HISTOLOGY LAB
Introduction
Cells are arranged in organized groups called Tissues that carry out specific functions.
Tissues are organized together to form Organs, which carry out more complex functions.
Organs work together in groups to form Systems which in turn carry out a higher order function.
There are four basic types of tissues we will identify in the lab. These tissue types are:
1. Epithelium. B. Connective. C. Muscular. D. Nervous
1. EPITHELIAL TISSUE
There are two basic types of epithelial tissue:
(a) Covering and lining epithelium
- forms the outer covering of:
- external body surfaces
- some internal organs
- lines body cavities
- lines interiors of:
- respiratory tract
- gastrointestinal tract
- blood vessels
- ducts
- hollow reproductive organs and vessels
(b) Glandular epithelium
- makes up the secreting portion of glands As the illustration below shows, all
epithelial tissue adheres to a connective tissue membrane layer referred to as the Basement
Membrane. The basement membrane attaches the epithelium to the underlining connective
tissue.
The flow chart below illustrates the different types of epithelial tissue
Simple Squamous Epithelium
As the diagram and photomicrograph below (and on the next page) illustrates, this tissue
consists of a single layer of flat cells. The slide you are looking at in lab has only simple
squamous epithelium on it, so it is easy to find and identify.
Description: A single layer of flat cells. Looks like a platter of fried eggs "sunny-side up".
Location: Air sacs (alveoli) of lungs, lines the inside of heart and blood vessels.
Function: Filtration, diffusion, osmosis.
Drawing of Simple Squamous Epithelium – Superior and lateral aspects
Light Micrograph of Simple Squamous Epithelium – Superior aspect (400X)
In this view the lumen associated
with epithelium cannot be seen as
the viewer is looking down on the
top (superior aspect) of the tissue.
Notice how the nucleus is clearly
seen in the center of each cell.
Light Micrograph of Simple Squamous Epithelium – Lateral aspect (400X)
In this view of the tissue from the
side (lateral aspect) the nucleus can
still be seen but the overall shape
of the cell cannot be discerned
******************************************************************************
Simple Cuboidal Epithelium
As the drawings and photomicrographs illustrate below (and on the next page) this tissue
consists of a single layer of cube shaped cells. The slide you are looking at in lab is a slide of the
kidney. This slide has many different types of tissue on it.
Description: A single layer of roughly cube-shaped cells
Location: Lines kidney tubules and the small ducts of many glands
Function: Secretion and absorption
Drawing of Simple Cuboidal Epithelium
Notice the central location of the
nucleus in this tissue (the distance
from the nucleus to the top and
bottom of cell is about equal). The
drawing gives the impression that this
tissue is cube shaped, when in fact it
is more polyhedral in shape.
The kidney slide has a section of kidney on it that looks like this:
In this view of the kidney the
papilla can be seen. It is the
nipple-like projection extending
downward. At this low
magnification (40X) the ducts
lined with simple Cuboidal
epithelium can barely be seen.
The same structure should be viewed at a higher magnification (400X)
In this view the duct is clearly
seen. Note that the simple
Cuboidal epithelium lines the
lumen (inner space) of the duct.
Each Cuboidal cell is roughly
cubed shaped with a centrally
located nucleus.
*****************************************************************************
Simple Columnar Epithelium (non-ciliated)
On this slide you must differentiate the liver from the gall bladder in order to locate the Simple
Columnar Epithelium that lines the inside of the gall-bladder. Notice that this tissue is often
found on finger-like projections of the mucosal lining called villi.
Description: A single layer of tall rectangular cells
Location: Lines the gall-bladder and most of the G.I. tract
Function: Absorption and secretion
Drawing of Simple Columnar Epithelium – Superior and Lateral
Photomicrograph of Simple Columnar Epithelium (40X)
Remember that the slide probably has both liver and gall-bladder on it. To locate the tissue
look for the villi as illustrated below (or on the next page) on this slide of a gall-bladder.
Notice that the villi is a finger-like
projection of the mucosa that
extends into the lumen of the gallbladder (40X)
Photomicrograph of Simple Columnar Epithelium – from the Gall-bladder (100X)
The Simple Columnar Epithelium
can be seen in this
photomicrograph lining the villi of
the gall-bladder. Even at this
relatively small magnification the
position of the nuclei at the bottom
of the cell (close to the basement
membrane) can be seen.
Photomicrograph of Simple Columnar Epithelium – from the Gall-bladder (400X)
The exact shape of the columnar
cell is hard to see in this
photomicrograph. However, the
position of the nuclei in the bottom
one-third of each cell is an
identifiable characteristic.
*****************************************************************************
Stratified Squamous Epithelium
As the drawing and photomicrographs below (and on the next page) illustrate this tissue
consists of many layers of cells. The cells next to the basement membrane are columnar to
Cuboidal in shape and the cells next to the lumen are squamous in shape. Stratified tissues are
named according to the shape of the cells next to the lumen.
Description: Many layers of cells with squamous cells located next to the lumen
Location: Keratiniazed variety located on the outer surface of the epidermis of the skin. The
non-keratinized variety lines the mouth, esophagus, and vagina.
Function: Protection
Drawing of Stratified Squamous Epithelium – Superior and lateral aspect
Notice that the cells near the basement
membrane are columnar to Cuboidal in shape,
and the cells near the surface (lumen) are
squamous in shape. This tissue is named
according to the shape of the cells near the
lumen, so this is Stratified Squamous Epithelium
Photomicrograph of Stratified Squamous Epithelium – non-keratinized (40X)
At this magnification the Stratified
Squamous Epithelium appears as a
darkly stained band next to the
lumen. This is a slide of the
epidermal layer of the vagina.
Photomicrograph of Stratified Squamous Epithelium – non-keratinized (200X)
At this magnification the Stratified
Squamous Epithelium is more
obvious (it makes up the
Epidermis of the vagina).
Photomicrograph of Stratified Squamous Epithelium – non-keratinized (400X)
At this magnification of the
epidermis of the vagina the
squamous shape of the cells next
to the lumen can be seen
Photomicrograph of Stratified Squamous Epithelium – keratinized (40X)
At this magnification the Stratified
Squamous Epithelium (Epidermis)
appears as two stained bands of
cells next to the lumen. The
lighter band closer to the lumen is
composed of keratinized cells.
This type of epithelium is found on
the palms of the hands and the
soles of the feet. The keratinized
layer is the Stratum Corneum.
Photomicrograph of Stratified Squamous Epithelium – keratinized (100X)
At this magnification the stratified
nature of the Stratified Squamous
Epithelium can barely be seen.
Photomicrograph of Stratified Squamous Epithelium – keratinized (400X)
At this magnification the stratified
nature of the tissue can be
discerned.
*****************************************************************************
Pseudostratified Columnar Epithelium (Ciliated)
As the drawing and photomicrographs below (and on the following pages) illustrates, this
tissue is not really stratified (hence the prefix pseudo). Note that this tissue also has numerous
goblet cells and looks a lot like Simple Columnar Epithelium. However, unlike Simple
Columnar Epithelium this tissue is not found lining villi. The presence of cilia is an important
identification mark as this is the only ciliated tissue you will examine this quarter.
Description: Looks like a stratified tissue, but its not. Each cell extends from the basement
membrane to the lumen.
Location: Lines the upper respiratory tract, the Epididymis, and part of the male urethra.
Function: Secretion and movement of mucous by ciliary action
Photomicrograph of Pseudostratified Columnar Epithelium (Ciliated) (100X)
At this magnification the
Pseudostratified Columnar
Epithelium (Ciliated) can be seen
next to the lumen. The epithelium
has a darker stain than the underlying connective tissue.
Photomicrograph of Pseudostratifed Columnar Epithelium (Ciliated) (400X)
At this magnification the cilia is
clearly visible at the apex of the
cell (right next to the lumen).
Notice that the tissue appears to be
stratified due to the presence of
nuclei at different levels.
******************************************************************************
Transitional Epithelium
As the drawing and photomicrograph below (or on the next page) illustrates this tissue has
features common to stratified cuboidal and Stratified Squamous epithelium (hence the name
transitional. This tissue can be identified easily from two distinguishing characteristics:
1. The surface cells are scalloped.
2. In the cells next to the lumen the nucleolus can be clearly seen in the nucleus.
Description: The appearance of this tissue can vary greatly, that is why it is called
transitional epithelium.
Location: Lines the urinary bladder and Ureter
Function: Permits distention
Drawing of Transitional Epithelium – Superior and lateral aspects
This drawing illustrates the stratified
nature of this tissue. The cells next to
the lumen can be squamous, Cuboidal,
and/or columnar in shape, hence the
name transitional
Photomicrograph of Transitional Epithelium (400X)
The shape of the cells next to the
lumen, the presence of scalloping,
and the fact that in the mucleus of
the cells next to the lumen the
nucleolus can be seen, are all
identification clues
CONNECTIVE TISSUE
The most abundant tissue type in the body. Most connective tissue has a rich blood supply (is
highly vascular). The exception to this rule is hyaline cartilage with is avascular. Connective
tissue is characterized by widely scattered cells found in an intercellular matrix.
The flow chart below illustrates the various types of connective tissue found in the human
body.
There are three basic elements found in connective tissue.
(1) Fibers (such as collagen, reticular, and elastic).
(2) Cells (such as fibroblasts, macrophages, and adipose).
(3) A ground substance (matrix).
All connective tissue (except cartilage) has an extensive nerve and blood supply.
The matrix (ground substance) of connective tissue may be:
(1) Fluid – as in Vascular Connective Tissue (blood).
(2) Semifluid – as in Loose Connective Tissue (Areolar).
(3) Gelatinous – as in Mucous Connective Tissue.
(4) Fibrous – as in Dense Regular Connective Tissue.
(5) Calcified – as Osseous Connective Tissue (bone).
Loose (Areolar) Connective Tissue (100X)
As the photomicrograph below illustrates this tissue has many collagen and elastic fibers.
The nuclei of many cells associated with connective tissue can be seen.
Description: Consists of collagen, elastic, and reticular fibers embedded in a semifluid
matrix, together with fibroblasts, mast cells, plasma cells and macrophages.
Location: Hypodermis (subcutaneous layer of skin), around most body organs.
Function: Loosely binds organs together
Photomicrograph of Loose (Areolar) Connective Tissue (100X)
******************************************************************************
Vascular Connective Tissue (Blood)
Blood is a connective tissue with a fluid matrix called plasma. Three basic types of cells are
found suspended in plasma:
(1) Erythrocytes (red blood cells).
Description: Biconcave cells that are stained pink. The thinner center of the cell is
lighter than the rim.
Location: Suspended in blood plasma.
Function: Transports respiratory gases (oxygen and carbon dioxide).
(2) Leukocytes (white blood cells) of which there are five basic types.
Description: Stained cells with an obvious (usually multi-lobed) nucleus.
Location: Suspended in blood plasma, also found in lymphatic tissues.
Function: Involved in immunity.
(3) Thrombocytes (or platelets) which are involved in blood clotting.
Description: Darkly stained structures much smaller than erythrocytes.
Location: Suspended in blood plasma.
Function: Involved in blood clotting.
Photomicrograph of Vascular Connective Tissue (400X)
The erythrocytes (red blood
cells) are pink with a light center
(where the cell is thinner and the
light shines through). The
Leukocytes (white blood cells) are
stained dark pink to purple and
have an obvious darkly stained
nucleus. The Thrombocytes
appear as small purple specks.
*************************************************************************
Adipose Connective Tissue (Fat)
As the photomicrograph below illustrates this tissue consists of adipocytes that wrap
themselves around lipid droplets.
Description: Resembles a chicken-wire fence. The individual adipocytes have a large central
storage area where fats and oils are stored.
Location: Subcutaneous layer of skin; fatty-capsule of the kidney, yellow bone marrow and
around the heart.
Function: Energy storage, insulation, protection.
Photomicrograph of Adipose Connective Tissue (100X)
This is a slide of the
hypodermis. Connective tissue
fibers, blood vessels, and sweat
glands can be seen embedded in
the adipose tissue
****************************************************************************
Dense Fibrous Connective Tissue (Regular)
This tissue contains of numerous collagen fibers oriented in the same direction. This
produces great strength in the direction that the fibers run.
Description: Many collagen fibers running in the same direction. Individual fibers appear
to be "wavy". Fibroblasts can be seen between the fibers.
Location: Makes up tendons and ligaments.
Function: Attaches muscles to bones (tendons) and bone to bone (ligaments).
Dense connective tissue has less flexibility than Areolar connective tissue but is more
resistant to stress. The collagen fibers are densely packed together, and run in one direction.
There is great strength in the direction of the fibers, but this tissue can be relatively weaker in a
direction at right angles to the fiber direction. The fibers and slightly crinkled allowing them to
stretch to some degree in the direction of the fibers.
Photomicrograph of Dense regular connective tissue (100X)
Note that the collagen fibers all run
in the same direction (on this view
from left to right). The "crinkly"
or "wavy" appearance of the fibers
is an identifiable characteristic of
this tissue.
******************************************************************************
Hyaline Cartilage Connective Tissue
This tissue has a matrix that is firm enough to bear a lot of pressure without permanent
distortion. Hence, it is found in joints where it functions as a shock-absorber and friction
reducing surface for bone articulation. Bones in the embryo start off as hyaline cartilage
templates for the later developing bone. This tissue is avascular and has no nerves.
Description: Consists of chrondrocytes (cartilage cells) located in spaces called lacuna,
surrounded by a bluish matrix interlaced with collagen fibers.
Location: Ends of long bones, between the ribs and the sternum, tracheal rings, parts of
the larynx, and embryonic skeleton.
Function: Reduces friction in joints, support with flexibility.
Photomicrograph of Hyaline Cartilage Connective Tissue (100X)
At this magnification to ring of
Hyaline Cartilage can be seen
occupying the center of the wall of
the trachea. The individual cells of
the cartilage (chondrocytes) are
just visible.
Photomicrograph of Hyaline Cartilage Connective Tissue (400X)
The chondrocytes in the lacuna
are obvious at this higher
magnification. Notice that the
chondrocytes often are found in
pairs inside the lacuna. The matrix
is blue to bluish-white.
****************************************************************************
Osseous Connective Tissue (bone)
The slide you will be looking at is a slice of dense bone from the shaft of a long bone, ground
down to become extremely thin and translucent (hence the slide name – "ground bone"). Bone
tissue has a hard matrix containing ions such as calcium and phosphorus. This matrix is laid
down around a dense network of collagen fibers in a layer called lamellae. System of canals
containing blood vessels, nerves and lumphatic vessels can be identified. They resemble tree
stumps and are known as Haversian systems or Osteons. Bone cells (Osteocytes) can be seen
inside their spaces (lacuna).
Description: A network of osteons makes ground bone resemble a field of tree stumps.
Location: Make up the bones of the body.
Function: Protection, support, mineral and fat storage (marrow). Together with skeletal
muscle is responsible for movement of the body.
Photomicrograph of Osseous Connective Tissue (100X)
The Haversian canal is located
in the center of the osteon. It
contains nerves, lymphatics and
blood vessels that run the length of
the bone. The wide opening on
the left is a Volkmann's canal that
transports the same structure from
the outside of the bone to the
inside of the bone (marrow cavity)
and back.
*****************************************************************************
MUSCLE TISSUE
Muscle tissue is composed of fibers that function to contract and short the muscle for
contraction. There are three distinct types of muscle tissue based on location, and structural
and/or functional characteristics.
Skeletal Muscle Tissue
Skeletal muscle tissue is so-called because it attaches to bones and is involved in the
movement of bones. It is also referred to as voluntary muscle because of the voluntary control of
its contraction, and/or striated muscle because of its striated appearance when you look at it
through a light microscope at high magnification.
Description: Long, striated fibers with the nuclei located at the edges of the fibers.
Location: Attached to bones by tendons.
Function: Moves bones, posture, heat production
Photomicrograph of Skeletal Muscle Tissue (400X)
Notice the striated appearance
of this tissue and the location of
the nuclei at the edge of the fiber
******************************************************************************
Smooth Muscle Tissue
Smooth muscle is composed of elongated cells that are not striated. Each smooth muscle cell
is largest at its midpoint and tapered towards its ends. Each cell has a single nucleus located in
the middle (or broadest) part of the cell.
Description: long tapered fibers with a centrally located nucleus.
Location: Walls of hollow internal organs such as the urinary bladder, stomach, intestines,
uterus, gall bladder, urinary bladder, blood vessels, and uterus.
Function: Movement of the substance inside the hollow organ (example: food in the
intestines, blood in the heart etc.).
Photomicrograph of Smooth Muscle Tissue (400X)
Notice the position of the single
nucleus in the center, broadest,
portion of the fiber. Notice also
that the fibers are nonstriated.
******************************************************************************
Cardiac Muscle Tissue
Cardiac muscle is composed of striated fibers that are bifurcated or branched. The nuclei are
centrally located. The presence of darkly stained intercalated discs is a good identification
characteristis.
Description: Branched striated fibers with a centrally located nucleus.
Location: Wall of the heart.
Function: Pumps blood to all parts of the body.
Photomicrograph of Cardiac Muscle Tissue (400X)
NERVOUS TISSUE
Two basic types of cells are found in nervous tissue. Neurons are large cells that function to
conduct impulses from one part of the nervous system to another (example: from the spinal cord
to the brain). Neuroglia are small cells that "glue" the neurons together (they have many other
functions as well).
Description: Large neuron cell bodies with obvious processes extending from them. Many
small nuclei of neuroglial cells (the neuroglial cells themselves cannot be seen.
Location: Nervous system.
Function: Conducts nerve impulse.
Nervous Tissue: Ox spinal cord (100X)
Notice the large cell body with
a conspicuous nucleus. The axon
and dendrite (cell processes) are
easily identified. The small nuclei
of neuroglial cells (astrocytes) are
evident.