INTRODUCTION TO DYNAMIC HISTOLOGY – ANAT 261
LABORATORY REVIEWS
WRITTEN BY: LAUREN KATZ
REVISED BY CARLOS R. MORALES
INDEX
Lab 1 (Skin and Epithelial tissue) …………………………………………………... Page 1
Lab 2 (Skin and Annexes).…………………………………………………………..
Page 4
Lab 3 (Cartilage and Bone).…………………………………………………………
Page 8
Lab 4 (Bone Formation) ……………………………………………………….........
Page 12
Lab 5 (Muscle Tissue) …………………………………………………………..…… Page 14
Lab 6 (Blood Vessels) …………………………………………………………..…… Page 18
Lab 7 (Respiratory System).…………………………………………………….……. Page 21
Lab 8 (Oral Cavity).………………………………………………………………..…. Page 25
Lab 9 (Digestive Tract).………………………………………………………………. Page 28
Lab 10 (Associated Glands).…………………………………………….………….... Page 33
Lab 11 (Urinary System) …………………………………………………….………. Page 38
Lab 12 (Nervous System) ……………………………………………………………. Page 43
Summary: Epithelial Tissue ..………………………………………………………… Page 46
Summary: Connective Tissue.…………………..……………………………...…….. Page 47
ANAT 261 — LAB REVIEW #1
SKIN & EPITHELIAL TISSUE
In this lab we will explore the structure of epithelial tissue of the skin. The skin is an
organ made up of epithelial tissue and connective tissue. Epithelial tissue forms sheets that cover
the outside of our bodies (skin) as well as line the respiratory tract, digestive tract, and capillaries
(for capillaries, the epithelium exists as a one layer of squamous cells called endothelium).
Epithelial tissue has some important characteristics:
a) Cells are tightly packed leaving little intercellular space
b) Has a basement membrane upon which the basal layer of cells rests
c) Cells are polarized, meaning they proliferate in a directional fashion
The classification of epithelia is based on:
a) The shape of cells (squamous [flat], cuboidal [square], columnar [rectangular])
b) The apical surface modification (cilia, microvilli)
c) The number of cellular layers arranged in the tissue (simple [1 layer] or stratified [2 or
more layers])
It is important to note that the stain used on all of the Light Microscopy (LM) slides is
Hematoxylin and Eosin (H&E). Hematoxylin, colours basophilic structures a purple-blue hue.
Basophilic structures usually contain nucleic acids such as DNA, RNA, ribosomes, and the
chromatin-rich nucleus. On the other hand, Eosin stains acidophilic structures a reddish-pink
colour. Examples include structures composed of proteins like collagen as well as the cytoplasm.
Hydrophobic structures such as fat cells and myelin around the axons of neurons do not stain
well with H&E. Note as well that the basement membrane present in all epithelial tissue does not
stain well with H&E. Instead, the PAS stain must be used.
SKIN —
Of the 4 main types of tissues in the body—Epithelial, Connective, Muscular, and Neural—the
skin is composed of 2: epithelial and connective tissue. The skin is divided into 3 main layers
called the epidermis, the dermis, and the hypodermis.
1. The epidermis is the outermost layer of the skin composed of epithelial tissue. More
specifically, the epithelium found here is classified as squamous stratified keratinized
epithelium. It is avascular (contains no blood vessels) and therefore receives nutrients
from the underlying connective tissue. The epithelium of the epidermis is composed of
different layers of cells as well as the basement membrane. From innermost to
outermost cells, the layers are:
i) Basement membrane (BM):
 This is not a layer of cells, but rather a layer of extracellular matrix (ECM) that lies
underneath the first layer of cells of ALL epithelium
 Composed of proteoglycans, glycoproteins, and collagens (including Collagen IV,
Laminin, Entactin, Nidogen, and Fibronectin
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ii)
iii)
iv)
v)
 It functions to attach the basal layer of epithelial cells to the connective tissue below
via the cellular junctions called hemidesmosomes
 This structure maintains the polarity and scaffolding of epithelial cells
 Serves as a filtration barrier allowing movement of nutrients and waste by diffusion,
and restriction the movement of harmful substances into the tissue
 As stated above, it is invisible in most LM slides except in the hair follicle and the
trachea
Stratum Germinativum (Stratum Basale):
 Composed of one layer of cells resting on the basement membrane
 These cells are columnar undifferentiated cells which give rise to all other cell
layers in the epithelium
 Some of these cells are stem cells which continuously undergo mitosis to replenish
the skin cells that are shed at the uppermost layer
 Note that this layer contains melanocytes which make melanin, the pigment that gives
skin its colour
Stratum Spinosum:
 Composed of a thick layer of polygonally-shaped differentiated cells connected via
cellular junctions called desmosomes, which allow the skin to have such great tensile
strength (resistance to tear with stress)
 These cells have centrally located nuclei and migrate from the stratum Germinativum
towards the upper layers of the epithelium
Stratum Granulosum:
 Composed of 1-2 layers of more squamous and elongated cells
 Cells contain non-membrane bound keratohyaline granules (basophilic) which
squish the nucleus as they increase in size in the cell
 The cells also contain lamellar bodies (membrane-bound structures filled with
phospholipids) which are released by exocytosis to form a lipid sheet covering the
stratum corneum
Stratum Corneum:
 Composed of dead cells which are keratinized
 Because the cells in this layer are dead, there are no nuclei or cell junctions
 Keratin is a fibrous structural protein (“a translucent scleroprotein”) that gives skin its
strength and waterproof property
 Note: with continuous pressure and rubbing on the skin, keratin proliferates forming
calluses
2. The dermis is the second layer of the skin and is composed of connective tissue (CT)
which provides support for the skin. It is separated from the epithelium via the
basement membrane and it separates the epidermis from the hypodermis. Unlike the
epidermis layer just above it, the dermis contains blood vessels and is therefore said to
be vascularized and innervated. CT is characterized by a large amount of
extracellular fibers (like collagen) and amorphous ground substance (called
extracellular matrix) which is composed of substances secreted by cells of the CT.
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There are two layers that compose the dermis:
i) Papillary layer:
 This is the upper layer of the dermis that stains a slightly lighter pink
 Composed of loose CT and contains many cellular elements
 Has a more disorganized appearance as compared to dense CT
 Loose CT is very cellular, flexible, vascularized, and not very resistant to stress
ii) Reticular layer:
 The lower layer of the dermis; stains a darker pink than the papillary layer
 Composed of dense CT and therefore has less cellular elements and more ECM
(collagen fibers and other fibrous elements)
 More specifically, the dense CT can be classified as irregular, meaning that the fibers
are not aligned in an orderly way as in dense regular CT (i.e. tendons)
 Dense CT offers resistance and protection and has less cells than loose CT
3. The hypodermis is the third and final layer of the skin. It connects the reticular layer
of the dermis to the underlying structures and organs. It is composed of loose CT with
a significant amount of adipocytes (fat cells). The adipocytes stain poorly with H&E
and therefore appear translucent under the microscope.
NOTE: Non-keratinized epithelium is characterized by the presence of nuclei in the top layers of
the cell. This is contrasted with keratinized epithelium where the top layer is composed of dead
cells lacking nuclei.
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ANAT 261 — LAB REVIEW #2
SKIN AND ANNEXES
This lab reviews the structure of the skin as well as other structures found in the different
layers of the skin: the hair, sebaceous gland, and sweat gland. For the structure of the skin, please
refer to the Lab 1 summary.
Glands are invaginations of secretory epithelium into the underlying connective tissue.
The type of glands discussed in this lab are called exocrine glands because their secretions are
secreted through a duct and have external destinations such as (i) the surface of the body or (ii) a
body cavity considered continuous with the external environment (i.e. the mouth). These glands
stand in contrast with endocrine glands which are ductless and secrete directly into the blood.
Before discussing the sweat and sebaceous glands, it is important to classify the different
types of exocrine glands according to their mechanisms of secretion. There are 3 types:
a) Merocrine gland (merocrine secretions)
 Only the secretion product is secreted—no part of the glandular cells is secreted; the
cells stay intact but all of their contents are emptied
 Examples: Exocrine pancreatic secretion
Secretions of the sweat gland
b) Apocrine gland (apocrine secretions)
 Part of the glandular cell is released with the secretion (the cytoplasm and part of the
plasma membrane), but the cell does not die
 Example: Mammary gland secretion (milk)
c) Holocrine gland (holocrine secretions)
 All of the cell’s contents are secreted (including the cytoplasm) and the cell dies
 Example: Sebaceous gland
SWEAT GLAND —
The sweat gland is a simple, coiled, tubular gland that opens at the surface of the skin. It serves
the purpose of thermoregulation of the body as the sweat evaporates from the surface of the
skin. This gland also regulates concentrations of water (secondary to the kidneys) and sodium.
The sweat gland is an example of a merocrine gland. These glands consist of a secretory portion
and an excretory portion:
1. The secretory portion:
 Located in the hypodermis immediately below the dermis
 This part of the gland is highly coiled in appearance
 The glandular cells are responsible for the collection of fluid and salt from surrounding
capillaries
 It consists of a single layer of columnar cells surrounded by myoepithelial cells (long and
flattened cells) which contract and squeeze the secretory part of the gland and push the
sweat out
 The secretion is composed mainly of water, urea, ammonia, and sodium chloride
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2. The excretory duct:
 Located in the dermis and leads all the way up through the epidermis to the surface of the
skin, releasing the sweat onto the skin’s surface
 2 layers of cuboidal cells with a central lumen where sweat flows outward
 This part of the gland serves to expel the sweat produced by the secretory portion
 There are no myoepithelial cells, and the cuboidal cells are more lightly colored than the
columnar cells of the secretory portion
SEBACEOUS GLAND —
The sebaceous gland is found at the upper part of the hair follicle in the dermis; in fact, the duct
of the sebaceous gland opens between the hair follicle to the hair shaft. In hairless areas of the
skin (called glabrous skin) the secretions of this gland are released directly onto the surface of
the skin. The sebaceous gland is a holocrine gland as the glandular cells die upon release of their
contents. The secretion of the sebaceous gland is called sebum and is thought to have some mild
anti-bacterial and anti-fungal properties. Sebum is composed of lipids and cell material (from the
holocrine secretion).
The following is a histological description of the gland as well as the process of secretion:
 The gland is made up of several layers of polygonal epithelial cells surrounded by CT
 The gland is formed by a bulb-like grouping of cells which migrate toward a single short
excretion duct
 As the cells mature, they accumulate lipids (cholesterol, glycogen, phospholipids,
triglycerides) giving the cells a ‘bubbly’ appearance
 While accumulating these lipids, they migrate towards the duct at the top of gland and begin
to die
 Note the disappearance of nuclei as the lipids accumulate and cells prepare to burst
 Eventually the cells burst and their contents as well as pieces of the cell are released
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HAIR —
The hair projects from the dermis, but arises from hair follicles located deep in the dermis layer
of the skin, bordering the hypodermis. The hair and the sebaceous gland together are known as
the pilosebaceous unit. The hair has several functions including thermoregulation, sensory
functions, and protection. The hair can be separated into 3 parts:
1. The hair bulb:
 This is the base of the hair located deep in the dermis
 The bulb contains stem cells, and as such is the region responsible for hair growth
 An important feature to note in this region is the dermal papilla—the invagination of the
papillary layer of the dermis between the two projections at the base of the hair (when
viewed in longitudinal section)
 The dermal papilla is essential for hair growth and maintenance
 It is vascularized and innervated and is therefore responsible for supplying blood to the
bulb as well as sending pain signals when the hair is pulled
 If the dermal papilla is destroyed—by pulling out the hair or damaging the skin to the level
of the dermal papilla—the hair will no longer grow at that site
2. The hair follicle:
 The part of the hair called the follicle spans the region from just below the arrector pili
muscle to just below the sebaceous gland
 The arrector pili is smooth muscle responsible for stiffening of the hair (goose bumps)
 In this part of the hair, cells have differentiated to form different distinct layers (moving
inwards):
i) Connective tissue sheath:
 A layer of CT from the dermis surrounding the follicle and bulb
ii) Glassy membrane:
 This is the basement membrane of the hair and can be seen under light
microscope
 This basement membrane is continuous with the basement membrane of the
epidermis (due to the invagination of the epidermis)
iii) External root sheath (ERS):
 Several layers of epithelial cells and is continuous with the epidermis
 This layer spans the region from the dermal papilla to the epidermis
iv) Internal root sheath (IRS):
 Spans the region from the hair bulb to the sebaceous gland
 Consists of 3 layers:
a) Henle’s layer – a single layer of cells without visible nuclei; does not
stain well so remains pale in the slide
b) Huxley’s layer – 2 identical layers of wider cells with visible nuclei;
composed of tricohyaline granules which are heavily stained by Eosin
c) Cuticle of the IRS – 1 layer of lighter flat cells; have the appearance of
shingles
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v) Cuticle of hair shaft:
a) Consists of 1 layer of cuboidal cells which flatten as they move towards
the end of the hair
b) Also has the appearance of shingles but stains darker than the cuticle of
the IRS
vi) Cortex:
 Located in the center of the hair, this part surrounds the medulla (if a medulla is
present) and comprises the widest portion of the hair shaft
vii) Medulla:
 The medulla will not be seen in the slide as it is only present in thick hairs of
humans and some animals
3. The hair shaft:
 This is the region above the end of the follicle (from just below the sebaceous gland) that
is exposed to the outside environment
 It is composed of:
i) Cuticle of the hair shaft
ii) Cortex
iii) Medulla (when present)
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ANAT 261 — LAB REVIEW #3
CARTILAGE AND BONE
In this lab, 2 types of supporting connective tissue will be examined: cartilage and bone.
In addition, tendon will be studied as an example of Dense Regular CT. First, we will briefly
review some important characteristics of CT.
In the body, CT functions to provide structural support to the surrounding tissues.
Unlike epithelial tissue which is composed mostly of cells, connective tissue is made up mostly
of extracellular matrix (ECM) consisting of protein fibers and ground substance. CT can be
classified according to the following diagram:
Different types of CT serve different functions; as supporting CT, bone and cartilage are
specialized forms of CT whose cells produce an ECM with a firm consistency. The ECM is
secreted by the cells of the particular tissue and ultimately this ECM envelopes and traps the
cells. The cells that are secreting the ECM have the suffix ‘____blast’ while the trapped cells
carry the suffix ‘____cyte’. For example, in cartilage, chondroblasts secrete ECM and at the
point when they are imprisoned with this ECM, they are referred to as chondrocytes.
CT consists of the cells of that particular type of CT, fibers, and ground substance (with
the latter two making up the ECM). It is the different concentrations of each of these
components, as well as the type of fiber present (collagen, reticular, or elastic) that will give the
CT its properties.
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—
Tendon is a good example of Dense Regular CT. In the body, tendons connect muscle to bone
and in doing so, allow the coupling of muscle contraction to movement of the bones. In this
tissue, you will notice the organized parallel arrangements of Collagen fibers as well as a small
population of fibrocytes that are sandwiched between these densely packed fibers.
DENSE REGULAR CT
CARTILAGE —
Cartilage allows tissue to support mechanical stress without distortion and provide support to
adjacent soft tissues. It consists of cells called chondrocytes and chondroblasts (immature
chondrocytes) as well as a network of ECM secreted by these cells. The cells reside in pockets
called lacunae within the ECM. Note that cartilage is avascular (has no blood vessels) because
nutrients can diffuse through the matrix from the perichondrium to the chondrocytes and wastes
can diffuse in the opposite direction.
The ECM of cartilage consists of:
a) Fibers – Collagen Type II (hyaline cartilage) or elastic fibers (elastic cartilage)
b) Ground substance – Proteoglycans (Keratan SO4, Chondroitin SO4, Hyaluronic acid) and
glycoproteins (Chondronectin)
 The GAGs of the proteoglycans are negatively charged and therefore attract water into
the ECM, giving cartilage its strength and resilience
Of the 3 types of cartilage—Hyaline, Elastic, and Fibrous—only the first two will be seen in the
lab:
1. Hyaline cartilage is the most common type of cartilage found in the body. It is found
on the surfaces of moveable joints, the epiphyseal plate, larynx, and trachea. It consists
of several layers and components:
i) Perichondrium: a layer of dense irregular CT that forms a type of protective capsule
around the cartilage except at joints
 The perichondrium consists of 2 layers: the upper Fibrous Layer composed of
fibrocytes and Collagen Type II, and the lower Chondrogenic Layer (or Cellular
Layer) which is composed of chondroblasts
 VERY IMPORTANT: the hyaline cartilage found in joints does not have a
perichondrium; this cartilage is called articular cartilage. It is surrounded by
synovial or articular fluid which provides cushion and nutrients to joint cartilage.
Since the perichondrium is responsible for cartilage repair, in the event of cartilage
damage on articular surfaces, it is repaired much more slowly (if at all) and depends
on growth of chondrocytes in the ECM.
ii) ECM with chondrocytes:
 As chondroblasts of the chondrogenic layer secrete ECM and mature, they become
more round in shape
 Eventually, they become trapped in the ECM in lacunae and at this point are referred
to as chondrocytes
 Groups of cells in a single lacuna that originate from 1 chondrocyte are called
isogenous groups; there can be up to 8 cells in one lacuna
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 A note about cartilage growth: appositional growth occurs in the chondrogenic layer of the
perichondrium where the chondroblasts differentiate and secrete ECM; interstitial growth
occurs by mitotic division of chondrocytes lower in the ECM. In articular cartilage, only
interstitial growth can occur because there is no perichondrium.
2. Elastic cartilage is very similar to hyaline cartilage, with the only distinguishable
difference being the presence of elastic fibers in the ECM. These fibers give this
cartilage its tremendous flexibility. Aside from these fibers, elastic cartilage is structural
similar as hyaline cartilage. It differs in use, as it is needed where highly
flexible support is required in the body like the epiglottis and the external ear.
BONE —
Bone serves to support body tissues, protect internal organs, facilitate movement, and is also
involved in regulation of blood Ca2+. It consists of 3 types of cells—osteoblasts, osteocytes, and
osteoclasts—as well as an ECM made of calcified materials and Collagen Type I.
The ECM of bone consists of:
a) Fibers – Collagen Type I
b) Calcified ground substance – Proteoglycans and glycoproteins
c) Minerals – Hydroxyapatite crystals
(Organic)
(Organic)
(Inorganic)
As mentioned previously, there are 3 types of cells present in bone:
i) Osteoblasts:
 Located in the periosteum, endosteum and in some Haversian systems, these cells
synthesize and secrete the organic components of bone: Collagen Type I in the
endosteum and in the zone of mixed spicules, and ground substance
 They are derived from osteoprogenitor cells (stem cells for bone)
 As they secrete ECM, they become trapped by the matrix
 Osteoblasts become osteocytes in the Outer Circumferential System, Inner
Circumferential System, Haversian Systems, etc.
ii) Osteocytes:
 These cells are flatter than osteoblasts and are found in lacunae
 Nutrients are provided to the cells and wastes are removed by tiny channels
emanating from the lacunae called canaliculi, which ultimately communicate with
the blood vessels in the Haversian canal
 These canaliculi are needed because the mineralized matrix of bone prevents
diffusion of nutrients through the matrix to the osteocytes
 Osteoprogenitor cells  Osteoblasts  Osteocytes
iii) Osteoclasts:
 These are large and multi-nucleated cells involved in bone resorption and
remodeling by degrading collagen and calcium, thereby affecting the concentration
of calcium in the blood
 These cells play a role in osteoporosis, a condition in which the bone mineral
density becomes too low
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There are 2 types of bone:
a) Spongy / cancellous bone:
 It appears as a discontinuous, disorganized arrangement of bone
 It is found in the epiphyses (ends) of long bones
b) Compact bone:
 It appears as a dense mass of bone with concentric rings containing centrally located
channels
 Found in the diaphysis (shaft) of long bones
Lamellar bone—meaning “layered bone”—is found in compact bone and has several layers and
structures that can be identified under the microscope (from outer layer to inner layer):
i) Periosteum:
 Forms a capsule of dense irregular CT around the circumference of bone
 Similar to the perichondrium in hyaline cartilage, this layer has a fibrous sublayer
composed of collagen and fibroblasts as well as an innermost cellular sublayer
composed of osteoprogenitor cells
ii) Outer Circumferential System (OCS):
 Consists of several layers of osteocytes just below the periosteum
 Encircles the circumference of the bone
iii) Haversian canal:
 Contains blood vessels, nerves, and loose CT
 The larger the Haversian canal, the younger the Haversian system
iv) Volkmann’s canal:
 These are canals that run perpendicular to Haversian canals and connect neighboring
osteons allowing “communication” between them
v) Haversian system or Osteon:
 This is the entire system of concentric layers of bone surrounding the Haversian canal
 Osteons are separated from each other by cementing lines which lie on the outermost
periphery of the osteon
vi) Interstitial system:
 This is suspected to be the remnants of a degrading Haversian system (function
unknown)
vii) Inner Circumferential System (ICS):
 It consists of layers of osteocytes that run parallel to the endosteum
viii) Endosteum:
 A single squamous layer of cells closest to the bone marrow
 Mainly composed of osteoprogenitor cells and osteoblasts
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ANAT 261 — LAB REVIEW #4
BONE FORMATION
This lab describes and discusses the types of bone formation (called ossification) as well
as the function and structure of the epiphyseal plate.
OSSIFICATION —
There are 2 types of bone formation:
1. Intramembranous ossification (not shown in the lab):
 Occurs in the mesenchyme of flat bones (i.e. skull, jaw), as well as long bones
 This ossification leads to appositional growth in the long bones (increase in diameter)
 The cells responsible for initiating this process are the mesenchymal cells, which are
multipotent stem cells residing in embryonic CT called the mesenchyme (these are
cells that can differentiate into many different types of cell of a particular function)
 First a group of these cells differentiate into osteoblasts to form the primary
ossification center
 The osteoblasts then produce bone ECM which is then calcified to form spicules; they
are then trapped by this matrix thereby becoming osteocytes
 Ossification centers expand outwards and fuse, resulting in the formation of spongy
bone
 An example is the soft spot on the head of a baby which is an area of CT that has not
yet been ossified
 Peripheral mesenchymal cells give rise to periosteum
2. Endochondral ossification:
 Endochondral, meaning ‘from within cartilage’, signifies ossification involving bone
formation from within an area of hyaline cartilage in the shape of the bone to be
formed
 This type of ossification allows for the formation of short and long bones
 The primary ossification center forms in the diaphysis where the perichondrium is
transformed into periosteum via intramembranous ossification, creating a bone collar
 Because the bone collar deprives the cartilage of nutrients, the chondrocytes die, the
cartilage degenerates, and the ECM is calcified
 Blood vessels invade the bone collar bringing osteoprogenitor cells
 Osteoblasts then stick to the calcified matrix and secrete bone ECM surrounding the
cartilage remnants
 The secondary ossification center is formed by the same mechanism but is situated in
the epiphyses of long bones
 Not all of the cartilage of the secondary ossification centers is turned into bone: some
remains on articular surfaces (joints) throughout life as well as in the epiphyseal plate
until around 20 years of age
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EPIPHYSEAL PLATE —
The epiphyseal plate connects the two epiphyses to the diaphysis and is responsible for growth
in length of long bones. At the end of the plate close to the epiphysis, the chondrocytes
proliferate while at the end close to the diaphysis, the chondrocytes hypertrophy, die, and deposit
a calcified matrix. Primary bone is then deposited on the calcified cartilage matrix by osteoblasts.
Until the age of 20, the thickness of the epiphyseal plate remains constant due to equal rates of
chondrocyte proliferation and cartilage matrix destruction.
There are 5 zones in the epiphyseal plate:
i) Zone of resting cartilage:
 Hyaline cartilage with normal cartilage cells
ii) Zone of proliferation:
 Chondrocytes are dividing rapidly by mitosis forming “stacks of coins”
 These cells are very acidophilic
iii) Zone of hypertrophy:
 Cells begin to enlarge and lacunae fill with glycogen, giving them a whiter appearance
iv) Zone of cell death:
 Disappearance of nuclei as cells begin to rupture and secrete calcified matrix
v) Zone of mixed spicules:
 Bone matrix (stained darker) is laid down over the calcified cartilage matrix (stained
lighter) by osteoblasts
 Osteoblasts, osteocytes, and osteoclasts are found in this zone
 The term “mixed spicules” indicates that the bone spicules in this area are composed of
both calcified cartilage matrix and bone
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ANAT 261 — LAB REVIEW #5
MUSCLE TISSUE
In this lab, we will study the histological differences between the 3 kinds of muscle found
in the body: smooth muscle, skeletal muscle, and cardiac muscle. Each type of muscle has
identifying characteristics that will allow you to differentiate one from the other. It is important
to be comfortable identifying muscle in both cross section and longitudinal section as both can
be tested on the lab exam.
Muscle is a complex tissue with many levels of organization:
Muscle
↓
Bundle of fibers (fascicle)
↓
Muscle fiber (muscle cell)
↓
Myofibril
↓
Myofilament (actin, myosin, etc.)
The myofilaments in skeletal and cardiac muscle are organized into contractile units
called sarcomeres. These are the smallest functional unit of contraction and are responsible for
the contraction of the entire muscle. The sarcomere has a distinct pattern of bands and lines
which indicate the organization of the myofilaments. This pattern can be seen when the muscle
cell is sectioned longitudinally:
Z line: the border of the sarcomere that bisects the I band; composed of α-actinin
I band: composed only of actin filaments (also called thin filaments)
A band: the largest band; composed of overlapping actin and myosin
H band: also called pseudo band H, is in the center region of the A band; composed only of
myosin (‘thick filaments’)
M line: dead center of the H band; composed of myosin with lateral connections between the
filaments, with creatine kinase as the major protein of this line
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Upon contraction, the actin and myosin fibers overlap (but do not shorten) resulting in a
shortening of the I band and H band. This is called the Sliding Filament Model of muscle
contraction.
Muscle tissue has some variations of the typical names given to certain cellular
structures. These variations include:
Sarcolemma: muscle cell plasma membrane
Sarcoplasm: muscle cell cytoplasm
Sarcoplasmic reticulum: muscle cell endoplasmic reticulum
Note that all types of muscle have the myofilaments actin and myosin; however, in
smooth muscle these filaments are not organized into sarcomeres. In addition, the structure of
myosin in smooth muscle is different from that in skeletal and cardiac. This difference in
structure renders myosin the limiting factor in smooth muscle contraction, while actin is the
limiting factor for the contraction of skeletal and cardiac muscle.
In skeletal muscle, a network of T-tubules and terminal cisternae (sarcoplasmic
reticulum) play an important role in the mechanism of muscle contraction. The T-tubules are
invaginations of the sarcolemma that allow for depolarization of the entire muscle fiber, not
simply the peripheral parts of the fiber. The term triad is used to describe a T-tubule sandwiched
between two terminal cisternae. The sarcoplasmic reticulum that surrounds the muscle fiber
stores Ca2+ and releases it upon depolarization of the muscle cell.
SMOOTH MUSCLE —
This type of muscle is responsible for slow, involuntary contractions. Examples of locations of
smooth muscle include the uterine wall, the tunica muscularis of the GI tract, the media layer of
major blood vessels, and the upper parts of the respiratory tract. The following is an outline of
the histological characteristics of smooth muscle:
a) Longitudinal section:
 No striations since myofibrils are not organized into sarcomeres
 Cytoplasm is homogenous and clear in appearance
 The cell shape is fusiform (wider middle and tapered ends)
 There is only one centrally located nucleus per cell
b) Cross section:
 Again, clear appearance of cytoplasm due to lack of sarcomere organization of
myofibrils
 Single centrally located nuclei
 As compared with cardiac muscle, there are no white ‘halos’ around the nucleus
- 15 -
SKELETAL MUSCLE —
This type of muscle is involved in quick and forceful voluntary contraction. Skeletal muscle
can be found associated with bones, in the tongue, the upper third of the esophagus, and in outer
anal sphincter to name a few.
Muscle cells, bundles of muscle cells, as well as groups of these bundles are separated by
connective tissue. The role of this CT is to:
i) Connect muscle fibers to each other
ii) Provide nutrients and blood
iii) Supply nerves
iv) Attach muscle to bone through tendons (dense regular CT) to transduce muscle
contraction into movement
The CT surrounding the entire muscle is called the epimysium, followed by the perimysium
which separates bundles of muscle cells (fascicles). Finally, the endomysium surrounds
individual muscle cells and is comprised of the basement membrane of the muscle cell and
reticular fibers.
This type of muscle has a very distinct histological appearance and is quite easy to
differentiate from both smooth and cardiac muscle:
a) Longitudinal section:
 Very prominent striations due to sarcomere organization
 Many flattened, elongated nuclei line the periphery of the cell
 Cells are very long
b) Cross section:
 Due to the myofilaments, the cytoplasm appears grainy
 Nuclei appear round and small and are located at the periphery of the cell
**Nuclei of muscle cells are located under the sarcolemma while fibrocyte nuclei (of the
surrounding CT) are located on the outside of the muscle cell plasma membrane—make sure you
don’t confuse the peripheral nuclei of skeletal muscle with the fibrocytes of the CT surrounding
the muscle fibers. You can differentiate the fibrocytes from the nuclei by a difference in color
(fibrocytes are darker and more dense) and shape (fibrocytes are more elongated and muscle
nuclei are more rounded).
CARDIAC MUSCLE —
This type of muscle allows for involuntary, vigorous, rhythmic contractions. Cardiac muscle is
only found in one place in the body: the heart. Similar to skeletal muscle, cardiac muscle is
organized into sarcomeres and is surrounded by a layer of CT, but only to the level of the
perimysium. Cardiac muscle has different characteristics that serve as identifiers in longitudinal
and cross section:
- 16 -
a) Longitudinal section:
 Striations can be seen due to the presence of sarcomeres
 These cells are branched and have only one nucleus per cell
 This is the only type of muscle that has intercalated disks which will appear at a
perpendicular angle to the length of the cell
 These intercalated disks allow for the synchronization of muscle contraction via gap
junctions which permit rapid conduction of electrical signals from cell to cell
 Nuclei are centrally located, similar to smooth muscle but unlike skeletal muscle
b) Cross section:
 Centrally located nuclei are an important feature in distinguishing this cell from
skeletal muscle (which has peripherally located nuclei)
 Note that smooth muscle also has centrally located nuclei, so the presence of a grainy
cytoplasm would allow the identification of the tissue as cardiac muscle
 A while halo can be seen around the nucleus; this halo contains glycogen and does not
stain well with H&E therefore it remains white
- 17 -
ANAT 261 — LAB REVIEW #6
BLOOD VESSELS
In this lab we will be differentiating between the different types of blood vessels that
appear in the body. Sometimes a given vessel might be difficult to classify because in reality, the
changes in blood vessels in the body are gradual and therefore so are the changes in histological
characteristics. However, on the lab exam there will be no ambiguity as very definite structures
will be given. In addition, you are responsible for the theory concerning Medium Sized Veins but
they will be not tested on the lab exam nor do they appear in the lab.
The arterial vessels of the circulatory system are termed the efferent vessels as they
transport blood away from the heart, and conversely the venous vessels are termed afferent
vessels as they bring blood back to the heart.
The walls of blood vessels consist of 3 types of tissue—epithelial tissue, connective
tissue, and muscular tissue. These tissues are organized into distinct layers:
1. Initima (inner layer; closest to lumen):
 First is the endothelial layer composed of simple squamous epithelium
 Endothelium is a semi-permeable barrier between the blood and the ISF (interstitial
fluid) allowing gas and nutrient exchange
 In arteries, the sub-endothelial layer (CT remnant) lies below the basement
membrane of the endothelium
 In some vessels, there is an Internal Elastic Limiting Membrane (IELM) under the
sub-endothelial layer which appears very wavy in cross section
2. Media (middle layer):
 Composed of smooth muscle (number of layers depends on the vessel)
 In Elastic Arteries there are layers of elastic membrane made of elastin
 Reticular fibers (Collagen Type III), proteoglycans, and glycoproteins are present
among smooth muscle (lends strength and resistance to the vessel)
3. Adventitia (outer layer):
 Composed of dense irregular CT
 Network of small vessels called vasa vasorum, meaning ‘vessel of a vessel
 Allows diffusion of nutrients into the adventitia
 Vasa vasorum are found in large vessels
 This layer has Collagen Type I
Lymphatic vessels will not be seen in the lab, but they are an important component of the
circulatory system. They return excess fluid from the tissues to the circulation.
The characteristics of the media will allow you to distinguish between arteries:
 Elastic arteries have many layers of smooth muscle with elastic fiber lamellae
 Muscular arteries have 4 or more layers of smooth muscle and completely lack a layered
system of elastic fibers
 Arterioles have 1 to 2 layers of smooth muscle and lack elastic fibers
- 18 -
SUMMARY OF THE CHARACTERISTICS OF BLOOD VESSELS —
INTIMA
MEDIA
ADVENTIA
 Dense irregular CT
(fibrocytes, collagen
fibers, elastic fibers)
 Vasa vasorum (small
vessels)
 Dense CT
 Vasa vasorum in
larger vessels
Elastic artery
Ex: Aorta,
large branches
of Aorta
 Endothelium
 Sub-endothelium
 IELM (1st layer of
elastic fibers)
 Very thick layer
 Many elastic fibers
 Smooth muscle layers
alternate with elastic fibers
 Smooth muscle cells run in
many different directions
Muscular
artery
 Endothelium
 Sub-endothelium
 IELM prominent
 Thick layer
 4 or more layers of smooth
muscle
 No elastic fibers
Arteriole
 Endothelium
 Thin sub-endothelium
 No IELM
 1-2 layers of smooth
 Instead there is an
muscle
Internal Elastica
(elastic fibers—not a
membrane)
 Very thin layer of
dense CT
Capillary
 Endothelium only
 No sub-endothelium
 No IELM
 Absent
 Basement membrane
and reticular fibers
surround endothelium
Venule
 Endothelium only
 No sub-endothelium
 No IELM
 Smooth muscle is absent
 Location of pericytes (not
seen in lab)
 Basement membrane
 Very thin layer of CT
 Endothelium
Large vein
Ex: Vena Cava,  No sub-endothelium
Carotid Vein
 No IELM
 Incomplete layers of
smooth muscle
 Thin relative to adventitia
 Thick longitudinal
smooth muscle
 Dense irregular CT
 Vasa vasorum
NOTE: Do not confuse capillaries with venules. Although they share some of the same
characteristics, keep in mind that capillaries are much smaller than venules—a single erythrocyte
(RBC) fills almost the entire diameter of a capillary, but not that of a venule.
- 19 -
A COMPARISON OF AN ARTERY AND VEIN OF THE SAME SIZE —
ARTERY
VEIN
 Smaller lumen
 Larger lumen
 More elastic and muscular tissue
 Thicker, more rigid walls due to stronger
blood pressure in these vessels
 Less likely to collapse when sectioned
 More collagenous tissue; more loosely
constructed
 Less elastic and muscular tissue
 Thinner walls due to decreased blood
pressure in these vessels
 Collapse readily when sectioned
 More pronounced media
 More pronounced adventitia
 No valves
 Valves present
Finally, when viewing the different sections, keep in mind that endothelial cells run
parallel to the vessel while the smooth muscle runs perpendicular to the vessel. As a result, when
the vessel is cut longitudinally the endothelial cells appear in longitudinal section while the
smooth muscle cells appear in cross section. On the other hand, when the vessel is cut in cross
section the endothelial cells appear in cross section while the smooth muscle cells appear in
longitudinal section. The organization of smooth muscle in this way permits constriction of the
vessel upon contraction of the muscle cells, and dilation of the vessel upon relaxation of the
muscle cells.
- 20 -
ANAT 261 — LAB REVIEW #7
RESPIRATORY SYSTEM
The function of the respiratory system is to provide oxygen and remove carbon
dioxide from the blood to maintain the tissues of the body—a mechanism called gas exchange.
The respiratory system consists of 3 zones, each having a distinct function:
i) Conducting zone:
 Consists of the nasal cavity, larynx, trachea, bronchi, regular bronchioles, and
terminal bronchioles
 Cartilage and smooth muscle are present to varying degrees (depending on the
structure), serving to keep the airways open
 This zone is responsible for allowing air to pass into the deeper part of the respiratory
system (the respiratory zone) where gas exchange takes place
 Serves to clean, warm, and moisten air before it reaches the alveoli (called
‘conditioning the air’)
 There is no gas exchange in this zone
ii) Transitional zone:
 Consists of the respiratory bronchioles
 This zone is a transitional segment between the conducting zone and the respiratory
zone
 Smooth muscle is still present, but there is no cartilage
 The function of this zone is to keep the airways open as well as warm and moisten the
air before it reaches the alveoli
 The beginning of gas exchange takes place in this zone
iii) Respiratory zone:
 Consists of the alveolar ducts, alveolar sacs, and lung alveoli
 There is no cartilage and almost no smooth muscle in this zone
 This area is responsible for gas exchange
Similar to the blood vessels, the conducting zone of the respiratory tract follows a general
plan that spans the entire zone. The layers of the conducting portion are as follows (from
innermost to outermost):
1. Mucosa (closest to the lumen):
 The innermost layer is composed of respiratory epithelium which is classified as
ciliated pseudostratified columnar epithelium with goblet cells
 This respiratory epithelium spans the region from the nasal cavity to the bronchi—
note that there are no goblet cells in the bronchioles
 Under the basement membrane of the epithelium lies the lamina propria, which is
composed of loose CT, elastic fibers, and capillaries (analogous to the papillary layer
of the dermis)
- 21 -
2. Sub-mucosa:
 This layer lies underneath the mucosa and is comprised of fibrous dense irregular CT
of varying thickness
 The acinar glands (serous and mucous) present in this layer have ducts that open into
the lumen of the respiratory tract
 Note that in the nasal cavity only, the glands are in the lamina propria
 Varying quantities of cartilage and muscle are found in the submucosa
 C-shaped hyaline cartilage rings are present in the trachea and the bronchi to a lesser
extent (discontinuous cartilage)
 Note that these cartilage rings are surrounded by a perichondrium
 The trachealis muscle (smooth muscle) is present at the back of the trachea and serves
to bridge the gap between the ends of the cartilage rings
 A smooth muscle layer is present in post-tracheal structures of the conducting zone
 The cartilage and muscle are needed to provide support and keep the airway open
3. Adventitia (furthest from the lumen):
 This layer below the cartilage and muscle is composed of dense irregular CT
 The function of this layer is to attach the structure (i.e. trachea, bronchus) to other
organs or tissues in the body
Because respiratory epithelium is so important, it is necessary to be familiar with the
different types of cells comprising the tissue, as well as the functions of these cells:
i) Ciliated cell: these cells are the tallest in this epithelium and have tiny hair-like
projections called cilia on the apical border (recall: 9 + 2 configuration)
ii) Brush cell: these cells have microvilli which create a brush border on the cell; note that
microvilli are not like cilia, but rather they are projections of the plasma membrane that
serve to increase the surface area of the apical surface
iii) Small granule cell (Argentaffin cell): these cells secrete epinephrine and serotonin facing
the basement membrane (not into the lumen)
iv) Short cell: these are the stem cells of this epithelium therefore they are undergoing
continuous mitosis; these cells are the precursors of the brush cells which then differentiate
into ciliated cells. They are also the precursors of goblet cells and small granule cells
v) Goblet cell: these cells are filled with glycoproteins that are secreted by exocytosis
- 22 -
SUMMARY OF THE CHARACTERISTICS OF THE RESPIRATORY TRACT —
MUCOSA
Trachea
 Respiratory epithelium and
basement membrane of
epithelium
 Lamina propria
Intrapulmonary
Bronchus
Regular
bronchiole
Terminal
bronchiole
 Wavy respiratory epithelium
(cross sect.) with fewer goblet
cells than in trachea
 Highly vascular lamina propria
(many vessels)
 Simple ciliated columnar
epithelium without goblet cells
 Wavy epithelium due to
contraction of smooth muscle
cells
 Thin lamina propria
 Continuous transitional layer:
simple ciliated columnar cells
and non-ciliated cuboidal
Clara cells (stain lighter than
ciliated cells)
 Less wavy due to less smooth
muscle cells
 Lamina propria almost absent
SUBMUCOSA
ADVENTITIA
 Dense irregular CT
 Acinar glands (serous, mucous and
seromucous acini)
 Dense
 Thick C-shaped hyaline cartilage
irregular CT
rings
 Trachealis muscle and other
smooth muscle around cartilage
 Dense irregular CT
 Only serous acini (mucous acini
 Thin layer of
would occlude the lumen with
dense irregular
mucous)
CT mixed
 Hyaline cartilage present in plates,
with lung
not continuous rings
tissue
 Smooth muscle above cartilage
 Abundance of smooth muscle
(organized into 2 spiraling layers)
 No cartilage
 No glands
 Few smooth muscle cells
 Wall remains intact and
continuous
 No cartilage
 No glands
 Smooth muscle cells touch the
Respiratory
epithelium due to lack of lamina
bronchiole  Discontinuous shorter cuboidal
(transitional
epithelium with neither goblet
propria
region)
cells nor ciliated cells
 Smooth muscle cells are
 Clara cells are present
discontinuous and form large
 No lamina propria
projections
 Wall is discontinuous
 May have patches of alveolar
tissue
Alveolar
duct
 Mucosa exists as knob-like
projections
 No lamina propria
 Discontinuous Clara cell layer
 Discontinuous smooth muscle
within the epithelial knobs
 No glands
- 23 -
 Unclear layer
(very thin,
mixed with
lung tissue)
 Unclear layer
 Unclear layer
 Unclear layer
The alveolar sac follows the alveolar duct, and the respiratory zone finally ends in the
alveoli of the lung. Notice that there are no more knobs of smooth muscle in the alveolar sac or
the alveoli but small amounts of smooth muscle remain in the alveolar ducts. The alveoli are the
main site of gas exchange in the lungs. The air traces a pathway from the conducting zone of the
respiratory tract, through the transitional zone, and finally reaches the respiratory zone where the
gases diffuse down their concentration gradients and are exchange across the alveolar and
capillary walls. There are 4 types of cells located in the lung alveoli:
i) Type I pneumocyte:
 Simple squamous epithelial cell lining the alveolar lumen
 Rests on a basement membrane which is shares with the capillary endothelial cell
ii) Type II pneumocyte:
 This secretory epithelial cell is often wedged near the corners of the interalveolar
septum (the elastic fiber wall separating the alveoli)
 Has a prominent round nucleus and lamellar bodies within the cytoplasm
 This cell has a very special purpose: it secretes pulmonary surfactant which covers
the Type I pneumocytes (i.e. covers the entire alveolar surface)
 This surfactant serves to lower the surface tension of the alveoli, which allows them to
inflate readily upon inspiration so gas exchange can occur effectively
iii) Alveolar macrophage:
 Much bigger than Type II cells
 Can be free in alveolus or fixed to the interalveolar septum
 Has an irregular nucleus and prominent lysosomes
iv) Capillary endothelial cell:
 Line the alveolar capillaries
 Share a basement membrane with Type I cells
In order for gas exchange to occur, O2 must diffuse through the Type I cell, then through
the shared basement membrane of the Type I cell and the capillary endothelial cell, and finally
through the capillary endothelial cell where it is taken up by erythrocytes in the capillary. CO2
follows the reverse path, starting in the capillary and eventually being exhaled after diffusing
into the alveoli.
- 24 -
ANAT 261 — LAB REVIEW #8
ORAL CAVITY
In this lab, the structures of the oral cavity will be examined, including the tooth (unerupted and erupted), the tongue, and the esophagus.
The oral cavity is lined with non-keratinized stratified squamous epithelium with an
underlying layer of lamina propria, giving it a different texture and function than the keratinized
epithelium of the skin. There is a transition from the non-keratinized epithelium to the
keratinized epithelium in the lips (just before the outer surface of the lip).
TOOTH —
Un-erupted and erupted teeth look quite different histologically. Notice that in the un-erupted
tooth, the enamel is malleable enough to be sliced and included in the section, while in the
erupted tooth the enamel is far too hard to be sectioned so it must be dissolved during the
preparation of the slide.
1. Unerupted (developing) tooth:
From innermost layer to outermost layer, the structures of the unerupted tooth:
a) Developing pulp
b) Odontoblasts (arranged in a layer)
c) Predentin and dentin
d) Enamel (stains magenta due to its basophilic nature)
e) Enamel organ (of epithelial origin):
 The enamel organ functions in the formation of the enamel of the tooth
 It is composed of (from innermost to outermost layer): the Inner Dental
Epithelium (IDE), Stratum Intermedium, Stellate Reticulum, and Outer Dental
Epithelium (ODE), but does not include the enamel itself
 Ameloblasts are tall, columnar cells that are present in the IDE and serve to
synthesize and secrete enamel
 A very important structure of the unerupted tooth is the root sheath—this is the area
where the IDE and ODE merge
 The dentin-enamel junction is the point at which the dentin and enamel merge
2. Erupted tooth:
a) Clinical crown:
 Projects above the gingiva and consists of enamel and dentin
 Enamel is composed of 98-99% inorganic matrix (hydroxyapatite crystals) and is the
hardest material in the human body
 Dentin is composed of 70% inorganic matrix (hydroxyapatite crystals) and 30%
organic matrix
 The dentin is under the enamel layer, but because the enamel has been removed, the
dentin appears as the first layer of the erupted tooth
- 25 -
b) Anatomical crown:
 Consists of the clinical crown plus the gingiva
 This is the division between the crown and the root where the enamel layer ends
 The gingiva is composed of parakeratinized stratified squamous epithelium, giving
the gum a tough and resistant quality
c) Root and associated structures:
 Structures of the root: pulp, odontoblasts, dentin, cementum
 Structures associated with the root: periodontal ligament, apical foramen, alveolar
bone
 At the level of the root, we see the mucogingival junction—the area where the
parakeratin disappears and the epithelium becomes the non-keratinized oral mucosa
which continues to the cheeks and lips
 The pulp is composed of highly vascularized and innervated loose CT
 Odontoblasts form a layer of cells on the outside of the pulp and produce the
unmineralized predentin (stains pale pink), which then becomes mineralized dentin
(stains darker pink)
 A thick layer of this dentin surrounds the pulp and odontoblasts
 The cellular processes of the odontoblasts leave small canals within the dentin that
span the entire dentin layer, ending at the cementum
 The cementum runs down the outside edge of the dentin from the uppermost part of
the root to the bottom of the dentin
 It attaches the periodontal ligament to the tooth to ensure stability of the tooth
 The cementum is a hard substance that has a similar composition to bone
 It stains darkly and increases in thickness as it approaches the bottom of the tooth
 Cementocytes can be seen in the inner part of the cementum layer; these cells
synthesize the cementum
 The apical foramen is the opening at the bottom of the root allowing nerves,
lymphatics, and blood vessels to enter the pulp
 Note: In transverse sections, you may not be able to see the apical foramen and the
dentin will appear to completely encircle the pulp
 The periodontal ligament lies on the outside of the cementum and joins to the
alveolar bone, thus lending support to the root and keeping the tooth in place; it is
composed of a fibrous dense irregular CT
 Alveolar (primary) bone is the bone of the maxilla or mandible (upper or lower jaw
bone) that lies on the outside of the periodontal ligament and forms a socket in which
the tooth lies
TONGUE —
The tongue is composed of skeletal muscle which projects in all directions and appears much
less organized than skeletal muscle found elsewhere in the body. The epithelium covering the
tongue is non-keratinized stratified squamous epithelium with an underlying lamina propria,
but feels different than the walls of the cheeks because of numerous microscopic and some
macroscopic projections called papillae.
- 26 -
There are 3 types of papillae (all with non-keratinized stratified squamous epithelium):
1. Filiform papilla:
 These papillae have a pointy shape and a long, slender structure thus serving to increase
the surface area of the tongue
 There can be tiny portions of keratinized epithelium at the tips of these papillae
 There are many of them covering the surface of the tongue, giving the tongue a rough
texture and aiding in food processing
 These papilla have a thick layer of epithelium resting upon a lamina propria which projects
into the center of the structure
 There are no taste buds present in these papillae
2. Fungiform papilla:
 These papillae have a tall, narrow stalk with a bulbous head
 They are dispersed among the filiform papillae
 A highly vascular lamina propria projects into the center of the structure
 Few taste buds are present on the upper surface of the papilla but they are not present in
the sections used in our laboratory
3. Circumvallate papilla:
 The largest and least numerous of the papillae
 Taste buds are present in the epithelial layer (stain lighter in color)
 Again, lamina propria projects into the center of the structure
 The papillae are surrounded by a groove formed by the folded epithelium
 Serous von Ebner glands are found under these papillae; they secrete lipase into the groove
of the papilla (involved in lipid digestion)
ESOPHAGUS —
The esophagus connects the oral cavity to the digestive tract and has an abundance of smooth
muscle. The esophagus has specific characteristics:
i) Mucosa:
 Epithelium – non-keratinized stratified squamous epithelium; protects the esophagus
 Lamina propria – loose CT
 Muscularis mucosa – 1 layer of longitudinally arranged smooth muscle that is most
dense in the esophagus
ii) Submucosa:
 Composed of dense irregular CT with an abundance of thick collagen and elastic fibers
 Contains mucous-secreting esophageal glands
iii) Tunica Muscularis:
 Consists of 2 layers of muscle: the inner circular layer and the outer longitudinal layer
 Composed of skeletal muscle in the upper 1/3 and smooth muscle in the remaining 2/3
 These muscles are responsible for gut motility (peristalsis and segmentation)
iv) Adventitia:
 A thick layer of fibrous dense irregular CT surrounding the esophagus
- 27 -
ANAT 261 — LAB REVIEW #9
DIGESTIVE TRACT
The digestive tract is responsible for digestion and absorption of nutrients from foods. It
has a specific organization with distinct histological features in each of its sections. In this lab,
we will be studying several sections of the digestive tract: the esophagus, stomach, small
intestine, and colon. While the colon maintains the same structural plan, the other sections of the
GI tracts are subdivided into different regions which appear distinct under the microscope. The
entire tract follows a similar plan or organization:
Mucosa
↓
Submucosa
↓
Tunica Muscularis
↓
Adventitia (esophagus) OR Serosa (rest of GI tract)
ESOPHAGUS —
The esophagus is a short tube connecting the oral cavity to the stomach, thus allowing the
passage of food from the mouth to the stomach via peristalsis. The esophagus has specific
characteristics:
v) Mucosa:
 Epithelium – non-keratinized stratified squamous epithelium; serves to protect esophagus
 Lamina propria – loose CT
 Muscularis mucosa – 1 layer of longitudinally arranged smooth muscle above the
submucosa
vi) Submucosa:
 Composed of dense irregular CT with an abundance of thick collagen and elastic fibers
 Contains mucous-secreting esophageal glands
vii) Tunica Muscularis:
 Consists of 2 layers of muscle: the inner circular layer and the outer longitudinal layer
 Composed of skeletal muscle in the upper 1/3 of the esophagus and smooth muscle in the
remaining 2/3
 These muscles are responsible for motility (peristalsis and segmentation)
viii) Adventitia:
 Thick layer of fibrous dense irregular CT surrounding the esophagus
- 28 -
STOMACH —
The stomach functions mainly to break down and add acid to incoming food to form an acidic
mixture known as chyme. It then stores the chyme until the small intestine is ready to continue
further breakdown and absorption. The stomach is subdivided into the cardia, fundus, body, and
pylorus regions. These regions differ in the characteristics of the mucosa layer. In the lab, we
will see sections of the fundus and body which have the same characteristics, as well as the
pylorus which is distinct from the other regions (we will not see the cardia region).
i) Mucosa:
 FUNDUS AND BODY:
 Epithelium – Simple columnar epithelium that is folded forming pits and glands
called gastric glands, which secrete an acidic mixture called gastric juice
 The pit is the upper region of the gastric gland:
 It is composed of tall columnar surface mucous cells
 These cells have basal nuclei and secrete mucous into the lumen of the
stomach to offer protection from its acidic contents
 The gland is the lower region of the gastric gland that dumps its contents into the pit;
it can be further subdivided into the neck and the base:
 Neck: contains mucous neck cells which secrete mucous (thick cells with
basal nuclei) and parietal cells which produce and secrete HCl and intrinsic
factor (stain bright pink and ‘look like fried eggs’)
 Base: this region stains more darkly than the neck, and consists of parietal
cells as well as zymogenic cells/chief cells which contain enzyme
precursors/proenzymes/zymogens needed for food breakdown (basal nuclei
and granulated cytoplasm)
 Also present in the neck and the base of the gland are enteroendocrine
cells/argentaffin cells—they secrete hormones that regulate gastric
secretions, which then control food breakdown and digestion (Ex: Gastrin
and Somatostatin, among others)
 In the fundus and body, the pit region is very small while the gland region is quite
prominent (pit to gland ratio is 1:3)
 Lamina propria – loose CT found between the gastric glands as well as between the
base of the gland and the muscularis mucosa
 Muscularis mucosa – a layer of longitudinal smooth muscle above the submucosa
 PYLORUS:
 Epithelium – Simple columnar epithelium also folded into pits and glands called
pyloric glands
 The pit is the upper region of the pyloric gland:
 This region is lined with surface mucous cells that secrete mucous
 The gland region below the pit empties its contents into the pit:
 Tubular in shape and surrounded by mucous cells (no parietal cells)
 Also has enteroendocrine cells scattered between the mucous cells
 In this area of the stomach, the pit region occupies a much larger area than in the
fundus and body (pit to gland ratio is 2:1)
 Lamina propria – same as in the fundus and body regions
 Muscularis mucosa – same as in the fundus and body region
- 29 -
ii) Submucosa:
 A thin layer of dense irregular CT lacking glands
iii) Tunica Muscularis:
 Consists of 3 layers of smooth muscle: internal oblique layer, middle circular layer, and
external longitudinal layer
iv) Serosa:
 A layer of dense irregular CT resting on a layer of mesothelial cells
NOTE: parietal cells are present only in the gland region of the gastric glands (in the fundus and
body regions)—NOT in the pit region of the gastric gland nor in any part of the pyloric gland
______________________________________________________________________________
SMALL INTESTINE —
The small intestine is responsible for terminal digestion of food coming from the stomach, as
well as absorption of nutrients at the surface of its mucosa. It is subdivided into the duodenum,
the jejunum, and the ileum. These regions *differ in the characteristics of the submucosa*.
Sections of the duodenum and the jejunum will be studied; however, the ileum will not be tested
on the lab exam.
DUODENUM
i) Mucosa:
 Epithelium – Simple columnar epithelium forming projections called villi, as well as
intestinal glands which are invaginations called crypts of Lieberkühn
 The villi:
 Consist of few goblet cells and many enterocytes/absorptive cells involved in
absorption of nutrients (columnar cells with a brush border/microvilli)
 The crypts:
 Consist of mainly enterocytes/absorptive cells with goblet cells, stem cells,
enteroendocrine cells, and Paneth cells (contain zymogen granules/enzyme
precursors/proenzymes) which stain lighter than the cells of the crypts
 Paneth cells are columnar cells with basal nuclei and granular cytoplasm
located at the base of the crypts. They secrete lysozyme.
 Stem cells reside at the base of the crypts and are constantly regenerating in
order to replace the cells that shed from the tips of the villi
 Lamina propria – highly vascularized loose CT pushes up into the center of the villus;
note the presence of few loosely scattered smooth muscle cells in the lamina propria
within the villi
 Muscularis mucosa – a single layer of longitudinal smooth muscle
ii) Submucosa:
 Composed of dense irregular CT
 Contains mucous Brunner’s glands which secrete an alkaline fluid to help neutralize the
highly acidic chyme coming from the stomach
iii) Tunica Muscularis:
 Has 2 layers: inner circular layer and outer longitudinal layer
iv) Serosa:
 Layer of dense irregular CT covered by a layer of mesothelial cells
- 30 -
JEJUNUM
i) Mucosa:
 Epithelium – Simple columnar epithelium forming villi and crypts (epithelium has the
same composition as in the duodenum, but with a few more goblet cells)
 Lamina propria – loose CT
 Muscularis mucosa – a single layer of longitudinal smooth muscle
ii) Submucosa:
 Consists of dense irregular CT but lacks glands, unlike the duodenum
 The plicae circularis (also called valves of Kerckring) is most developed in the
jejunum—it a series of ridge-like folds formed by the mucosa and submucosa
iii) Tunica Muscularis:
 Has 2 layers: inner circular layer and outer longitudinal layer
iv) Serosa:
 Layer of dense irregular CT covered by a layer of mesothelial cells
ILEUM
i) Mucosa:
 Epithelium – Simple columnar epithelium forming villi and crypts, with villi having a
more pointed, finger-like appearance (epithelium has the same composition as in the
duodenum, but with many more goblet cells)
 Lamina propria – loose CT
 Muscularis mucosa – a single layer of longitudinal smooth muscle
ii) Submucosa:
 Consists of dense irregular CT lacking both glands and a prominent plicae circularis
iii) Tunica Muscularis:
 Has 2 layers: inner circular layer and outer longitudinal layer
iv) Serosa:
 Layer of dense irregular CT covered by a layer of mesothelial cells
______________________________________________________________________________
COLON (LARGE INTESTINE)—
The histological characteristics remain the same throughout the colon, so it is important to
differentiate this structure from other areas of the digestive tract (mainly the small intestine).
i) Mucosa:
 Epithelium – Simple columnar epithelium forming only long straight crypts without villi
 The epithelium consists of enterocytes, abundant goblet cells, and few enteroendocrine
cells, but lacks Paneth cells
 Lamina propria – loose CT
 Muscularis mucosa – a single layer of longitudinal smooth muscle
ii) Submucosa:
 Consists of dense irregular CT, with neither glands nor plicae circularis
iii) Tunica Muscularis:
 Has 2 layers: inner circular layer and outer longitudinal layer
 Outer longitudinal layer forms 3 thick bands that surround the colon called the taenia coli
iv) Serosa:
 Layer of dense irregular CT covered by a layer of mesothelial cells
- 31 -
*A note on sectioning of slides:
The section of the smooth muscle layers of the Tunica Muscularis allow you to tell if the tissue
you are studying was cut in cross section or longitudinal section. Examine the outer longitudinal
layer of smooth muscle: if this layer appears in longitudinal section, the tissue was sectioned
longitudinally. If, however, the outer longitudinal layer appears in cross section, the tissue was
sectioned in cross section.
- 32 -
ANAT 261 — LAB REVIEW #10
ASSOCIATED GLANDS
In this lab we will be studying several of the glands associated with the functioning of the
GI tract; namely the 3 salivary glands, the pancreas, and the liver. Before discussing these glands
in detail, we will review the classification of glands.
Glands are classified according to the following criteria:
i) The number of cells:
 Unicellular – consists of one cell
Ex: Enteroendocrine cells of the GI tract, goblet cells
 Multicellular – consists of more than one cell
Ex: Salivary glands or any gland consisting of more than one cell
ii) The destination of the secretion:
 Exocrine — product goes to external environment; gland has a duct
Ex: Sweat gland, salivary glands
 Endocrine — product goes directly into the blood; gland is ductless
Ex: Thyroid gland, Islets of Langerhans (pancreas), adrenal gland
iii) The way the secretion leaves the cell:
 Merocrine — cell remains intact upon secretion
Ex: Sweat gland, exocrine pancreas
 Apocrine — part of cell is secreted, but cell does not die
Ex: Mammary gland
 Holocrine — cell dies and its contents are secreted
Ex: Sebaceous gland
iv) The type of duct:
 Simple — unbranched
Ex: Sweat gland
 Compound — branched
Ex: Salivary glands
v) The appearance of the secretory portion:
 Acinar — spherical collection of cells
Ex: Mucous acini (mucous secretions) or serous acini (serous secretions)
 Tubular —long, tube-like structure
Ex: Sweat gland, gastric glands
- 33 -
SALIVARY GLANDS (3) –
The functions of the salivary gland include wetting the oral cavity and incoming food, as well as
initiating breakdown and digestion of carbohydrates. The secretion of the salivary gland has many
ingredients and is collectively known as saliva. Some of these ingredients are enzymes like
salivary amylase, lysozyme, and lactoferrin, as well as the antibody IgA.
CLASSIFICATION OF THE SECRETORY PORTION OF THE SALIVARY GLANDS:
a) Mucous acini have large cuboidal/columnar cells that stain quite pale and also have dark,
flattened basal nuclei. They secrete a thicker, more viscous substance.
b) Serous acini consist of smaller pyramidal cells that stain darkly, with pale circular basal
nuclei. These acini secrete a non-viscous, proteinaceous secretory product. The serous acini
are surrounded by contractile myoepithelial cells which aid in propulsion of the saliva to
the secretory ducts.
c) Seromucous acini have a large mucous portion (stains pale) with a crescent-shaped serous
portion (stains darker) called a serous demilune. The serous demilunes of the seromucous
acini are surrounded by myoepithelial cells.
NOTE: all mucous and serous secretory epithelial cells of the acini rest on a basement membrane
STRUCTURE AND ORGANIZATION OF THE SALIVARY GLANDS (from outside to inside):
 The entire gland is surrounded by a capsule of dense irregular CT
 The gland is composed of many divisions called lobes which are then further subdivided into
smaller sections called lobules
 Each lobule is separated by an extensive septum of connective tissue called interlobular CT
 Because this is an exocrine gland, its secretions travel to the oral cavity via an extensive
network of ducts:
 Intralobular ducts: (ducts within the lobules of the gland; eventually empty into the
interlobular ducts)
 Intercalated duct: lined with simple, short cuboidal epithelial cells resting on a
basement membrane; these are the first ducts coming off the acini and empty into
the striated ducts
 Striated/secretory duct: lined by simple columnar epithelial cells with longitudinal
striations due to mitochondria at the base of the cells; empty into interlobular ducts
 Interlobular ducts: lined by simple columnar epithelium and are located between the lobules
in the interlobular CT; empty into the interlobar ducts of the gland
 Interlobar ducts: very large ducts that travel between the lobes of the gland within the
interlobar CT; eventually drain into the main excretory duct of the gland which then empties
into the oral cavity
THE 3 SALIVARY GLANDS:
1. Parotid gland:
 Located in the cheek, this gland is composed of serous acini
 These acini stain darkly due to the presence of zymogen granules at the apical part of the
pyramidal-shaped cell
 The myoepithelial cells surrounding the acini function to contract and push the contents of
the acini into the ducts of the gland
 Secretory product is rich in salivary amylase and IgA antibody
- 34 -
2. Submandibular (submaxillary) gland:
 Located beneath the mandible (lower jaw bone), this gland consists of serous acini as well
as seromucous acini
 The majority of the acini are actually serous acini, with many of the mucous acini having
serous portions called serous demilunes (in the shape of a crescent)
 Secretory product is rich in lysozyme and lactoferrin
3. Sublingual gland:
 Located under the tongue and is covered by the oral mucosa of the oral cavity
 This gland consists mainly of mucous acini, with few serous cells appearing as serous
demilunes on the mucous acini
 The mucous acini stain pale due to the presence of mucin granules in the cytoplasm of the
mucous cells
 Secretory product is rich in lysozyme
NOTE: The prefix ‘intra’ refers to within the structure itself (Ex: intralobular ducts are
ducts within the lobules of the gland).
The prefix ‘inter’ refers to between structures (Ex: interlobular ducts are ducts
between the lobules of the gland)
_______________________________________________________________
PANCREAS –
The pancreas is a compound acinar gland with both an exocrine portion and endocrine portion.
The exocrine portion is composed of serous acini (similar to the parotid gland) which secrete
digestive enzymes into the duodenum. The endocrine portion is composed of the Islets of
Langerhans that secrete hormones into the bloodstream.
1. Exocrine pancreas:
 The functional unit of the exocrine pancreas is the pancreatic acinar cell, which is grouped
into serous acini within the gland
 The acini stain darkly due to zymogen granules at the apical pole of the cell and have basal
nuclei
 Unlike in the salivary gland, the serous acini of the exocrine pancreas do not have
myoepithelial cells
 Note the presence of centroacinar cells in the center of the acini
 These cells have a pale-staining cytoplasm and lack granules. They are derived from the
cells of the intercalated ducts of the pancreas
The ducts:
 Intralobular ducts (connect the acini):
 Intercalated ducts: lined with simple, short cuboidal epithelial cells and are the
only type of intralobular duct in the pancreas; empty into interlobular ducts.
Note that there are *no striated ducts* in the pancreas
 Interlobular ducts: lined with simple cuboidal epithelial cells and are surrounded by the
interlobular CT; these ducts eventually coalesce to form the main pancreatic duct which
empties directly into the intestine
- 35 -
 Regulation of the exocrine pancreas:
 Controlled by the enzymes secretin and CCK (cholecystokinin) allowing it to adjust
the level of secretion as needed
 Secretions of the exocrine pancreas:
 Secretes pancreatic juice (digestive enzymes and sodium bicarbonate) into the lumen
of the duodenum to aid in digestion and neutralization of the acidic chyme
 Some of the enzymes are secreted as proenzymes/enzyme precursors and only
become activated in the intestine, while others are secreted as active enzymes
 Enzymes include: proteases [trypsinogen, procarboxypeptidase, proelastase], lipases
[prophospholipase A], amylases, nucleases [DNase, RNase]
**It is important to differentiate the salivary glands from the exocrine pancreas:
THE SALIVARY GLANDS
vs.
THE EXOCRINE PANCREAS
Striated ducts
NO striated ducts
Mucous and serous acini
ONLY serous acini
NO centroacinar cells
Centroacinar cells
NO Islets of Langerhans
Islets of Langerhans
2. Endocrine pancreas (Islets of Langerhans):
 The Islets of Langerhans are round, pale-staining clusters of cells lodged within the
exocrine portion of the pancreas and surrounded by a thin capsule of dense irregular CT
 As an endocrine gland, this portion of the pancreas does not have ducts and secretes
hormones directly into the blood
 As such, there are many fenestrated capillaries within the Islets of Langerhans to allow for
the passage of these hormones into the blood
 Mainly contains cells that secrete glucagon (α cells) and insulin (β cells), but also has cells
that secrete somatostatin (δ cells)
_______________________________________________________________________________
LIVER –
The liver is the largest gland in the body with its functional unit being the liver epithelial cell
called the hepatocyte. Some of the functions of the liver include removing substances from the
blood coming from the GI tract, storing lipids and carbohydrates, and producing bile (involved in
fat digestion). In the GI tract, many macromolecules are absorbed into the blood; however, before
this blood can pass into circulation it must first be filtered to rid the blood of toxic or
overabundant materials. In this filtration process, macromolecules are taken up by the liver and
enzymatically modified, and are then returned to the bloodstream.
BLOOD FLOW TO THE LIVER:
1. The systemic/arterial supply:
The arterial supply consists of the hepatic artery coming from the heart, which branches
into hepatic arterioles that supply the individual hepatic lobules. They are located in the
portal space. The blood from the hepatic arterioles reaches the hepatocytes via fenestrated
capillaries called sinusoids, which converge to form the central vein in the center of each
lobule. These vessels provide oxygen and nutrients to the hepatocytes.
- 36 -
2. The portal supply:
The portal supply consists of the portal vein which drains from the lower part of the GI
tract (intestines). By definition, a portal system begins and terminates in a bed of
capillaries; here, the portal veins begin in the lower portion of the GI tract as a network of
capillaries which then converge to form one portal vein that enters the liver. Once in the
liver, the portal vein branches into portal venules which carry blood to the hepatocytes
via the fenestrated capillaries called sinusoids. The portal venules are also located in the
portal space. These sinusoids converge to form the central vein which is located in the
center of each lobule. The blood in the central vein drains into the sublobular vein,
which then empties into the hepatic vein. Finally, the blood drains from the hepatic vein
into the inferior vena cava to be recirculated by the heart (after being oxygenated in the
lungs). The system offers a direct route for materials from the intestines to the liver
without first being returned to the heart and recirculated throughout the entire body.
STRUCTURES AND ORGANIZATION OF THE LIVER:
 The entire gland is surrounded by a capsule of dense irregular CT
 It is divided into lobes, which are further divided into hepatic lobules:
 Many hexagonally-shaped lobules; each lobule is separated by dense irregular CT
 Each lobule is composed of cells called hepatocytes as well as sinusoids (irregular
capillaries lined with fenestrated endothelial cells), with a central vein in its center
 The sinusoids serve to connect the portal venule and the hepatic arteriole to the
central vein
 The blood and the bile circulate in 2 different systems within the lobules:
a) Blood circulates from the periphery of the lobule to the center (from the portal space to
the sinusoids and then to the central vein)
b) Bile circulates from the center of the lobule to the periphery:
 Located between adjacent hepatocytes, tiny channels called bile canaliculi carry
the bile produced by the hepatocytes
 While still remaining between adjacent hepatocytes, these bile canaliculi will bend
and drain into the cholangiole, which then empties into the bile duct
 Cholangiole: lined with low cuboidal or squamous cells (it is analogous to the
intercalated duct of the salivary glands or pancreas)
 Bile duct: lined by cuboidal/columnar epithelium with lightly-strained cytoplasm
and darkly-stained central nuclei; empties into the right and left hepatic ducts
which eventually drain into the gall bladder via the common bile duct
 At the junction of adjacent lobules, there is an enlargement of CT called the portal space:
 There are 3 structures present in the portal space:
1. Bile duct:
 Has very round, centrally-located nuclei
 Cholangioles can often be spotted near the bile duct—they are much smaller
than the bile duct and their nuclei stain the same color as those of the duct
2. Hepatic arteriole (branch of the hepatic artery):
 Has a thicker wall than the bile duct and the portal venule
3. Portal venule (branch of the portal vein):
 Has a very thin wall and has a larger lumen than both the hepatic arteriole and
the bile duct
- 37 -
ANAT 261 — LAB REVIEW #11
URINARY SYSTEM
The urinary system consists of the kidneys, the ureters, the urinary bladder, and the
urethra. This system has several important functions including regulation of total body water,
maintenance of ionic balance, excretion of soluble metabolic wastes, and secretion of hormones
(Renin and Erythropoietin).
The nephron is the functional unit of the kidney consisting of both coiled and straight
tubes of varying sizes located partly in the cortex and partly in the medulla. The cells of this tube
constantly filter the blood and allow for the excretion of wastes as well as the recycling of useful
substances. The first part of the nephron is the renal corpuscle which serves to filter the blood
through a network of extensive fenestrated capillaries. The Proximal Convoluted Tubule (PCT)
stems from the urinary pole of the renal corpuscle and leads into the Loop of Henle. The Loop of
Henle is composed of (i) the thick straight descending limb, (ii) the thin ascending limb, and (iii)
the thick straight ascending limb. This thick straight ascending limb transitions into the Distal
Convoluted Tubule (DCT), whose end marks the end of the nephron. The collecting tubules and
then collecting ducts of Bellini form from the DCT, however they are not considered part of the
nephron. The area cribosa is the opening of the collecting ducts into the minor calices of the
kidney.
Area cribosa
- 38 -
KIDNEY –
Each kidney is surrounded by a capsule of dense irregular CT and is divided up into 2
histologically distinct regions:
1. Cortex:
 This is the outer region of the kidney that stains darker than the inner region
 The structures of the cortex are:
i) Renal corpuscle:
 Composed of (i) a ball of capillaries called the glomerulus which serves to filter
the blood entering the corpuscle, and (ii) a round structure surrounding the
glomerulus called Bowman’s capsule
 The renal corpuscle has a vascular pole where the blood vessels enter, as well as
a urinary pole where the glomerular filtrate exits via the PCT
 The blood enters at the vascular pole via the afferent arteriole, which then
branches into an extensive network of coiling fenestrated capillaries, and finally
exists the vascular pole via the efferent arteriole
 Bowman’s capsule consists of:
a) An outer parietal layer composed of simple squamous epithelial cells
 This layer is continuous with the cells of the PCT which exit the corpuscle
at the urinary pole
b) A layer of basement membrane
c) An inner visceral layer composed of specialized cells called podocytes
which surround the capillaries within the glomerulus
 The secondary cellular processes of the podocytes (called pedicels) form
finger-like projections that wrap around the capillaries and create gaps
called filtrations slits
 The basement membrane of the podocytes is shared with the basement
membrane of the endothelial cells lining the capillaries
 There is a large space within the Bowman’s capsule called the Bowman’s
space/capsular space/urinary space which collects the filtrate coming from the
fenestrated capillaries of the glomerulus
ii) Proximal convoluted tubule (PCT):
 Originates from the urinary pole of the renal corpuscle and is the first tube to
carry the glomerular filtrate out of the glomerulus
 Composed of darkly-staining cuboidal cells that have striations due to folding of
the plasma membrane around mitochondria
 Cells have a brush border (microvilli) to increase surface area for absorption of
fluids and proteins
 Cells have centrally located nuclei, and lack clear membranes between adjacent
cells
 The tubules have partially occluded and cloudy lumens
iii) Distal convoluted tubule (DCT):
 As compared to the PCT, the cell of the DCT have fewer striations, a more sparse
brush border
 These cells have a less acidophilic cytoplasm than those of the PCT and therefore
they stain a lighter color
- 39 -
 Also in contrast with the PCT, the DCT lumen appears clean and empty
 These cuboidal cells have their nuclei close to the apical/luminal membrane
(they are said to be ‘kissing the apical membrane’)
 Again, plasma membranes between cells are not visible
 An important region of the DCT is the Macula Densa, which is the area of the
DCT that is extremely close to the afferent arteriole
 The Macula Densa is part of the Juxtaglomerular Apparatus (discussed below)
 In this area, the DCT cells are densely packed large columnar cells
 This area of the nephron is the site of Aldosterone action (increases uptake of
Na+, and therefore the absorption of H2O)
iv) Collecting tubules:
 This is the continuation of the DCT, but is the first tubule that is not considered
part of the nephron
 It is lined by cuboidal cells with central nuclei and visible lateral membranes
between cells
 These tubules increase in diameter as they move away from the cortex
v) Medullary rays:
 These are striated projections of the medulla within the cortex
 These rays consist of collecting tubules as well as the thick straight descending
limbs and thick straight ascending limbs of the Loop of Henle
2. Medulla:
 This is the inner region of the kidney and stains paler than the cortex
 This area has a striated appearance due to the presence of the straight tubules of the Loop
of Henle as well as the thick collecting ducts (not part of the nephron)
 These structures are grouped into pyramid-shaped sections called medullary pyramids,
which are separated by interlobar dense irregular CT called Columns of Bertin
 Interlobar arteries can be found within this interlobar CT
 The structures of the medulla are:
i) Loop of Henle:
 Thick straight descending limb – same appearance as the PCT
 Thin ascending limb – resembles a capillary, but has a larger empty lumen
 This section of the Loop of Henle is highly permeable to Na+
 Thick straight ascending limb – same appearance as the DCT
ii) Collecting ducts of Bellini:
 Consists of large columnar cells with centrally located nuclei
 The plasma membranes separating cells is very visible in these ducts
 This is the site of ADH/Vasopressin action, which increases H2O resorption by
stimulating the insertion of aquaporins (water channels) into the membrane, thus
increasing the membrane’s permeability to H2O
iii) Vasa recta:
 Long capillaries arising from the efferent arterioles which have an arterial end and
a venous end
 Vasa recta run close to the thin ascending limb of the Loop of Henle and are
located only at the level of the medulla
 Vasa recta are involved in providing oxygen and nutrients to the medulla
- 40 -
iv) Major Calyces and minor Calyces:
 These are areas which collect the concentrated urine after it has passed through
the nephron
 The area cribosa at the apex of the medullary pyramids drains the urine from the
collecting ducts into the minor Calyces, which then drain into the major Calyces
 A widening of the ureter called the renal pelvis collects the urine from the major
calyces and empties it into the ureters
 Note: singular = calyx
THE JUXTAGLOMERULAR APPARATUS:
 An important structure located in the cortex, it consists of:
i) Macula Densa:
 The region of the DCT with large columnar cells
ii) Juxtaglomerular cells:
 These are the cells of the afferent arteriole that are close to the Macula Densa
 They are modified endocrine cells which release secretory granules containing
hormones (Renin, Erythropoietin) into the capillaries of the glomerulus in response
to physiological stimuli (not seen in this lab)
iii) Extraglomerular mesangial cells:
 These cells are located in the region of the vascular pole of the renal corpuscle
between the Macula Densa and the afferent and efferent arterioles (just outside the
glomerulus)
BLOOD SUPPLY OF THE KIDNEY: (Identification of blood vessels is not required in this lab)
Oxygenated blood coming from the heart enters the hilum of kidney via the renal artery,
which then proceeds to branch into the smaller arteries interlobar arteries that run in the
interlobar CT. The interlobar arteries branch at right angles into the arcuate arteries which
run horizontally along the cortico-medullary junction. The arcuate arteries then branch into
the interlobular arteries, which branch at right angles and travel upwards until they branch
again into the afferent arterioles that lead into the glomerulus at the vascular pole. Once
inside the glomerulus, the afferent arteriole gives rise to the fenestrated capillaries, which
then coalesce to form the efferent arteriole that exits the glomerulus again at the vascular
pole. The efferent arteriole can then either:
- 41 -
URINARY BLADDER –
The urinary bladder is a muscular compartment that serves as a reservoir for urine until it can be
excreted from the body via the urethra.
 It is composed of several layers:
i) Mucosa:
 The layer closest to the lumen is composed of transitional epithelium which is
characterized by bulgy, polygonal-shaped surface cells called facet cells/dome cells
 This number of layers of epithelium varies depending on the amount of urine in
the bladder
 When there is more urine in the bladder there are fewer cell layers, while when
there is less urine in the bladder there are more cell layers
 The epithelium is able to expand in order to accommodate increasing volumes of
urine
 A thin layer of lamina propria is present beneath the epithelial layer
ii) Submucosa:
 A layer of dense irregular CT that lies below the mucosa
iii) Tunica muscularis:
 Composed of 3 layers of smooth muscle as well as some dense irregular CT
 The smooth muscle layers appear as: inner longitudinal, middle circular, and outer
longitudinal
- 42 -
ANAT 261 — LAB REVIEW #12
NERVOUS TISSUE
In this lab, we will examine some structures of the Central Nervous System (CNS) as
well as of the Peripheral Nervous System (PNS). Multipolar neurons will be seen in sections of
the CNS; these neurons are defined as having more than two cellular processes (i.e. one axon and
many dendrites). These cells include pyramidal cells in the brain cortex, Purkinje cells in the
cerebellum, and motor neurons in the ventral horn of the spinal cord. In addition, peripheral
nerves of the PNS will be studied.
The nervous system is divided into the CNS, which is composed of the brain (cerebrum
and cerebellum) and spinal cord, and the PNS which includes all other nervous tissue in the body
(nerve fibers and nerve ganglia) outside of the CNS. The functional unit of the nervous system is
the neuron (or nerve cell) as it receives, transmits, integrates and processes various stimuli. A
nerve is a collection of the nerve cell fibers (axons) that conduct sensory or motor impulses
towards and away from the CNS.
Furthermore, the CNS is composed of two morphologically different types of nervous
tissue: grey matter and white matter. The grey matter is composed of the cell
bodies/somas/perikaryon of neurons, dendrites, unmyelinated axons, as well as different types of
neuroglia. The white matter is composed of the myelinated axons of neurons as well as
neuroglia, but lacks neuronal cells bodies. It is the myelin sheath covering the axon that gives the
white matter its lighter appearance. The organization of the grey and white matter is reversed in
the brain (cerebral cortex and cerebellum) and the spinal cord—in the brain the grey matter is on
the periphery with white matter in the center, while in the spinal cord the grey matter is central
and the white matter is peripheral.
Nerve tissue consists of a small amount of extracellular matrix (ECM), as well as 2 types of
cells:
1. Nerve cells/neurons:
 The cell body (also called the soma or the perikaryon) of the neuron has a large round
nucleus, a prominent nucleolus, as well as eukaryotic cellular organelles
 Dendrites are projections of the perikaryon that receive incoming messages from other
neurons
 There is also one longer projection called an axon that is connected to the cell body via
a pyramid-shaped region called the axon hillock. Axons can be myelinated or
unmyelinated; the myelinated axons have gaps in the myelin sheath called Nodes of
Ranvier which allow for the propagation of electrical impulses along the axon.
 Nissl bodies are darkly-staining granules occupying the cytoplasm of the perikaryon
and dendrites, but not of the axon hillock. These granules consist of RER and free
ribosomes, thereby acting as a site of protein synthesis in the neuronal cell body.
 Lipofuscin pigment granules are found in the cell bodies of the ganglion cells
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2. Glial cells/neuroglia (not studied in the lab):
 These cells serve to support, protect, and nourish the nerve cells
 There are several different types of neuroglia that perform different functions; you will
not be responsible for identifying the specific neuroglial cell in the nervous tissue,
however you will have to identify cells as general glial cells
 The 4 types of neuroglia:
a) Astrocytes:
 Found in the white matter of the CNS, these cells form and maintain the
blood-brain barrier, as well as regulate ion and neurotransmitter
concentrations
b) Oligodendrocytes:
 Found in the white matter of the CNS, these cells are responsible for
producing the myelin that covers the axons of the white matter
c) Schwann cells:
 Found in the PNS, these cells produce the myelin sheath covering the axons in
the white matter
 Unmyelinated axons in the PNS reside in the clefts of Schwann cells
d) Microglia:
 Found throughout the CNS, these small neuroglia have a phagocytic function
as they clear the damaged structures in the CNS
CENTRAL NERVOUS SYSTEM:
CEREBRAL CORTEX –
The cortex is the convoluted outer layer of grey matter surrounding the cerebrum. Recall that in
the brain, the white matter is located below the grey matter (not seen in the slides).
 In this region there are many pyramidal neurons, which are a type of multipolar neuron with
a pyramid-shaped cell body
 Also present in this region are glial cells
 The pia mater (one of the meninges of the central nervous system) surrounds the outer surface
of the cerebral cortex
CEREBELLUM –
The cerebellum has the same organization of grey and white matter as the cerebral cortex (i.e. the
cerebellar cortex is composed of grey matter while the central part of the cerebellum is
composed of white matter). There are 2 layers of grey matter in the cerebellar cortex that are
separated by a layer of Purkinje cells:
1. Molecular layer (outer layer):
 A more sparse looking layer containing the dendrites of the Purkinje cells
 Purkinje cells have an extensive network of branching dendrites that take up much space
in this layer, therefore explaining the sparseness of the nuclei
2. Granular layer (inner layer):
 The granular layer is extremely dense and contains the axons that extend from the
Purkinje cell body
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 The cell body of the Purkinje cell is lodged in the border between the molecular layer and the
granular layer, but is closer to the granular layer
 The Purkinje cells appear quite distinct on the border of these two layer with their large,
round cell bodies
 The white matter is located central to both of these layers of grey matter
SPINAL CORD –
There are two regions in the spinal cord:
1. The more superficial region of the spinal cord consists of white matter which is lighter in
appearance
 The predominant structures in this layer are myelinated axons which appear as small
tubes surrounded with a thick white layer of myelin
2. Deep to the white matter lies the grey matter, a darker H-shaped region in the center of the
spinal cord
 Many multipolar neuron cell bodies can be seen in the ventral horns
 Note the distinct shape of the cell body, the prominent Nissl bodies in the perikaryon
and dendrites, as well as the dense nucleoli of these neurons
 At the center of this H-shaped region lies the central canal/ependymal canal lined with
ependymal cells
 Neuroglia are present in both white and grey matter
 Note also that there is an anterior aspect and a posterior aspect of the spinal cord
PERIPHERAL NERVOUS SYSTEM:
PERIPHERAL NERVE –
In the PNS, axons are grouped together in bundles to form peripheral nerves. This term refers to
bundles of nerve fibers outside the CNS. These peripheral nerves are composed of:
 Groupings of many bundles of myelinated axons (myelinated by Schwann cells)
 Several of these bundles grouped together are surrounded by a fibrous layer of dense irregular
CT called the epineurium
 Each bundle within this group of bundles is surrounded by another layer of dense irregular CT
called the perineurium
 Finally, each individual axon is surrounded by a thin layer of dense irregular CT called the
endoneurium, composed of reticular fibers and fibrocytes
 Most peripheral nerves consist of bundles of sensory fibers which relay information from the
PNS to the CNS, as well as motor fibers which relay information from the CNS to the PNS
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SUMMARY OF TYPES OF EPITHELIUM AND THEIR LOCATIONS —
A. Simple epithelium [1 cell layer]
i) Simple Squamous Epithelium:
 Thin flat cells with little intercellular space
 Found in: Endothelium (the epithelium that lines blood vessels)
Bowman’s capsule of the renal corpuscle (kidney)
ii) Simple Cuboidal Epithelium:
 Cells appear to be nearly square with approximately central nuclei
 Found in: Distal convoluted tubule of kidneys
Collecting ducts of kidneys
iii) Simple Columnar Epithelium:
 Tall cells with basal nuclei which are all at the same level
 Usually have either an absorptive or secretory function; found lining much of the
digestive tract and larger ducts of glands
 Found in: Lining of the GI tract (with goblet cells and brush border)
iv) Pseudostratified Ciliated Columnar Epithelium:
 Similar to simple columnar epithelium, but nuclei are at different levels
 Found in: Lining of the trachea (with goblet cells)
B. Stratified Epithelium [more than 1 layer of cells]:
i) Stratified Squamous Epithelium:
 Cellular layer composed of squamous epithelium with many layers of cells
 May be either keratinized or non-keratinized
 Found in: Surface of tongue (non-keratinized)
Skin (keratinized)
ii) Stratified Cuboidal Epithelium:
 Like simple cuboidal, but has more than 1 layer of cuboidal cells
 Found in: Lining of excretory ducts of the sweat gland
Lining of secretory ducts of salivary glands
iii) Stratified Columnar Epithelium:
 Like simple columnar, but has more than 1 layer of columnar cells
 Found in: Lining of the ducts of large salivary glands
(i.e. Submandibular gland)
C. Transitional Epithelium:
 The number of layers of the epithelium depends of the state of the bladder—there are
more layers when empty and fewer layers when full
 Found in: Urinary bladder
Renal pelvis and calyces in the kidneys
Ureter and urethra
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SUMMARY OF THE TYPES OF CT AND THEIR LOCATIONS —
A. Adipose tissue:
 Composed of fat cells
 Found in: Hypodermis of skin
Many places throughout the body where fat is concentrated
B. Loose CT:
 Highly vascular and cellular; loosely organized
 Found in: Papillary layer of dermis
Lamina propria of GI tract (and others)
C. Dense CT:
 Provides support for surrounding tissues; less cellular than loose CT
i) Dense Regular CT
 Found in: Tendon
ii) Dense Irregular CT
 Found in: Reticular layer of dermis
D. Cartilage:
 Supports surrounding tissues and provides cushion
i) Hyaline cartilage
 Found in: Trachea and larynx
Articular cartilage
Epiphyseal plate of long bones
i) Elastic cartilage
 Found in: Epiglottis
External ear
E. Bone:
 Supports tissues, facilitates movement
i) Compact bone
 Found in: Diaphyses of long bones
Outer layer of epiphyses of long bones
ii) Spongy bone
 Found in: Epiphyses of long bones
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