gastroesophageal junction. The esophageal mucosa (em) and
gastric mucosa (gm) are marked for orientation. There is a medium-sized lymphoid
nodule (l) in the gastric mucosa/submucosa. Start at medium magnification at the
epithelial transition zone and slowly work you way down to the lymphoid nodule. In the
lamina propria above the nodule, you can see scattered lymphocytes (small, dark
nucleus, thin shell of cytoplasm) and plasma cells (larger, oval cell with eccentric
nucleus and faintly purplish cytoplasm- basophilia). Notice that the lymphoid nodule
extends well into the submucosa (deep to the muscularis mucosae) and has a lighter
germinal center.
Slide 51, Duodenum, H&E
This slide is included to show you the relative paucity of lymphoid tissue in the
duodenum, as compared to the next slide. You will want to look at the cells in the lamina
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propria. Here and there you will see eosinophils with bi-lobed nuclei and bright red
granules. There are few lymphocytes and plasma cells evident in this specimen.
Slide 53, Ileum, H&E
The most obvious feature of this slide is the superabundance of lymphoid nodules (ln)
(Peyer patches) in the submucosa. There is also massive lymphoid infiltration into the
lamina propria. You may be able to identify plasma cells and lymphocytes in the
lamina propria but don’t spend a lot of time on this, because this is a thick section with
relatively poor fixation.
Slide 54, Vermiform Appendix, H&E
Here, and in the ileum, there is extensive lymphoid infiltration of the lamina propria and
submucosa, with numerous active lymphoid nodules (ln) with prominent germinal
centers. The ileum is essentially sterile but the colon has about 750 species of resident
bacteria. The Peyer patches and the vermiform appendix keep colonic bacteria from
spilling into the ileum.
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Slide 55, Colon, H&E
There is a small lymphoid nodule (l) in this specimen. It extends from the lamina propria
into the submucosa. It consists of a small aggregate of lymphocytes, plasma cells, and
macrophages.
Slide 38, Lung, H&E
In the lamina propria of the bronchi (B) and in the scattered CT that holds airways and
blood vessels together, you should easily find small lymphoid aggregates.
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Slide 23, Palatine Tonsil, H&E
This is a specimen of one of the two palatine tonsils, located in the oropharynx on either
side of the root of the tongue. When you stick out your tongue and say “Ahh” you are
exposing the palatine tonsils. They are in essence large collections of lymphoid nodules
(ln) intimately associated with cryptic infoldings of the stratified squamous
unkeratinized epithelium of the oropharynx (ssu). One of the most common pediatric
problems you will encounter is bacterial (often streptococcal) infection of the palatine
tonsils. They are treated with antibiotics and may require tonsillectomy in chronic, severe
cases.
Slide MCW 049, Pharyngeal Tonsil, H&E
This is a specimen of a portion of the pharyngeal tonsil, a complex set of invaginations of
the nasopharygeal epithelium in the upper, median nasopharynx. It is quite similar to the
palatine tonsils, except that it is association with a pseudostratified, ciliated, columnar
(pcc) epithelium with goblet cells, rather than a stratified squamous unkeratinized
epithelium. Children with enlarged pharyngeal tonsils may experience difficulty in
breathing and altered speech. The palatine, pharyngeal, tubal, and lingual tonsils
collectively form a ring of immune tissue that guards the entrance to the esophagus from
the naso- and oropharynx.
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Slide 22, Lymph Node, H&E
This is a section through a lymph node. A thin CT capsule (cp) surrounds the gland. It
has a hilum (h), where an efferent lymphatic or two drains the node. Afferent lymphatics
carry the lymph draining the periphery through the node. The outer cortex (C) has
numerous nodules (n), many with germinal centers. Lymph enters the node through
several peripheral afferent lymphatics, trickles through the subcapsular sinuses, around
and through the cortical nodules, and then along medullary cords (M), to drain out the
hilar efferent lymphatic(s). While slowly percolating through the lymph node, antigenladen lymph is loaded with antibodies by responses in germinal centers.
Slide 25, Lymph Node and Liver, Silver Stain for
Reticular Fibers
The lymph node (LN) is the oval section on the left. The other section is liver (L). We
have already studied the liver and don’t need to concern ourselves with it today. Focus
only on the lymph node during this laboratory session. The thin, black fibers are reticular
fibers. See if you can trace lymph flow from the subcapsular sinuses, across the
germinal centers, along the radial sinuses surrounding trabeculae, along medullary
sinuses to the hilum.
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Slide 24, Spleen, H&E
This is a section through the superficial spleen. The spleen has two main functions:
• Immune surveillance of the blood (white pulp)
• Removal of aged and damaged RBCs (red pulp)
The dense CT capsule (cp) on the left is covered by a mesothelium. Recall that the spleen
is an intraperitoneal organ. Scan along the capsule at intermediate power and see if you
can find a single layer of flattened nuclei. These will be mesothelial cells. This delicate
epithelial capsule is easily damaged so it may not be found everywhere. Scattered
throughout the organ, you will find trabeculae of CT that appear similar to the capsule.
What is their relationship to the capsule? Notice their trabecular arteries (afferents to
central arteries of white pulp) and trabecular veins (drain red pulp). Deep to the
capsule, there are purple/blue areas of white pulp (w) surrounded by red pulp (r). In the
white pulp, you can see periarterial lymphatic sheaths (PALS) with their germinal
centers and central arteries (supplied from trabecular arteries) off to one side of the
PALS. The red pulp looks like a confusing jumble of vascular sinusoids packed with
RBCs. Small branches from the central arteries of the PALS are afferent to the splenic
sinusoids in the red pulp. As red blood cells percolate through this labyrinth of
endothelium-lined sinusoids, aged and damaged RBCs are removed and recycled. Young,
healthy RBCs are collected in veins that drain into trabecular veins and then splenic veins
that exit at the hilum (not shown).
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Review the diagram below to understand basic structure of the spleen. Labels are: C =
capsule, TA = trabecular artery, TV = trabecular vein, WP = white pulp, RP = red pulp,
PALS = periarterial lymphatic sheath, G = germinal center, M = mantle of germinal
center, SC = splenic cord, SS = splenic sinus, CC = closed circulation, OC = open
circulation. Once you have studied this diagram, see if you can trace blood flow through
the spleen.
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Slide 21, Thymus, H&E
The thymus is a grossly lobulated immune organ. Each lobule has an inner, lightly
stained medulla (m) and an outer, darkly stained cortex (c), jam-packed with
lymphocytes. You will not find germinal centers in the thymus. The medulla is rich in
thymic reticular epithelial cells. These secrete proteins that support T-cell
differentiation. These cells form eosinophilic whorls of layered cells called Hassal
corpuscles, a unique feature of the thymus. The cortex of a lobule contains many
lymphocytes and other cell types difficult to identify in this section. As we age, the
population of cortical lymphocytes is gradually depleted and the thymus regresses. Why?
From adolescence on, with increasing age, the incidence of malignant diseases and viral
infections increases. Why?
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URINARY SYSTEM
Objectives
•
•
•
•
•
Identify major structural feature of kidney including cortex and medulla, arcuate
arteries, afferent and efferent arterioles, glomerulus, peritubular capillaries,
medullary rays, and components of nephron.
Identify proximal convoluted tubules (PCTs), distal convoluted tubules (DCTs),
Bowman capsule, loop of Henle, and collecting ducts.
Find components of juxtaglomerular apparatus and review its function.
Be able to trace blood flow through the kidney and relate blood flow to urine
production and flow.
Learn distinctive features of ureter, urinary bladder, and female urethra.
Overview
The most effective way to understand renal function is to learn the blood flow and
urine flow patterns. The renal arteries branch directly from the aorta and carry a massive
blood supply to the kidneys. Blood flows into interlobar arteries, across the arcuate
arteries (at the corticomedullary junction), and then flows rapidly into interlobular
arteries in the medullary rays. As the interlobular arteries ascend toward the superficial
cortex, they send off numerous afferent arterioles that supply cortical glomeruli. A
glomerular filtrate is produced in the glomeruli, and passes into the urinary space. The
glomerular filtrate now passes through the PCT, loop of Henle, DCT, and collecting
tubules. The composition of the glomerular filtrate is gradually changed as it passes
through the nephron, with constituents being mostly removed and returned to the blood
via the peritubular capillary network and vasa recta. In this process, the nitrogenous
wastes are concentrated in urine and excreted down the ureters, to the urinary bladder,
and out the urethra. After processing, blood leaves the branches of the efferent arterioles,
and enters a venous drainage system that essentially mirrors the arterial blood supply of
the kidney. Eventually, blood cleansed of its nitrogenous wastes is returned to the
interlobular veins, arcuate veins, interlobar veins, renal veins, and inferior vena cava.
The juxtaglomerular apparatus consists of three cellular components:
• Juxtaglomerular cells-pressure sensors in wall of afferent arteriole
• Macula densa- urine composition sensors in wall of DCT
• Mesangial cells- that connect these two cell types and provide a communication
link
It is essential for regulating the interplay between blood pressure, glomerular filtration
rate, and urine composition.
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The urinary passages, from the renal pelves, minor and major calyces, ureters,
urinary bladder, and upper portion of the urethra are lined by transitional epithelium and
surrounded by smooth muscle. They are essentially conduits for passive transfer and
active (by smooth muscle contraction) elimination of urine.
Slide 63, Infant Kidney, H&E
This slide shows a lumen (L) of a major calyx along with large blood vessels and adipose
tissue filling the renal sinus. There is about half of a renal pyramid on the left of the
specimen. The cortex (C) and medulla (M) are plainly visible and marked. The renal
papilla is bisected and to the right of the M, many papillary ducts (with tall cuboidal or
low columnar epithelium are obvious. At low power, scan the cortex and note that parts
have radial stripes (pars radiata or medullary rays) and parts consist of many glomerular
and complex jumbles of blood vessels and convoluted tubules (pars convoluta). In the
pars convoluta, increase magnification and find renal corpuscles, glomeruli,
afferent/efferent arterioles (difficult to distinguish), Bowman capsule, PCT, and DCT.
The macula densa of the juxtaglomerular apparatus (JGA) is visible at the vascular
pole of the renal corpuscle. Now scan the medulla and observe the parallel arrays of urine
collecting/processing tubes (loops of Henle) and RBC-filled blood vessels (vasa recta).
Now move to the medulla, where you will be able to see both thin and thick limbs of the
loop of Henle. The ascending and descending limbs of the loop of Henle are similar in
these slides but thin limbs have a squamous epithelium and thick limbs have a cuboidal
epithelium. Make a sketch of this slide and then draw a nephron with a long loop of
Henle in the proper location in your sketch. Now see if you can add blood vessels to your
sketch. Include interlobular arteries, afferent and efferent arterioles, peritubular capillary
network, and vasa recta.
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Slide 62, Adult Kidney, H&E
This slide has most of a renal pyramid from an adult kidney. The renal papilla (rp)
projects into a minor calyx (mc). An interlobar artery branches to an arcuate artery
(aa), which defines the corticomedullary junction (cmj). The cortex (c) and medulla
(m) are clearly labeled. Repeat the drill from the last slide on this slide. Here, the JGA is
much less obvious than in the last slide, so you shouldn’t spend a lot of time searching for
it. When you are finished with these two slides, we expect you to be able to identify the
following structures and understand their relations:
•
•
•
•
•
•
•
•
•
•
•
•
•
Renal corpuscle
Glomerulus
Bowman capsule
PCT and DCT
Loop of Henle
Collecting tubules and ducts
Papillary ducts
Arcuate artery
Medullary rays and interlobular arteries
Afferent/Efferent arterioles (can not be easily distinguished in sections)
Vasa recta
Peritubular capillary network
Juxtaglomerular apparatus
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Slide 64, Ureter, H&E
This is a slightly oblique section through the ureter. Start at low magnification at the
lumen (L) and observe the transitional epithelium. This is a stratified epithelium (5-10
layers of cells) with an apical layer of slightly fatter (“pillowy”) cells bulging a little into
the lumen. There is a loose CT domain beneath the epithelium (no division into mucosa
and submucosa here because there is no muscularis mucosae), followed by indistinctly
arranged, jumbled smooth muscle bundles in the wall. Textbooks describe an inner
longitudinal and an outer circular layer of smooth muscle in the upper ureter, with a third,
outer longitudinal layer being gradually added as you pass down toward the bladder, but
frankly, these arrangements are rarely clear in the ureter and certainly not obvious in this
specimen. What is clear, however, is that this is upper ureter. It is clearly a cross or
slightly oblique section of a tube with an obvious transitional epithelium and a relatively
thin layer of overlapping smooth muscle fibers in the wall. Nothing but ureter in the
human body has this arrangement.
Slide 65, Urinary Bladder, Toluidine Blue
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This is a thin plastic section of the urinary bladder stained with toluidine blue, a basic dye
similar to hematoxylin. This slide is similar to the ureter and can only be distinguished
from ureter because it appears to have a much greater diameter and more robust mural
smooth muscle. You can see the transitional epithelium (te) and several overlapping
layers of smooth muscle (sm) in the muscularis. These bands of smooth muscle basically
follow the curves of the bladder and run in criss-cross fashion. In some regions you can
see one layer running in and out of the plane of section and another layer running more of
less parallel to the plane of section. The mucosa has transitional epithelium that ranges in
thickness between about 5 and 15 cell layers. Because of the thickness of the te, we can
imagine that this bladder was empty when fixed. What happens to the te as the bladder
distends as it fills with urine? There is a slight difference between the denser CT of the
lamina propria and the less dense CT of the submucosa. There is a network of small
arterioles and venules at the mucosal-submucosal junction but no muscularis mucosae.
The adventitia is also quite thick but without a mesothelium. This specimen is urinary
bladder rather than ureter because it is larger than the ureter and has thicker bands of
smooth muscle in the wall.
Slide 75, Urethra/Vagina, H&E
This slide catches a small part of the urethra (U) in section. You can also see a bit of
vaginal epithelium (ve) on the left. This is the lower part of the female urethra and it is
lined by a stratified squamous unkeratinized epithelium, just like the vagina.
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Slide 71, Penis, Monkey, H&E
This slide is a cross section through the penis of a small nonhuman primate. The corpus
cavernosum urethrae (CCU) (aka corpus spongiosum) is a body of erectile tissue that
surrounds the penile urethra. Notice that the penile urethra is lined by an unusual
stratified columnar epithelium. Identify the epithelium in the male urethra but don’t
worry about the rest of the structure in this slide. We will come back to it later in the
course when we study the male reproductive system.
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PITUITARY AND PINEAL GLANDS
Objectives
•
•
•
Learn basic microscopic anatomy of pituitary and pineal glands
Be able to identify acidophils, basophils, chromophobes, pituicytes, and
pinealocytes
Relate structural features to functional features of these two glands
Overview
The pituitary gland (hypophysis cerebri) lies at the base of the brain adjacent to
the third ventricle. It rests in a recess of the sphenoid bone called the sella turcica. It has
two main components, a neurohypophysis (NH) and an adenohypophysis (AH). The NH
is a peduncle of CNS tissue. It has two main functions: 1) regulation of AH function
through releasing hormones; and, 2) synthesis and secretion of oxytocin and ADH. Some
authors include the hypothalamic supraoptic and paraventricular nuclei in the
neurohypophysis. Conversely, the median eminence is often viewed as part of the
hypothalamus. For simplicity, we will define the NH as median eminence, infundibular
stem, and infundibular process (pars nervosa). The AH consists of the pars tuberalis, pars
intermedia, and pars distalis. NH releasing hormones are carried from the NH to the AH
by a hypothalamohypophyseal portal system. When they arrive at the AH, they trigger
release of hormones, from the AH’s basophils and acidophils, into the systemic
circulation. The important features of the pituitary gland are shown in the following
diagram:
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Legend- yellow = neurohypophysis, purple = adenohypophysis, IIIV = third ventricle, PV
= paraventricular nucleus, SA = supraoptic nucleus, OC = optic chiasm, ME = median
eminence, HH = hypothalamic-hypophyseotropic area, PS = infundibular stem, rest of
yellow lobe = infundibular process (pars nervosa), tuberalis = pars tuberalis, intermediate
lobe = pars intermedia, rest of purple blob = pars distalis
The pineal gland (epiphysis cerebri) sits on top of the brain and is surrounded by a
thin extension of the pia-arachnoid meninges. It contains pinealocytes (modified neurons)
and glial cells, mainly astrocytes. Pinealocytes synthesize and secrete melatonin, a
polypeptide that regulates our circadian rhythms.
140
Slide 90, Pituitary Gland, H&E
This slide has a large piece of neurophypophysis (NH), specifically the infundibular
process, a small amount of adenohypophyseal pars intermedia (PI), and a large portion
of adenohypophyseal pars distalis (PD). Start with the NH at intermediate
magnification. It contains many nerve fibers. These are the unmyelinated axons of
neurons whose cells bodies are in the supraoptic and paraventricular nuclei of the
hypothalamus. In addition, there are many nuclei of pituicytes. These are supportive glial
cells. Capillaries are also abundant here. Now study the pars distalis at intermediate
power. You can see many darkly stained epithelial cells arranged in plates, cords, and
follicles. The reddish cells are the acidophils and the purplish cells are the basophils.
These two basic cell types are much more distinct in the next slide. There are also
numerous poorly stained chromophobes. Surrounding these adenohypophyseal cells,
there is a delicate CT network supporting a rich plexus of capillaries. Now go on to the
next slide to get a clearer view of acidophils and basophils.
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Slide 90A, Pituitary Gland, Mallory Stain
This slide has been stained with Mallory stain. Mallory stain contains a mixture of dyes.
The neurohypophysis (NH) is light blue and adenohypophysis (AH) is much darker,
with areas where bluish cells or orange-red cells predominate. At lowest power, notice
that the upper left half of the AH is bluer and the lower right half is redder. Now go to
intermediate power and study the AH. Basophils stain several shades of blue in this slide.
These tinctorial differences reflect different concentrations of basophil hormones in the
cytoplasm or in follicles. Notice that you can find follicles filled with blue secretion and
these are surrounded by lighter blue basophils. Acidophils stain several shades of
red/orange. Some are orange. Others are redder, perhaps brick red. As you move from
one area to another, notice that different regions of the AH have different ratios of
basophils to acidophils. Numerous chromophobes are common. They are pale and
agranular. In the AH, the delicate collagen fibers are stained blue. Capillaries are
ubiquitous.
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Slide 91, Pineal Gland, H&E
This slide has many intensely basophilic blobs scattered everywhere. These are the
corpora arenacea (CA) (brain sand). Basically the pia-arachnoid meninges surround
the gland in a capsule. Parts of this are visible. Projections from the capsule deep into the
gland divide it into inconspicuous lobules. At higher magnification, you can see jumbled
masses of nerve processes, rounder nuclei (pinealocytes), and polygonal nuclei (glial
cells) as well as capillaries everywhere.
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THYROID, PARATHYROID, AND ADRENAL GLANDS
Objectives
•
•
•
•
•
Learn basic microscopic anatomy of thyroid gland, parathyroid gland, and adrenal
gland.
Be able to identify thyroid follicular epithelial cells, C-cells, and perifollicular
capillaries.
Be able to identify chief and oxyphils cells in parathyroid glands.
Locate adrenal cortex and medulla and understand structural/functional zonation
of adrenal cortex.
Learn to discriminate between these important endocrine glands.
Overview
Endocrine glands secrete into the blood. Thus, they are richly supplied with
fenestrated capillaries. Their epithelial cells synthesize and store hormones, which are
released from the cells of the glands usually as a result of stimulation from the pituitary
gland. The active hormones secreted by these glands are amino acids (thyroxine from
thyroid gland), proteins (parathormone from parathyroid glands), steroids (cortisol from
adrenal cortex), or catecholamines (epinephrine from adrenal medulla).
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Slide SL029, Thyroid Gland, H&E
This is a slide of the thyroid gland. Scan it at low power and notice that there are
numerous spherical follicles, lined by thyroid follicular epithelial cells. Note that these
cells range in height from low simple columnar in empty follicles, to simple cuboidal in
filling follicles, to simple squamous in filled follicles. The pink material in the middle of
follicles is thyroid colloid, a concentrated aqueous solution of mainly thyroglobulin.
Between the follicles, there is a sparse CT domain with a few fibroblasts and collagen
fibers, supporting a network of fenestrated capillaries that surround all follicles. The
calcitonin-secreting C-cells (parafollicular cells) are not easily found on this preparation.
They are located at the edges of follicles or in small clusters in the CT. They are large,
ovoid cells with a pale-staining cytoplasm. Here is what they would look like in a wellfixed, well-stain specimen (pale cells to the left of C are parafollicular (C-) cells:
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Slide 89, Parathyroid Gland, H&E
If you look almost anywhere in this slide at high magnification, you will see clusters of
mostly purplish, basophilic, faintly granulated chief cells. These secrete parathormone
into the fenestrated capillaries surrounding the epithelial cords and plates of chief cells.
Here and there, you will also find small clusters of larger eosinophilic cells with smaller,
more heterochromatic nuclei. These are oxyphils. The CT surrounding the chief cells and
oxyphils has a few fibroblasts, variable numbers of adipocytes, and numerous blood
vessels.
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Slide 86, Adrenal Gland, H&E
The adrenal glands are really two completely separate glands, an adrenal cortex (C) on
the outside surrounding an adrenal medulla (M) down the middle of the gland. Central
veins (V) drain the medulla. Start at intermediate magnification at the superficial edge of
the cortex. You will be able to distinguish the three cortical layers, outer zona
glomerulosa, middle (thickest) zona fasciculata, and inner zona reticularis. Notice the
abundance of capillaries surrounding the steroidogenic cortical tissue. These are
particularly clear in the zona fasciculata. The boundary between the zona reticularis and
the medulla is hard to identify. Once clearly in the medulla, you will be able to find
numerous large, granulated cells. These are the chromaffin cells of the adrenal medulla.
Although not clearly distinct in this specimen, one population of chromaffin cells secretes
epinephrine (adrenalin) and the other secretes norepinephrine (noradrenalin). Careful
study of the adrenal medulla may reveal a few sympathetic nerve fibers. These
innervate the chromaffin cells (really modified sympathetic postganglionic neurons) and
cause, e.g., sudden discharge of epinephrine for fight-or-flight reactions.
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EYE AND OCULAR ADNEXA
Objectives
•
•
•
•
•
Learn basic anatomy of eye, all three tunics
Study how sclera and cornea differ.
Learn details of ciliary body, iris, limbus, and drainage system for aqueous humor
and nonreceptive retina (over ciliary body and posterior surface of iris)
Learn 10 layers of receptive retina
Study optic nerve, eyelid, and lacrimal gland
Overview
The eye has three tunics. The outer sclera is an opaque, fibrous capsule
posteriorly and clear cornea anteriorly. The middle tunic is the uvea and includes the
choriocapillary layer posteriorly, the ciliary body in the middle, and the iris anteriorly.
The uvea (choroids) contains numerous capillaries, some CT, and pigment. It provides
part of the blood supply to the pars nervosa retinae (choriocapillary layer), produces
aqueous humor in the ciliary body, and forms most of the body of the iris. The inner
ocular tunic is the retina. The retina covers the posterior surface of the iris (pars iridica
retinae), the ciliary body (pars ciliaris retinae), and posterior to the ora serrata (pars
nervosa retinae) contains rods and cones and other neurons. The lens is an important
refractile medium of the eye and divides the eye into an anterior and posterior chamber.
Aqueous humor fills the anterior chamber, which lies between the lens and the corneal
endothelium. The vitreous body fills the posterior chamber, which lies between the lens
and the neural retina.
The pars nervosa retinae has 10 layers that should be observed, studied, and
learned in this laboratory. Light strikes the outer limiting membrane first, passes through
the optic nerve fiber layer, the ganglion cell layer, the inner plexiform layer, the inner
nuclear layer, the outer plexiform layer, the outer nuclear layer, and the rod and cone
outer segments. In the outer segments of the photoreceptors, light generates electrical
signals that are then conveyed to the optic nerve. Signals go from the rods and cones via
axons back toward the ganglion cell layer and leave the eye via the optic nerve, which
consists mainly of axons of ganglion cells and glial cells such as oligodendroglia and
astrocytes.
The ocular adnexa include the eyelids and lacrimal glands. These structures
protect, lubricate, and clean the cornea to permit vision.
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Slide 78, Complete Eyeball, H&E
Use this slide to study the three tunics of the eye. Start with the outer tunic. The limbus is
the junction between the cornea and the sclera. The sclera contains many layers of dense
irregular CT with many fibroblasts and collagen fibers but few blood vessels, except at
the limbus. The cornea (C) is completely transparent and avascular. The cornea functions
as the primary refractive structure of the eye, allowing images to focus on the neural
retina. The tear film maintains the smooth corneal surface. Corneal clarity depends upon
highly ordered packing of stromal collagen fibrils and careful regulation of hydration by
corneal endothelial cells. It consists of five layers from anterior to posterior:
(1) Corneal epithelium- a stratified squamous unkeratinized layer continuous with
the conjunctiva and eventually the skin on the eyelid.
(2) Bowman membrane- the basement membrane of the corneal epithelium and
associated collagen fibers
(3) Corneal stroma- consists of several regular layers of collagen fibers overlapping
orthogonally with interspersed fibroblasts
(4) Descemet membrane- basement membrane of corneal endothelium and
associated extracellular matrix
(5) Corneal endothelium- a simple squamous epithelium that also covers the
trabecular meshwork and canal of Schlemm.
Light passes through the pupil (P), a hole in the iris and strikes the lens (L), which is
suspended from the ciliary body (CB) by thin tubular cables called the ciliary zonules.
The fixed lens is extremely fragile and is broken (a sectioning artifact). At the edges of
the lens, you can find the nuclei of lens fibers. There is also a simple cuboidal epithelium
on the anterior surface of the lens. The posterior surface of the lens consists of elongated
lens fibers. After passing through the lens, light crosses the vitreous body (VB). This is a
peculiar CT, mostly water and rich in hyaluronic acid, but with a few cells and fibers,
visible as faint lines just posterior to the lens.
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Now study the choroid in the posterior portion of the eye. The choroid has a thick layer of
pigment derived from melanocytes and some fibroblasts and extracellular fibers inside
the layer of pigment. There are few capillaries visible in this specimen. The Bruch
membrane, a composite structure formed by the basement membrane of the pigmented
retinal epithelium and adjacent fibers, is scarcely visible.
The pars nervosa retinae in this specimen is well preserved and shows most of the ten
layers described in lecture and your atlas. Starting at the outer most part of the retina,
adjacent to the choroid layer, you will see a thin, pigmented layer. This is the pigmented
retinal epithelium (1). Moving in toward the vitreous body, you can see outer rod and
cone segments (2) and traces of the outer limiting membrane (3). As you move more
toward the vitreous body, you will see the outer nuclear layer (4), the outer plexiform
layer (5), the inner nuclear layer (6), the inner plexiform layer (7), ganglion cell layer
(8), optic nerve fiber layer (9), and inner limiting membrane (10). In the lower right
corner of the specimen, you can see an area made exclusively of optic nerve fibers. This
is the optic papilla. At the optic papilla, optic nerve fibers exit the eyeball and enter the
optic nerve. Branches of the central retinal artery will also be evident here. As you travel
along the pars nervosa retinae toward the ciliary body, you will encounter an area where
the inner layers of the retina suddenly transition over to a single, unpigmented layer of
cells. This is the ora serrata, marking the end of the pars nervosa retinae and the
beginning of the pars ciliaris retinae. We will study the ciliary body and iris in more
detail in the next slide.
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Slide 97, Anterior Eyeball, H&E
For orientation, your specimen has been labeled. The cornea (C), anterior chamber
(ac), lens (L), and ciliary muscle (cm) should be located. The arrow marks the limbus
(corneoscleral junction). Now study the ciliary body. The ciliary muscle contains
numerous smooth muscle fibers. It contracts for focusing on near objects, releasing
tension of ciliary zonules and allowing lens to become fatter, more convex, and thus
having a shorter focal length. The ciliary processes are complex folds in the ciliary body.
They have many small capillaries surrounded by a thin sheath of CT and covered by the
pars ciliaris retinae, which consists of an outer pigmented layer and an inner
unpigmented layer. The unpigmented cells are responsible for producing a filtrate of the
blood in the capillaries, the aqueous humor. Aqueous humor nourishes the lens and
cornea (both avascular) and eventually drains from the anterior chamber through the
trabecular meshwork and canal of Sclemm (near the limbus), both visible in the
sulcus formed by the junction of the cornea and iris.
Now study the iris. It consists of dense CT with embedded smooth muscle, the dilator and
sphincter of the pupil. It is richly pigmented by melanocytes. Differences in eye color are
reflections of differing amounts of iridial pigment, with brown eyes having most pigment,
hazel eyes having an intermediate amount, and blue eyes having the least. The anterior
iridial surface has no epithelial covering, an unusual circumstance for a free surface in the
human body. Can you think of another free surface without an epithelial covering facing
a fluid-filled cavity? The pars iridica retinae covers the posterior surface of the iris. This
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was once a two-layered structure, early in development. The outer layer dispersed into
the body of the iris and differentiated into pupillary smooth muscle, an unusual example
of smooth muscle derived from ectoderm. The outer layer of the pars iridica retinae
(forming smooth muscle) is homologous to the outer pigmented layer of the pars ciliaris
retinae and the pigmented retina epithelium (layer 1) of the pars nervosa retinae. The
inner layer became pigmented; thus, a single layer of pigmented epithelium covers the
posterior surface of the iris. This single layer of pigmented epithelium is continuous with
the unpigmented epithelium of the pars ciliaris retina and layers 2-10 of the pars
nervosa retinae posterior to the ora serrata.
Slide 96, Optic Nerve and Pars Nervosa Retinae, H&E
On the left, there is a cross section of the optic nerve (ON). On the right, there is a cross
section through the pars nervosa retinae (R). Start with the optic nerve and observe the
numerous blood vessels, carrying blood to and from the retina and the bundles of axons.
These represent myelinated nerve fibers that project away from the ganglion cells toward
the brain. Myelination begins immediately after the axons from the ganglion cells exit the
back of the eyeball at the lamina cribrosa. The retina and optic nerve are part of the
central nervous system. Therefore, the myelinating cells present in the optic nerve are
oligodendroglial cells, not Schwann cells. The CT-like cells that bundle axons into
groups and support blood vessels are astrocytes. There are also a few microglial cells
present here. You will see many nuclei in the optic nerve but may not be able to easily
distinguish the different kinds of glial cells present. The optic nerve is surrounded by
dura matter and the pia-arachnoid and is bathed in cerebrospinal fluid, just like the rest of
the CNS.
Now examine the pars nervosa retinae. There is a lot of sclera and choroid included in
this specimen (on the right). The split in the section is an artifact, as are the pink folds in
the retina that run perpendicular to the plane of the retina. Start at the left side of the
specimen at intermediate magnification and study the layers of the retina carefully.
Identify all 10 layers of the pars nervosa retinae. The only layer of the retina that is
sketchy in this specimen is the outer limiting membrane. This is basically a line of tight
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junctions between the rods and cones and Müller cells, the main retinal glial cells. Müller
cells have their nuclei in the inner nuclear layer along with the nuclei of bipolar cells.
Careful inspection of the inner nuclear layer reveals many round, lightly stained nuclei
(bipolar cells) and a few polygonal, darkly stained nuclei (Müller cells). Realize that the
Müller cells extend across the entire thickness of layers 2-9 of the retina. Their basal
surface rests on the inner limiting membrane (the basement membrane for the neural
retina) and their apical surfaces have tight junctions with the rods and cones (to form the
outer limiting membrane) and microvilli projecting between the outer segments of rods
and cones, nearly to the pigmented retinal epithelium (layer 1). The Müller cells
synthesize and secrete proteins that make up both the ILM and OLM so they play a key
role in maintaining the organization of cells within the retina. Naturally, this is not
evident in your specimens but has been clearly described using the electron microscope.
A good way to test your understanding of the retina is to draw a wiring diagram of it and
indicate the boundaries of the 10 layers.
There is a potential space between layers 1 and 2, the intraretinal space. This space was
once continuous with the ventricles of the brain. Remember your embryology of the eye.
It is here that the pigmented retina (derived from outer layer of optic cup) and neural
retina (derived from inner layer of optic cup) are apposed apex to apex to one another.
The pigmented retinal epithelium has deep apical recesses that receive the outer segments
of the rods and cone (really modified cilia- a typical apical epithelial projection). Because
epithelia are always apically nonadhesive, the potential intraretinal space can become an
actual space. A traumatic blow to the head can cause retinal detachment. This can result
in separation of the neural retina from the blood supply derived from the choriocapillary
layer, and, if not repaired, can lead to permanent death of the neural retina and blindness.
Notice that there are blood vessels on both the inner surface of the retina (branches of the
central retina artery) and adjacent to the outer layers of the retina, in the choriocapillary
layer (much more obvious in this slide than in Slide 78. The photomicrograph below is a
well-fixed, labeled example of the entire thickness of the pars nervosa retinae, the
choroid, and part of the sclera, oriented like your specimen:
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Legend S = sclera, C = choroid, 1= pigmented retinal epithelium, 2 = outer segment of
photoreceptors, 3 = inner segment of photoreceptors, 4 = outer nuclear layer, 5 = outer
plexiform layer, 6 = inner nuclear layer, 7 = inner plexiform layer, 8 = ganglion cell
layer, 9 = optic nerve fiber layer, 10 = inner limiting membrane. Notice the large blood
vessel in the lower left. This is a branch of the central retinal artery. There are also
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numerous blood vessels in the choroid. In the next illustration, I have sketched in some
important landmarks and a simplified wiring diagram of the retina for your information.
Legend abbreviations for this diagram include: RPE = pigmented retinal epithelium, IRS
= intraretinal space, ROS = rod outer segments. The green dotted line is the basement
membrane for the neural retina, the inner limiting membrane. The red dotted line is the
basement for the RPE, the Bruch membrane. Notice how the blue Müller cell has its
nucleus and cell body in the inner nuclear layer, a basal process on the inner limiting
membrane, and an apical process extending up to the outer limiting membrane. The
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orange arrow shows the direction of light and the red arrow shows the direction of
electrical signals generated in response to incident light. In this simplified diagram, which
does not show amacrine and horizontal cells, there are essentially three layers of cells, the
photoreceptors (here shown as a yellow rod), the bipolar cells (green) and the ganglion
cells (red) in the neural retinal.
Our slide collection does not have a good example of the fovea centralis. This is the
place in the retina where we have maximal visual acuity. It contains only cones, but these
cones have elongated rod-like outer segments that are densely packed together to form a
high-resolution matrix of photoreceptors. In addition, retinal layers 5-9 are thinned and
pushed off to the side, creating a significant depression. Recall that incident light strikes
layer 10 first and layer 1 last, so in the region of maximal visual acuity, much of the
retinal structure that would scatter light and decrease acuity is pushed off to the side. A
good example of the fovea centralis is shown below. In this diagram, the light vector goes
from top to bottom of the picture.
We also lack a good example of the optic papilla, so one is included for your edification.
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Notice that there are no rods and cones in the middle of the papilla. This is the blind spot
of the eye. Here, about 1,000,000 axons of ganglion cells are bundled, exit the eyeball
through the sclera, and form the optic nerve (bottom of photo).
Slide 87, Eyelid, H&E
The outer surface of the eyelid is covered by thin skin (TS). The opposite side has
palpebral conjunctiva (C). On the conjunctival side, there is a dense band of CT, the
tarsal plate (TP), with embedded meibomian glands (MG). These are highly elaborated
sebaceous glands that produce the lipid component of the tears and they are associated
with hair follicles containing the eyelashes (EL). There is also a large amount of skeletal
muscle present, the levator palpabrae (LP) (raises eyelids) and orbicularis oculi (closes
eyelids). The conjunctival epithelium is a stratified squamous unkeratinized layer only
two or three cell layers thick, which gives over to thin skin at the margin of the eyelid.
This epithelium contains goblet cells; these make the mucous component of the tear film.
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Slide 93, Lacrimal Gland, H&E
The lacrimal glands produce the aqueous component of tears. They are located in the
superior-lateral part of the orbit and open into the conjunctiva by way of numerous ducts.
It is a compound tubuloalveolar gland with serous acini. The acinar cells appear faintly
granular because they contain granules of glycoproteins. The smaller ducts are lined by
simple cuboidal epithelium and the larger ducts are lined by stratified cuboidal
epithelium. Contractile myoepithelial cells surround some acini. The lacrimal gland most
resembles the parotid salivary gland but can easily be distinguished from it in side-byside comparisons:
•
•
•
Lacrimal gland is less lobulated, parotid gland is more lobulated
Lacrimal gland ducts less obvious, parotid gland ducts more obvious
Lacrimal gland has faintly stained acinar granules, parotid acinar zymogen
granules stain darkly
See Slide 44 in next lab for comparison.
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AUDITORY SYSTEM
Objectives
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Learn histological structure and function of auricle and external auditory meatus
Learn the detailed microscopic anatomy of the membranous labyrinth of the inner
ear, study the organ of Corti and macula, and learn the relationship between the
membranous labyrinth and the bony labyrinth.
Locate mechanoreceptors and supportive cells in organ of Corti and macula and
relate their structure to auditory and vestibular function.
Overview
The auditory system has three main components: 1) outer ear, 2) middle ear, and
3) inner ear. The outer ear includes the auricle (pinna) and external auditory meatus. The
middle ear extends from the tympanic membrane to the inner ear and has a component
that extends into the nasopharynx (auditory or eustachian tube). The inner ear is a
complex closed vesicle (the membranous labyrinth) enclosed within the bony labyrinth, a
complex hole in the petrous temporal bone. In most places, the membranous labyrinth is
lined by a simple squamous epithelium. However, in six patches, the lining of the
membranous labyrinth is modified to form hair- and supportive-cell-rich, innervated
neuroepithelium. These six patches of neuroepithelium include one organ of Corti (for
sound perception), three cristae ampullares (for detection of changes in angular
momentum of the head) in the three semicircular canals, and two maculae (for detection
of changes in inertia of motion) in the utricle and saccule (1 + 3 + 2 = 6). The key cells
of the membranous labyrinth are the hair cells. These have apical modifications (kinocilia
(modified cilia) and/or stereocilia (modified microvilli) that converted motion into
electrical activity (mechanoreceptors or mechanical transducers).
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Slide 35, Auricle (Pinna), Elastic Stain
This slide is a portion of the auricle (pinna) stained with the elastic stain. It contains a
large piece of elastic cartilage (EC) in the middle. This maintains the peculiar shape of
the pinna so that it can gather and amplify sound. The pinna is covered by thin skin with
a few hair follicles and a few eccrine sweat glands.
Slide 98, External Auditory Meatus, Transverse
Section, H&E
The external auditory meatus (EAM) begins at the pinna and ends at the tympanic
membrane. It is surrounded by several pieces of hyaline and elastic cartilage (C). The
external auditory meatus is lined with thin skin with hair follicles, sebaceous glands, and
characteristic ceruminous glands (G). These are modified apocrine sweat glands. They
have ducts lined by a stratified cuboidal epithelium and acidophilic acini with distended
lumina. They secrete cerumen (ear wax).
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Slide 99, Cochlea, H&E
This is a complex section that includes the modiolus (M), a spiral of bone. The cochlear
nerve (CN) is at the base of the cochlea. This is part of which cranial nerve? You will be
able to find the spiral ganglion in the modiolus. The scala media (sm) is associated with
a scala vestibuli and scala tympani, both of which are joined together at the
helicotrema (H). To the right, there is a large cavity, the vestibule (V) and an associated
portion of the macula sacculi (Mac). Once you have used your class notes and atlas to
become oriented to this slide, find the macula and locate hair cells, supporting cells, the
otolithic membrane, and otoliths. Now you should study the organ of Corti carefully
by going to the scala media (cochlear duct) labeled on your specimen. In your specimen,
be sure to locate the following structures:
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•
•
•
•
Vestibular and basilar membranes
One row of inner hair cells and three rows of outer hair cells and their
supporting phalangeal cells
Tectorial membrane
Stria vascularis
Inner tunnel and pillar cells
Although not clearly visible in your slides, nerve fibers from the spiral ganglion travel
along the basilar membrane, penetrate it, and synapse with the hair cells. Deformations of
the hair cells (as they move against the fixed tectorial membrane) generate action
potentials that are conducted centrally and perceived by the brain as sounds. What is the
function of the stria vascularis? Where on your slide are hair cells with maximal
sensitivity to low frequency sounds and high frequency sounds?
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Slide MCW217, Crista Ampullaris and Cochlea, H&E
This slide includes a portion of the sensory neuroepithelium in one of the three
semicircular canals, called the crista ampullaris (Cr). The three cristae ampullares,
oriented in the three planes of space, detect changes in angular momentum of the head.
When angular momentum of the head changes, the endolymphatic fluid sloshes around,
moves the cupula, and deforms the steroeocilia toward the kinocilium on the apices of the
hair cells. Because the the mechanically gated ion channels in the membranes of the
stereocilia, action potentials are generated in the hair cells and conveyed back to the
brain. Locate this structure at low power and then at 40X. Find the cupula (pink,
acellular, homogeneous-the extracellular matrix into which the kinocilia and stereocilia
of the hair cells are embedded), hair cells (apical, lightly stained, ovoid cells), and
supporting cells (basal, darkly stained, pyramidal cells). Nerve fibers synapsing with the
hair cells convey impulses into the vestibular branch of CN VIII. You also have several
turns of the cochlea in this slide. This is a good place to re-examine the organ of Corti.
Get oriented using an atlas.
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FEMALE REPRODUCTIVE SYSTEM
Objectives
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•
•
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Study ovarian structure and function, learning different stages of follicular
development, differentiating between developing and atretic follicles, and
understanding corpus luteum and corpus albicans.
Understand basic morphology of the uterine tubes and their regional variation.
Understand basic morphology of uterus and be able to distinguish between
proliferative and secretory phases.
Study structure and function of cervix and vagina
Understand basic morphology of term placenta
Overview
The ovary is an essential organ in the female reproductive system. It contains
developing follicles, the source of hormones that regulate the menstrual cycle in the rest
of the female reproductive system. It also is a source of ova, female gametes. Once
released from the ovary, a secondary oocyte—(remember, meiosis is not completed if and
only if fertilization occurs)—and its associated structures is captured by the fimbria of the
uterine tubes and transported proximally through the uterine tubes, by ciliary beating and
peristalsis, to the uterus. Fertilization occurs in the uterine tubes. The conceptus (name
given to early pre-embryo) enters the uterus and becomes attached to the endometrium
during implantation. The conceptus now becomes a pre-embryo and begins to secrete
human chorionic gonadotrophin (hCG). This hormone stimulates persistence of the
corpus luteum so that menstruation does not occur. If there is no fertilization, no preembryo, and therefore no hCG, the corpus luteum regresses and menstruation ensues.
The most effective and functionally memorable approach to learning the female
reproductive cycle is to realize that preovulatory events, driven by estrogen from the
developing follicle, prepare the endometrium for receiving a conceptus (glands
proliferate), and postovulatory events, driven by progesterone from the corpus luteum,
produce trophic secretions (glands secrete) to support the conceptus.
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Slide 81, Ovary, H&E
The ovary has a superficial cortex (C) with follicles in many different stages of
development and a deep medulla (M) with stromal CT elements and large blood vessels.
Using intermediate magnification, start at the edge of this specimen anywhere and
observe a thin CT capsule called the tunica albuginea. In some locations, you may be
able to see a simple cuboidal epithelium covering the tunica albuginea. This is the
germinal epithelium. This is the mesothelium covering the ovary. In all other locations,
this mesothelium is a simple squamous layer but over the surface of the ovary, it is
cuboidal rather than squamous. This is an anatomical factoid of unknown functional
significance. The tunica albuginea gives way to a dense field of CT called the stroma,
with numerous embedded cortical follicles. The most superficial and smallest follicles are
the primordial follicles. These consist of a simple squamous layer of follicular epithelial
(granulosa) cells surrounding an oocyte. As granulosa cells proliferate, they form several
layers surrounding the oocyte. A follicle with several layers of granulosa cells but
without an antrum is a primary follicle. Now granulosa cells secrete glycoproteins that
accumulate in an eccentric cavity called the antrum. Once a follicle has an antrum it is a
secondary follicle. In each menstrual cycle, about 5-10 follicles in each ovary begin as
primordial follicles and grow rapidly to become large secondary (antral) follicles. One of
this group becomes a dominant follicle and ends up being ovulated. The rest begin to
degenerate and become atretic follicles. Most of the large follicles in your section are
atretic secondary follicles. In atretic follicles, the granulosa cells are only loosely
adherent to one another and their nuclei exhibit pyknosis, i.e., they are condensed,
smaller, and heterochromatic (darkly stained). Pyknotic nuclei are found in necrotic
tissue. In some secondary follicles, you may be able to find oocytes surrounded by a
zona pellucida and contained within a shell of granulosa cells called the cumulus
oöphorus.
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Slide 82, Ovary with Corpus Luteum, H&E
This is a portion of an ovary with a large corpus luteum (CL). The corpus luteum is the
progesterone-secreting remnant of an ovulated mature secondary (antral, graafian)
follicle. Down and to the left of the corpus luteum, there is other ovarian tissue with
several stages of follicular development evident in the cortex. To the right, there are
several sections through helicine arteries and veins. Most of the cells in the corpus
luteum are granulosa lutein cells. These result from the luteinization of granulosa cells
after ovulation. They have large euchromatic nuclei with nucleoli and an acidophilic,
faintly granular cytoplasm. Among the granulosa lutein cells, there are also numerous
capillaries. The theca lutein cells arise from the theca interna. They are smaller than
granulosa lutein cells and form denser boundaries between collections of granulosa lutein
cells.
Slide 83, Uterine Tube, H&E
This is a section through the ampullary portion (distal) of the uterine tubes. The lumen
(L) of the uterine tube is labeled. Notice the elaborate mucosal folds (MF). The mucosal
epithelium is simple columnar with a mixture of ciliated cells and secretory (peg) cells.
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The ciliated cells beat proximally and propel luminal contents (including the conceptus)
toward the lumen of the uterus where implantation will occur. The secretory cells secrete
poorly characterized growth factors that probably support early development of the
conceptus. You will easily be able to see primary, secondary, and tertiary mucosal folds.
There is also a thick wall consisting of smooth muscle (SM) in indistinct layers. With a
bit of imagination, you can see that the inner fibers are more or less predominantly
circular and the outer fibers are more predominantly longitudinal, although fibers run in
both directions throughout the entire mural thickness.
Slide 84, Uterine Tube, H&E
This is also from the ampullary portion of the uterine tubes. In this thin plastic section,
the distinction between ciliated and secretory mucosal epithelial cells is easily made. The
arrangement of smooth muscle into an inner circular and an outer longitudinal layer is
clearer.
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Slide SL021, Proliferative (Preovulatory) Uterus, H&E
The uterus has three layers, an endometrium (E) facing the lumen (at the top), a
myometrium (M) in the middle, and a perimetrium (outer CT capsule-not show on this
slide). The endometrium consists of deep surface invaginations (glands) lined by a
simple columnar epithelium with a few ciliated cells and many secretory cells. The
glands are supported by a thick lamina propria called the endometrial stroma with
numerous blood vessels. The superficial portion of the endometrium is sloughed during
menstruation and is called the lamina functionalis. The deep portion, with glands
penetrating into the superficial myometrium, is retained during menstruation and is called
the lamina basalis. Following menstruation, a new functionalis is regenerated from
remnants of the basalis. In this proliferative (preovulatory) endometrium, notice that
the glands are slightly twisted and have narrow lumina without much secretory material
in them. Search around in glandular epithelium to see if you can find mitotic figures. The
myometrium is a thick layer with criss-crossing smooth muscle fibers held firmly
together by a dense CT domain and numerous blood vessels.
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Slide 73, Secretory (Postovulatory) Uterus, H&E
This secretory (postovulatory) uterus is similar to the last slide in most respects, but the
endometrium (E) is thicker. The endometrial glands are deeper, more tortuous, and
have dilated lumina with accumulations of secretions in the glands. There are fewer
mitotic figures than in the last slide. The blood supply of the endometrial stroma is also
richer than the last slide. In addition, the division between myometrium (M) and
perimetrium (P) is clearer. The boundary between these two layers is gradual, but you
will know you are in perimetrium when you notice that the CT dominates this layer as
compared to myometrium, which has abundant smooth muscle.
Slide 74, Cervix, H&E
This section passes parallel to the cervical canal. The smooth muscle (SM) in the wall has
both circular and longitudinal elements. The ectocervix (Ec) is continuous with the
vagina and is lined by a stratified squamous, unkeratinized epithelium that undergoes a
sudden transition to simple columnar epithelium of the endocervix (EnC) at the ostium
uteri. The endocervix has numerous deep tortuous folded clefts called the plicae
palmatae lined by simple columnar cells that secrete mucus. The physical and chemical
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characteristics of cervical mucus change during the female reproductive cycle. For
example, at midcycle, when ovulation occurs, it has a viscosity that is particularly
amenable to sperm penetration. During pregnancy, it forms a semi-solid mucus plug that
prevents vaginal bacteria from entering the uterus.
Slide 85, Vagina, H&E
The vaginal mucosa (vm) has a stratified squamous unkeratinized epithelium
covering a loose, richly vascularized lamina propria. There is no clear boundary
between the mucosa and the submucosa and there is a lot of smooth muscle and CT in the
muscularis. It may be possible to find skeletal muscle fibers here as well. Notice that the
vaginal mucosa has no glands and many blood vessels. During sexual activity, vaginal
lubricants come from the Bartholin (vestibular) glands and transudates from blood
vessels in the vaginal mucosa. Lack of glands is an important feature to distinguish the
vagina from the esophagus.
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Slide 75, Vagina and Urethra, H&E
This slide is quite similar to the last slide, except that it has a part of the urethra (U) in it.
Examine the vaginal epithelium (ve) and recognize that it is stratified squamous
unkeratinized epithelium. What kind of epithelium lines the urethra?
Slide 80, Term Placenta, H&E
This is a section from the margin of a normal delivered placenta. The upper surface is
covered by a cuboidal epithelium of the amnion (a). Basically, the placenta has two
tough, fibrous connective tissue layers, one the chorionic plate (CP) where the umbilical
cord inserts (not in this specimen), and, the other, the basal plate (BP), which is pressed
firmly against the endometrium of the uterus. There is a layer of fibrous, acidophilic
protein called fibrinoid deposit (Nitabuch membrane), which covers the basal plate.
Especially in the basal plate, but scattered throughout the chorionic plate as well, you can
see a broken layer or two of basophilic cells with large nuclei. These are decidual cells.
Most of the placenta is fetal tissue, but the decidual cells, which are shed with the
placenta at parturition, are derived from endometrial stroma and are therefore maternal
cells. The chorionic and basal plates are joined at the margin and are connected by
numerous cytotrophoblastic cell columns (ccc). Placental villi project from the
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cytotrophoblastic cell columns into the intervillous space (ivs), which contains maternal
blood. In a working placenta, the intervillous space would be jammed with maternal
RBCs.
Just prior to separation of the placenta, the uterine arteries that penetrate the basal plate
and squirt oxygenated maternal blood into the intervillous space become constricted, so
that the perfusion of the ivs decreases. That is why there are so few maternal RBCs in the
ivs in this slide. Now, at high magnification, examine a villus in cross section. You will
see numerous capillaries, filled with fetal blood. Notice that these capillaries are pressed
close to the edge of the villus. There is a thin layer of syncytiotrophoblast at the
maternal/fetal interface. In the term placenta, the cytotrophoblast is a thin, discontinuous
layer beneath the syncytiotrophoblast. Earlier, these proliferative cells from a continuous
layer, but by term, they have almost all been converted to syncytiotrophoblast.
Deoxygenated fetal blood comes to the placenta through a pair of umbilical arteries.
These are afferent to the capillary beds in villi. Once blood is oxygenated, it drains out of
the villi, into the umbilical vein. The oxygenated blood in the umbilical vein shunts past
the liver through the ductus venosus and drains to the inferior vena cava and the right
atrium. Because the foramen ovale and ductus arteriosus is open before birth, fetal blood
skips the pulmonary circulation and instead pours directly into the fetal systemic
circulation, thus carrying oxygenated blood to vital organs. Now imagine that you are an
oxygen molecule in the ivs. How did you get there from the maternal lungs? What
cellular and basement membrane barriers would you need to cross to get from the ivs into
a fetal RBC?
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MALE REPRODUCTIVE SYSTEM
Objectives
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•
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•
•
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Understand basic testicular microscopic anatomy. Learn to locate and recognize
different stages of spermatogenesis. Differentiate seminiferous tubules from
interstitial tissue.
Learn pathway for conveyance and modification of spermatozoa from
seminiferous tubules, through rete testis and efferent ductules, to epididymis.
Understand how ducts and accessory glands modify outflow from testes,
Be able to identify and distinguish between ductus epididymidis, ductus deferens,
seminal vesicles, and prostate glands
Locate periurethral and main glands in prostate gland.
Know basic morphology of penis.
Overview
The most important organs of the male reproductive system are the pair testes,
which are contained within the scrotum. The testes consist of seminiferous tubules, where
spermatogenesis occurs, and interstitial tissue, with testosterone-secreting Leydig cells.
During passage through a complex series of tubular ducts, the outflow of the testes is
modified mostly by absorption of fluids and partially by modification of spermatozoa to
make them more competent to fertilize ova. Glandular diverticula from this tubular
pathway contribute nutrients, enzymatically active constituents, and passive carrier
glycoproteins to make up an ejaculate containing about 200,000,000 gametes. The penis
introduces this semen into the female reproductive tract so that fertilization can occur.
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Slide 68, Testis, Ductus Epididymidis, Ductus Deferens,
H&E
This is a complex slide taken from near the mediastinum testis. On the bottom, there is a
large portion of a testis with seminiferous tubules (ST). Between the seminiferous
tubules, locate interstitial connective tissue and Leydig cells. Do not bother to try to study
the different constituents of the seminiferous epithelium in this slide. The fixation is poor.
Use the next slide for this job. The capsule of the testis is the tunica albuginea (TA). In
the hilum of the testis, you can find the rete testis (RT) and the efferent ductules (ED)
and above and to the right is a part of the ductus epididymidis (DE) and ductus
deferens (DD). How does a spermatozoon get from the seminiferous tubules to the
ductus deferens? Study and learn the characteristics of each of these passages. The ductus
epididymidis (aka epididymis) is a long (several meters), tortuously coiled tube that
conveys spermatozoa from the efferent ductules to the ductus deferens. It is lined by a
pseudostratified columnar epithelium composed mainly of two cell types, 1) short, fat
basal cells and 2) tall columnar principal cells with apical stereocilia (long microvilli).
Notice that the lumina of the epididymis are filled with spermatozoa. The tubules of the
epididymis are surrounded by uninnervated myoid cells in the head (near the efferent
ductules) but autonomically innervated smooth muscle cells in the tail (near the ductus
deferens). During ejaculation, smooth muscle contraction passes spermatozoa on to the
ductus deferens (aka vas deferens), which has an epithelium much like the epididymis
except that the principal cells are not as tall.
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Slide 31, Testis, H&E
This is a thin plastic section of a portion of a testis. The tunica albuginea (TA) and
seminiferous tubules (ST) are clearly marked. Find some good seminiferous tubules are
low magnification and then examine them at intermediate and high power. Use your atlas
and class notes to locate all of the following cells:
•
•
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Leydig cells,
Sertoli cells
Spermatogonia, primary and secondary spermatocytes (difficult to
distinguish), spermatids, and spermatozoa.
Slide 34, Efferent Ductules, H&E
The efferent ductules convey spermatozoa from the rete testis to the epididymis. There
are about 10-15 of these coiled tubules. Each is lined by a characteristic scalloped
epithelium composed of a clusters of tall ciliated columnar cells interspersed with
islands of short, nonciliated columnar cells. The cilia beat toward the epididymis. The
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chief function of the efferent ductules, aside from serving as a conduit for spermatozoa, is
resorption of fluid coming from the seminiferous tubules. A layer or two of myoid cells,
whose intrinsic contractile activities pass spermatozoa downstream toward the
epididymis, surrounds the efferent ductules.
Slide 67, Spermatic Cord, H&E
The spermatic cord contains a transverse section through the ductus deferens (DD) and
the cremaster muscle (CM) as well as numerous sections through the testicular artery
(afferent to testis) and pampiniform plexus of veins (efferent from testis). Study the
ductus deferens first. Notice that it is lined by a pseudostratified columnar epithelium
with principal cells (with stereocilia) and basal cells. There is a conspicuous, threelayered smooth muscular coat in the wall of the ductus deferens (outer and inner
longitudinal, middle circular). This smooth muscle contracts spasmodically during
ejaculation. Notice the nuclei of the spermatozoa in the lumen. The cremaster muscle is
skeletal muscle. It is unusual because it contracts involuntarily to lift the testes toward the
body cavity when an individual is cold or frightened and during ejaculation. The
pampiniform plexus surrounds the testicular artery and cools blood on the way to the
testes by radiation, ensuring the slight lowering of core body temperature required for
spermatogenesis. Varicosities in these veins (varicocele) can compromise their cooling
function, leading to an increase in testicular temperature and infertility. Surgical repair of
this anatomic defect can restore fertility.
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Slide 69, Seminal Vesicle, H&E
The seminal vesicles are paired diverticula of the ampullary portion of the ductus
deferens. Each seminal vesicle is basically a cul de sac with an elaborately folded
mucosa (M). In this thin plastic section, you will be able to find primary, secondary, and
tertiary mucosal folds. The mucosal epithelium is pseudostratified columnar epithelium.
The tall columnar cells secrete about 70% of the volume of the ejaculate. The tall
columnar secretory cells have apical cytoplasmic vacuoles filled with mucoid secretions,
which also spill over into the lumina. Notice that there are no spermatozoa in these
lumina. The short basal cells are most likely a stem cell population. A thick coat of
smooth muscle (SM) surrounds the organ.
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Slide 70, Prostate Gland, H&E
This is a thin plastic section taken from the edge of the prostate. There is an obvious
capsule (C) with numerous smooth muscle cells and a dense fibrous mat of CT. There
are also many main prostatic glands (MG), lined by a low pseudostratified columnar
epithelium with secretory and basal cells. Prostatic concretions (corpora amylacea) are
large, ovoid, eosinophilic, lamellated bodies filling many lumina. They are condensations
of prostatic secretions and dead cells.
Slide 76, Prostate Gland, H&E
This section is taken through the center of the prostate and includes a bowed section
through the prostatic urethra (U) and a small hillock called the verumontanum (V)
(aka seminal colliculus). The peripheral main prostatic glands (MG) have ducts that
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enter the prostatic urethra near the ejaculatory ducts (not included in this section). When
the epithelium of these glands undergoes malignant transformation, prostatic carcinoma
results. Adjacent to the prostatic urethra, especially anteriorly (to the right), you can see
mucosal and submucosal glands. Benign hyperplasia of these glands results in nodal
hyperplasia (benign prostatic hyperplasia).
Slide 71, Penis, Monkey, H&E
This slide is a cross section through the penis of a small nonhuman primate. The corpus
cavernosum urethrae (CCU) (aka corpus spongiosum) is a body of erectile tissue that
surrounds the penile urethra. Notice that the penile urethra is lined by an unusual
stratified columnar epithelium. Observe the paired corpora cavernosa penis (CCP)
(aka corpora cavernosa). A dense CT capsule called the tunica albuginea surrounds and
separates the corpora and attaches them to overlying skin (skin not in this slide). In the
middle of the corpora, there are numerous vascular spaces that become distended with
blood during erection of the penis.
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UPPER RESPIRATORY SYSTEM
Objectives
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•
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Study epithelium on nasal conchae (turbinates) and compare it to olfactory
epithelium.
Study microscopic anatomy of epiglottis and larynx.
Relate structure to function in these three organs
Overview
Much of the upper respiratory system is lined by a pseudostratified ciliated
columnar epithelium with goblet cells. The nasal conchae (turbinates) are complex
labyrinthine folds of the maxillary and ethmoid bones of the skull. Air entering the nasal
cavity is cleansed, warmed or cooled, and moistened as it passes over these surfaces. The
olfactory epithelium, a modification of the epithelium covering the rest of the conchae, is
responsible for our sense of smell. The epiglottis is a flexible flap of tissue that prevents
ingested liquids and solids from entering the respiratory system. We have a reflex that
presses the epiglottis over the opening of the larynx when we swallow and opens it when
we breathe and speak. The larynx is a complex cage of cartilage that sits atop the larynx.
It contains the vocal cords and allows us to make the complex sounds of speech.
Slide 39, Nasal Conchae, Nasal Septum, Olfactory
Epithelium, H&E
This section passes in the frontal plane of the face and includes the nasal septum (ns)
(hyaline cartilage), and several folded plates of bone, the nasal conchae (c). This is not a
human specimen. The conchae are more complex than those found in a human specimen.
You can find one of the two patches of olfactory epithelium (oe) in this slide. The nasal
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conchae are thin plates of bone embedded in a thin lamina propria with numerous blood
vessels and covered by pseudostratified ciliated columnar (PCC) epithelium with
goblet cells. The goblet cells produce a film of mucus that traps much particulate matter
in inspired air. This debris is then swept off the conchae by cilia. Inspired air flows into
the labyrinthine turbinates and the laminar flow immediately becomes turbulent. This
turbulence will project particulate matter into the conchae, where it will be trapped by the
mucus and removed by the cilia. The olfactory epithelium looks superficially like the
epithelium covering the conchae but closer examination reveals that it is much thicker
and lacks goblet cells. The olfactory cells here are highly modified ciliated cells. You
can also find supportive (sustentacular) cells and basal cells in the olfactory epithelium.
The mammalian olfactory epithelium turns over monthly as basal cells differentiate into
olfactory and sustentacular cells. The olfactory cells are bipolar neurons. Their cilia are
exceptionally long but nonmotile. Embedded in the ciliary membranes of the olfactory
cells are transmembrane proteins that act as chemoreceptors (chemically-gated ion
channels). Axons from these receptors are bundled into the fila olfactoria, which then
project through the cribriform plate of the ethmoid bone into the olfactory bulbs of the
brain. In essence, here one finds neurons that project directly into the CNS. This is the
most direct route of infection from the skin to the CNS. In the lamina propria of the
olfactory mucosa, Bowman glands secrete serous solvent/diluents for compounds that
we would smell.
Slide SL065, Epiglottis, Elastic Stain
In this specimen, with the epiglottis flopped down to cover the glottis, the left, proximal
(Prox) edge is attached to the tongue; the right, distal (Dis) edge is near the glottal
margin; the top is inferior; and the bottom is superior. The entire superior surface of the
epiglottis and the anterior part of the inferior surface is covered by a stratified squamous
unkeratinized epithelium (StSq). The posterior part of the inferior surface is covered by a
pseudostratified, ciliated, columnar epithelium with goblet cells (PCC), quite similar to
the mucosal lining of most of the larynx and the trachea. There are also mixed glands (G)
in the inferior lamina propria and a thick bar of elastic cartilage (EC) in the middle of the
epiglottis.
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Slide 36, Larynx, H&E
This is a section through part of the wall of the larynx. The section passes parallel to the
long axis of the laryngeal wall, through the thyroid cartilage (TC). The vocal fold (VF),
ventricle (V), and false vocal (ventricular) fold (FVF) are also indicated. On this slide,
start at the left (superior) part and move along the lumen of the larynx at intermediate
power. You may see PCC epithelium, then stratified squamous keratinized, and then
PCC again. Basically, in the larynx superior and inferior to the vocal folds, one finds
PCC epithelium, but over the surfaces of the vocal folds, which are frequently subjected
to abrasion, there is stratified squamous epithelium. There are also many large mixed
glands that empty into the ventricle to moisten and protect the vocal folds and numerous
lymphoid aggregates in the lamina propria. Skeletal muscle is common, representing
several different intrinsic laryngeal muscles, including the vocalis muscles in the vocal
fold.
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UPPER DIGESTIVE TRACT
Objectives
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•
•
•
•
Study microscopic anatomy of lip
Study microscopic anatomy of tongue and taste buds
Study a developing tooth
Learn to differentiate the three main salivary glands
Learn the microscopic anatomy of the oropharynx
Overview
The oral cavity contains structures for initial preparation of food. The lips and
tongue aid ingestion, the teeth break up food, and the salivary glands moisten it and begin
digestion. Then, small globs of food pass through the oropharynx into the esophagus on
their way to the stomach.
Slide 40, Upper Lip, H&E
The outer portion of the upper lip (UL) is on the bottom on this slide. The inner portion
is on the top. The vermilion border (V) is on the left. There is a small labial salivary
gland (G) in the top center. The acini here are mixed with mucous acini with serous
demilunes. The ducts of these glands are lined by stratified columnar epithelium. The
epithelium over the entire lip is stratified squamous keratinized, with hair follicles and
sebaceous glands and thicker stratum corneum on the outer surface and exceedingly thin
stratum corneum on the inner side. It is debatable whether the oral mucosa is
keratinized, but if so, it is only slightly keratinized. I was able to observe areas where
there were cells without nuclei apically in the stratum corneum, indicating that the oral
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mucosa is lightly keratinized. At the vermilion border, there are more blood vessels in
the dermis and they are superficial, imparting the red color to the lips of some people.
Skeletal muscle fibers of the orbicularis oris are also obvious.
Slide 41, Tongue, H&E
This is a section through the tip of the tongue. The upper surface (US) has many filiform
papillae and a few fungiform papillae. The epithelium here is stratified squamous and
lightly keratinized. Parts of the oral mucosa are lightly keratinized (gingival, hard palate,
tongue) because of abrasion during eating and talking and other parts are unkeratinized.
You can also see intrinsic skeletal muscle fibers criss-crossing in the body of the tongue.
Slide 42, Posterior Tongue with Circumvallate Papilla,
H&E
This thin plastic section is taken from the root of the tongue and contains a single
circumvallate papilla (CVP) at the bottom. There are many serous and mucous minor
salivary glands here and just below the CVP, there are small serous von Ebner glands.
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Examine the CVP at high magnification and find taste buds and their sensory nerves.
Most of what you see here is sections through criss-crossing skeletal muscle fibers of the
intrinsic muscles.
Slide 43, Developing Tooth, H&E
This slide contains a developing molar from a laboratory animal. The tooth rudiment is
embedded in a socket of bone (b). It has a pulp cavity (P) filled with embryonic
mesenchyme. The darkly stained M-shaped structure is the crown (C) of the tooth. Go to
high magnification and starting in the pulp cavity near the crown, slowly move toward
the crown. As you do so, find odontoblasts, predentin, dentin, dentinal tubules,
enamel, and ameloblasts. Dentin is very similar to bone. In dentin, the odontoblasts are
homologous to osteoblasts and osteocytes. What bone structure is homologous to the
dentinal tubules?
Overview of Salivary Gland Morphology
• Acini (alveoli) can be serous (parotid), mucous (sublingual), or mixed mucous
and mucous with serous demilunes (submandibular)
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•
•
•
Acini surrounded by myoepithelial cells
Glands are divided into lobules by CT septa
Ducts draining acini are either intralobular (intercalated- most distal, cuboidal
epithelium) and striated ducts- receives output from intercalated ducts (lined by
striated columnar epithelium) or interlobular (in CT, lined by stratified cuboidal
epithelium)
Salivation produces about 1 liter of fluid a day, parasympathetic innervation
increases volume of saliva, sympathetic (β-adrenergic) innervation increases
secretion of smaller volume of more viscous, protein-rich secretion.
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Slide 44, Parotid Salivary Gland, H&E
The salivary glands have lobules (L1 and L2) separated by CT septa. Within the lobules,
the parotid gland has all serous acini, long intercalated ducts, short striated ducts, and
numerous intralobular ducts. Look in the CT septa for larger (proximal) interlobular
ducts.
Slide 45, Submandibular Salivary Gland, H&E
The submandibular salivary gland contains many serous acini, and a few mucous acini
with serous demilunes. The striated ducts are quite well-developed in this specimen but
the intercalated ducts are short and inconspicuous.
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Slide 46, Sublingual Salivary Gland, H&E
This specimen of the sublingual salivary gland consists almost exclusively of mucous
acini. The myoepithelial cells are quite clear at the edges of acini. Both the intercalated
ducts and the striated ducts are poorly developed.
Slide 48, Oropharynx, H&E
The oropharynx looks superficially quite like the upper esophagus. Its luminal (L)
mucosa is covered by a stratified squamous unkeratinized epithelium (ssu). Unlike the
upper esophagus, however, it lacks a muscularis mucosae (instead having a layer of
elastic fibers) and therefore has no clear boundary between mucosa and submucosa. In
addition, the skeletal muscle fibers in the muscularis externa are arranged predominantly
as an inner longitudinal and an outer circular layer, the opposite of the esophagus.
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