This document summarizes the key aspects of epithelium. It defines epithelium as a tissue composed of closely packed cells with little extracellular matrix. There are several types of epithelium that are classified based on the shape and layering of cells, including simple squamous, simple cuboidal, simple columnar, pseudostratified columnar, stratified squamous, stratified cuboidal, and stratified columnar epithelium. The document outlines the locations and functions of each type of epithelium, such as gas exchange, secretion, absorption, and protection of underlying tissues. Epithelial tissues are derived from all three germ layers and contain cell junctions that provide adhesion between cells.

1. Epithelium
H. M. Umair (2014)
Supervisor:
Dr. Pertab Rai.

2. o What is epithelium…..?
o Types of epithelium……!
o Locations……..!
o Functions…..!

3. Epithelium……
• (Epi) = upon; (Thelia) = nipple
• Epithelium is one of the four basic types of animal tissue.
• A collection of closely appose cells with very small amount
of extracellular matrix.
• Epithelial tissues are vascular, they never come in direct
contact with blood capillaries, so they must receive
nourishment via diffusion of substances from the underlying
connective tissue, through the basement membrane.
Connective tissue
Muscular tissue
Nervous tissue
Epithelial tissue

4. BASEMENT MEMBRANE
• Basement Membrane anchors epithelial cells to
underlying connective tissue

5. 1. Laminin
2. Type IV
collagen
3. Entactin
(Nidogen)
4.
Proteoglycans
BASAL LAMINA
visible in EM
20-100 nm thick
consists of dense and clear
layers
composed of macromolecules

6. Origin of epithelium
o Epithelial tissues are derived from all of the embryological germ layers:
from ectoderm (e.g., the epidermis);
from endoderm (e.g., the lining of the gastrointestinal tract);
from mesoderm (e.g., the inner linings of body cavities)

7. Simple
Squamous
Cuboidal
Pseudostrat
ified
Columnar stratified
Squamous
Columnar
Transitiona
l
Cuboidal
epithelium
Types.

8. Transitional epithelial
Dig. Of different Types.

9. Simple Squamous Epithelium
• Structure

10. Simple squamous epithelial tissue
lungs
Simple squamous epithelial tissue (superior view)

11. simple squamous; which is found lining areas where
passive diffusion of gases occur.
e.g. walls of capillaries,
linings of the pericardial,
pleural,
and peritoneal cavities,
as well as the linings of the alveoli of the lungs.
Locations….

12. Simple cuboidal epithelial tissue
Kidneys (tubules)

13. simple cuboidal: these cells may have secretory,
absorptive, or excretory functions.
e.g include small collecting ducts of
kidney
,pancreas
and salivary gland
Locations…

14. Simple columnar epithelial tissue

15. simple columnar; found in areas with extremely high secretive (as
in wall of the stomach), or absorptive (as in small intestine) areas.
they possess cellular extensions (e.g. microvilli in the small
intestine, or cilia found almost exclusively in the female
reproductive tract)
Locations…

16. Pseudostratified (ciliated) columnar epithelial tissue
trachea lining
“false layered”; it looks like more than one layer,
but it is not

17. pseudostratified epithelia; they are also called
respiratory epithelium.
this is due to their almost exclusive confinement to
the larger respiratory airways
i.e. the nasal cavity,
trachea,
bronchi e.t.c
Locations…

18. Stratified squamous epithelial tissue
mouth lining

19. Stratified squamous epithelial tissue
Keratinized :
In this particular case, the most apical layers (exterior) of cells are dead and lose
their nucleus and cytoplasm, instead contain a tough, resistant protein called keratin. This
specialization makes the epithelium waterproof, so is found in the mammalian skin
non-keratinized :
The surface cell become very flat and remain nucleated and
their cytoplasm contains little or no keratin……
The lining of the esophagus is an example of a non-keratinized or "moist" stratified
epithelium.

20. Locations…

21. Stratified cuboidal epithelial tissue
salivary glands, sweat glands

22. Locations…

23. Stratified columnar epithelial tissue
male reproductive tract

24. Locations…

25. Transitional epithelial tissue
empty bladder

26. Locations…

27. Functions….
• to protect the tissues that lie beneath it from radiation, desiccation, toxins,
invasion by pathogens, and physical trau.
• the regulation and exchange of chemicals between the underlying tissues and
a body cavity.
• the secretion of hormones into the blood vascular system, and/or the secretion of
sweat, mucus, enzymes, and other products that are delivered by ducts.
• to provide sensation.

28. Cell junctions are especially abundant in epithelial tissues. They consist of protein
complexes and provide contact between neighboring cells, between a cell and the
extracellular matrix, or they build up the paracellular barrier of epithelia and
control the paracellular transport.
Cell junctions…
Cell junctions are the contact points between
plasma membrane and tissue cells. There are
mainly 5 different types of cell junctions: tight
junctions, adherens junctions, desmosomes,
hemidesmosomes, and gap junctions. Tight
junctions are a pair of trans-membrane protein
fused on outer plasma membrane. Adherens
junctions are a plaque (protein layer on the inside
plasma membrane) which attaches both cells'
microfilaments. Desmosomes attach to the
microfilaments of cytoskeleton made up of
keratin protein. Hemidesmosomes resemble
desmosomes on a section. They are made up of
the integrin (a transmembrane protein) instead of
cadherin. They attach the epithelial cell to the
basement membrane. Gap junctions connect the
cytoplasm of two cells and are made up of
proteins called connexins (six of which come
together to make a connexon).

29. Thanks…
Doctors
A Q