VETERINARY HISTOLOGY
VMED 370
EPITHELIAL TISSUES
• There are (4) types of tissue:
GENERAL CHARACTERISTICS OF EPITHELIUM:
 Epithelial tissues are anchored to (sit on) a
basement membrane,
 They are made up of tightly packed cells
connected by intercellular junctions
 They are avascular -- generally lack blood vessels
 Regenerate – in case they are damaged –
meaning they are easily replaced.
All epithelial tissue sits on a basement membrane
Basement membrane:
a thin extracellular supporting layer that separates a layer of epithelial cells from the underlying lam
ina propria. It is composed of the basal lamina and reticular lamina is composed of Type IV
collagen, laminin, fibronectin, and proteoglycans such as heparan sulfate.
nucleus
Through intercellular junctions,
cells come together to form
tissues
LOCATION
Lining of body cavities and surfaces of visceral organs
– mesothelium
Lining of digestive tract, respiratory, urinary tract,
reproductive tract etc
Lining of heart, lymphatic vessels, and blood vessels
– endothelium
Lining of glands (endocrine + exocrine) and exocrine
gland ducts
Lining of the skin – epidermis
FUNCTION OF EPITHELIUM
• Protection – infection, toxic chemicals, UV
radiation (skin)
• Absorption – absorption of nutrients nourishes cells
and tissues; maintain homeastasis
• Secretions – hormones, mucus, enzymes
Classification of epithelial tissues:
Based on SHAPE:
• Squamous epithelium – thin, “flattened”
• Cuboidal epithelium – cubed shape
• Columnar epithelium – rectangular -- think
“column”
Based on SHAPE:
Squamous
Cuboidal
Columnar
How epithelial tissues are classified:
Based on number of cell LAYERS:
Simple epithelium = single layer
Stratified epithelium = more than one layer
Pseudostratified epithelium = one layer but
looks as if it has many layers
Simple epithelium
Pseudostratified
BM

One layer of cells


One layer of cells
Cells not the same height
Stratified epithelium
Basal surface

Two or more layer of cells
BM
Types of epithelium
• Simple squamous
• Stratified squamous
• Simple cuboidal
• Stratified cuboidal
• Simple columnar
• Stratified columnar
• Pseudostratified
Simple Squamous Epithelium
 Simple squamous epithelium is made up of a single
layer of thin, flattened cells.
 Because it is suited for diffusion, it has functions in
the exchange of gases in the lungs and lines blood
and lymph vessels as well as body cavities.
Figure 4.3a Epithelial tissues.
SIMPLE SQUAMOUS EPITHELIUM
(a) Simple squamous epithelium
Description: Single layer of flattened
cells with disc-shaped central nuclei
and sparse cytoplasm; the simplest
of the epithelia.
Air sacs of
lung tissue
Function: Allows passage of
materials by diffusion and filtration
in sites where protection is not
important; secretes lubricating
substances in serosae.
Nuclei of
squamous
epithelial
cells
Location: Kidney glomeruli; air sacs
of lungs; lining of heart, blood
vessels, and lymphatic vessels; lining
of ventral body cavity (serosae).
Photomicrograph: Simple squamous epithelium
forming part of the alveolar (air sac) walls (125x).
The Bowman’s capsule in the kidney is lined by a squamous epithelium. Note that the proximal and distal
convoluted tubules are instead lined by a simple cuboidal epithelium.
Endothelial cells are specialized squamous epithelial cells that line the
lumen of blood vessels, lymphatic vessels and heart
LYMPHATIC VESSEL
BLOOD CAPILLARY
On the surface of most thoracic and abdominal organs (eg lung, liver,
spleen), there is a specialized type of epithelium called mesothelium.
Mesothelium on the visceral pleura
Alveolar space
Alveolar space
A specialized type of simple squamous epithelium is found lining the body cavities and the
surfaces of most visceral organs eg. Lung, liver, spleen
SIMPLE CUBOIDAL EPITHELIUM
 Simple cuboidal epithelium consists of a single layer
of cube-shaped cells with centrally located nuclei.
 It functions in absorption eg. in the proximal
convoluted tubules of the kidneys
 It functions in secretion eg. in glands –

Endocrine glands eg thyroid gland;

Exocrine glands eg exocrine pancreas.
Figure 4.3b Epithelial tissues.
SIMPLE CUBOIDAL EPITHELIUM
(b) Simple cuboidal epithelium
Description: Single layer of
cubelike cells with large,
spherical central nuclei.
Simple
cuboidal
epithelial
cells
Function: Secretion and
absorption.
Basement
membrane
Location: Kidney tubules;
ducts and secretory portions
of small glands; ovary surface.
Connective
tissue
Photomicrograph: Simple cuboidal
epithelium in kidney tubules (430x).
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Simple Cuboidal
Simple cuboidal epithelium found in renal tubules
Simple cuboidal epithelium lining the surface of the ovary
Simple cuboidal epithelium on the front surface of the eye lens
Stratified cuboidal epithelial tissues are more rare comparing to other
epithelial types. This picture was taken from salivary gland duct
showed that the inner most layer, or right around the lumen, contains
cuboidal cells but the rest of the layers may or may not be cuboidal in
shape.
https://kitng.me/2016/08/03/stratified-cuboidal-epithelium/
Stratified cuboidal epithelium is rare and only found
in some glands and their ducts
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SIMPLE COLUMNAR EPITHELIUM
Made up of a row of elongated cells whose nuclei are all
located near the basement membrane. It may be ciliated
or bear microvilli.
It lines the uterus, stomach, and intestines where it
protects underlying tissues, secretes digestive fluids, and
absorbs nutrients.
In the intestine, these cells possess microvilli that
increase the surface area available for absorption.
Mucus-secreting goblet cells can be found among
columnar cells.
Figure 4.3c Epithelial tissues.
SIMPLE COLUMNAR EPITHELIUM
(c) Simple columnar epithelium
Description: Single layer of tall cells
with round to oval nuclei; some cells
bear cilia; layer may contain mucussecreting unicellular glands (goblet cells).
Simple
columnar
epithelial
cell
Function: Absorption; secretion of
mucus, enzymes, and other substances;
ciliated type propels mucus (or
reproductive cells) by ciliary action.
Location: Nonciliated type lines most of
the digestive tract (stomach to anal canal),
gallbladder, and excretory ducts of some
glands; ciliated variety lines small
bronchi, uterine tubes, and some regions
of the uterus.
Basement
membrane
Photomicrograph: Simple columnar epithelium
of the stomach mucosa (860X).
Simple columnar epithelium
Alcian blue stain
H&E
Simple columnar epithelium lining the surface of the simple stomach
The gall bladder is also lined by a simple
columnar epithelium
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STRATIFIED SQUAMOUS EPITHELIUM
This type of epithelial tissue is made up of layers of
flattened cells that are designed to protect underlying
tissues.
 It makes up the outer layer lining the:
– Epidermis of the skin; hooves
– Oral cavity (mouth),
– Oesophagus
– Vagina, and anal canal
– Rumen, reticulum, omasum (ruminant stomach)
Keratin layer
Epidermis
Dermis
In the skin, the keratinized squamous epithelium covers body surfaces thus
providing protection
In the skin, the keratinized squamous epithelium covers
body surfaces thus providing protection
In the oesophagus, a nonkeratinized stratified
squamous epithelium
covers the surface and
protects the underlying
tissues from noxious
insults.
Note that the cells in the
outer layers of the
oesophagus lack keratin.
The epithelium may
undergo keratinization in
case of some disease
conditions
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Keratinized squamous epithelium like that seen in the skin and
hooves of animals is quite effective in protecting underlying tissue
especially in areas exposed to the body surface
HOOF
SKIN
keratin
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F. Stratified Cuboidal Epithelium
1. This tissue consists of two to three layers
of cuboidal cells lining a lumen of the ducts of
mammary glands, sweat glands, salivary glands,
pancreas.
2. Several layers of cells provide greater
protection than one single layer.
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STRATIFIED CUBOIDAL
Stratified Epithelium
3. Stratified Cuboidal
–
Ducts of sweat glands -- this type + stratified columnar
are rare!
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PSEUDOSTRATIFIED COLUMNAR EPITHELIUM
1. These cells appear layered due to the varying
positions of their nuclei within the row of cells, but in
actual fact the cells are not truly layered.
2. Cilia may be present, along with mucus-secreting
goblet cells, that line and sweep debris from
respiratory tubes.
Figure 4.3d Epithelial tissues.
PSEUDOSTRATIFIED EPITHELIUM
(d) Pseudostratified columnar epithelium
Description: Single layer of cells of
differing heights, some not reaching
the free surface; nuclei seen at
different levels; may contain mucussecreting cells and bear cilia.
Cilia
Mucus of
mucous cell
Pseudostratified
epithelial
layer
Function: Secretion, particularly of
mucus; propulsion of mucus by
ciliary action.
Location: Nonciliated type in male’s
sperm-carrying ducts and ducts of
large glands; ciliated variety lines
the trachea, most of the upper
respiratory tract.
Trachea
Photomicrograph: Pseudostratified ciliated
columnar epithelium lining the human trachea (570x).
Basement
membrane
Pseudostratified epithelium in the bronchus. This is seen in the
respiratory epithelium of the nasal cavity, and trachea as well.
Pseudostratified epithelium is also seen in the epididymis. It has long cilia called stereocilia
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TRANSITIONAL EPITHELIUM
1. Transitional epithelium is designed to distend
and return to its normal size, as it does in the
lining of the urinary bladder.
2. This design provides distensibility and keeps
urine from diffusing back into the internal
cavity.
Also found in renal pelvis, ureter, proximal parts of
urethra
Transitional epithelium
Transitional epithelium
In addition to protection, the transitional epithelium found in the urinary bladder,
ureter, and renal pelvis can stretch and accomondate increasing amounts of urine.
CELL SURFACE MODIFICATIONS
 Microvilli – short fingerlike projections of the cell membrane
that increase surface area for absorption
 Cilia– projections of the cell membrane composed of microtubules (9 +1
pairs pattern)
 Common in the respiratory tract – adopted to move particles trapped in
mucus
 Stereocilia – long microvilli found in the epididymis and ear