Anatomy

1. EPITHELIAL CELLS
• Cover the outer surface of body
• Line the luminal structure & body
cavities
Introduction

2. • Separated by little inter cellular space
• Usually avascular, nourishment – diffusion
from blood vessels in underlying tissues.
• Derived from all the 3 germ layers
• Cells rest on basement membrane
• It exhibits polarity, surface modifications
[cilia,microvilli,stereocilia]&good
regenerative capacity
Features

3. • The shape of epithelial cells is related to amount of
contained cytoplasm and organelles these in turn
related to metabolic activity.
• The contact between adjoining cells are by
specialized cell junction such as desmosomes.Some
epithelial cells contain pigment[ eg: skin , retina]
• The epithelial cells that look alike in shape could
have different functions
• Epithelial cells contain some proteins such as
cytokeratin.

4. Protection
The cells in epithelial tissue are very closely packed together
and joined with little space between them. For example, the
skin is composed of a layer of epithelial tissue (epidermis) that is
supported by a layer of connective tissue. It protects the
internal structures of the body from damage and dehydration.
Epithelial tissue also helps to protect against microorganisms.
The skin is the body's first line of defense against bacteria,
viruses, and other microbes.
Absorption
Epithelial tissue functions to absorb, secrete, and excrete
substances. In the intestines, this tissue absorbs nutrients during
digestion.
Functions

5. Secretion
Epithelial tissue in glands secrete hormones, enzymes,
and other substances. Epithelial tissue in the kidneys excrete
wastes, and in the sweat glands excrete perspiration.
Exchange/Transportation
The regulation and exchange of chemicals between the
underlying tissues and a body cavity
Sensing
Epithelial tissue also has a sensory function as it contains
sensory nerves in areas such as the skin, tongue, nose, and
ears.

6. Miscellaneous
Ciliated epithelial tissue can be found in areas such as the
female reproductive tract and the respiratory tract. Cilia are
hair-like protrusions that help propel substances, such as dust
particles or female gametes, in the proper direction.

7. Based on no. of layer of cell
• Simple – single layered epithelium
• Stratified – multi layered epithelium
• Pseudo stratified epithelium – single
layered but false appearance of
stratification
Classification

9. • Cells are flattened, height very much less than breadth
• Has thin layer of cytoplasm
• Nucleus form bulging on the cell surface
• Surface view –cells appear polygonal
• Tight junctions between the cells
• Helps in rapid transportation of substances
Eg – lining epithelium of alveoli of lung, heart (endocardium), blood
vessel (endothelium), lines the free surface of [serous
pericardium,pleura and peritoneum]- mesothelium, loop of henle[ in
renal tubule]
FUNCTION
It helps in rapid transport of substances, diffusion of gases and
filtration of fluids.
Simple Squamous Epithelium

10. Simple Squamous Epithelium

11. • Height of the cell similar to breadth of the cell
• Surface – polygonal , In section - appear cuboidal
• Nucleus – rounded & centrally placed
Eg – thyroid follicles, inner surface of lens, pigment
cells of retina, on the surface of ovary, in ducts of
many glands, cuboidal epithelium with prominent
brush border is seen proximal convoluted tubules of
kidneys.
FUNCTION
It is mainly concerned with secretory and absorptive
functions.
Simple Cuboidal Epithelium

12. Simple cuboidal epithelium

13. • Height of the cell very much greater than breadth
• Nucleus – vertically oval & located towards basement
membrane
• In vertical section – cells appear rectangular, surface view –
polygonal
• Goblet cells – unicellular mucus secreting cells present in
association with columnar cells (stomach)
• Eg for simple columnar epithelium are mucous membrane
of stomach and large intestine.
• Two types
Simple Columnar Epithelium

14. • In certain structures, cell surface bears
projection – CILIA
• Eg – lining epithelium of fallopian tube,
uterus, most of respiratory tract, ependyma
lining central canal of spinal cord and
ventricles of brain.
a. Ciliated Columnar Epithelium

15. • Columnar cells bear surface foldings- microvilli [finger like projection]
• When micro villi are regularly arranged - striated border
(small intestine)
• If microvilli are irregularly arranged – brush border (gall bladder)
FUNCTION
• Some columnar cells have secretory function[ stomach, intestine]
• Some columnar cells secrete enzymes
• In respiratory tract cilia move mucous accumulating in bronchi[
containing trapped dust particles] towards larynx. In uterine tube
movements of cilia help in passage of ova towards uterus
• Microvilli increase the surface area for absorption.
b. Columnar Epithelium with Microvilli

16. • Cells are single layered
• All cells rest on basement membrane
• But the cells are of different size & shape
• Tall cells have broad apical part & small cells
have broad base
• Nucleus present towards broader end, so
nuclei appear to be arranged in more layers –
giving impression of stratified epithelium
• Tall cells are secretory, basal cells are stem-
cells
Pseudo stratified Epithelium

17. Eg [location]-
Ciliated pseudo stratified columnar epithelium
is seen in trachea and in large bronchi
Non-ciliated is seen in ductus deferens[vas
deferens],some parts of male urethra
Pseudo stratified columnar epithelium with
stereo cilia[long microvilli] is seen in epididymis.

19. • Has more than one layer of cells
• Different types based on cells of
superficial layer
1. Stratified squamous epithelium
2. Stratified cuboidal epithelium
3. Stratified columnar epithelium
4. Transitional epithelium
Stratified Epithelium

20. • Made of many layers
• Basal layer is usually columnar
• Upon that lies 2-3 layers of cuboidal / polyhedral
cells
• Superficial most cells are flattened
• This arrangement protects against friction
FUNCTION
• It is protective in nature
• Keratin prevents dehydration of underlying tissue.
1. Stratified Squamous Epithelium

21. • Stratified squamous non
keratinised epithelium-
surface remains moist & superficial cells are living
and have nuclei
Eg – lining epithelium of oral cavity, oesophagus,
vagina etc.
• Stratified squamous keratinized
epithelium – surface remains dry, superficial
cells are dead & replaced by keratin,which forms a
non-living covering over epithelium. Eg – Epidermis
of skin
This epithelium is of two types

22. Stratified squamous non
keratinised epithelium
Stratified squamous
keratinised epithelium
Stratified squamous epithelium

23. 2. Stratified Cuboidal epithelium
• Made of 2 or more layers of cuboidal cells
• Eg – lining epithelium of ducts of sweat glands
3. Stratified columnar epithelium
• Made of 2 or more layers cells
• Deep layer – cuboidal
• Superficial – columnar
• Eg – pancreatic duct, duct of salivary glands.
FUNCTION
• It is protective in function
• It helps in conducting the secretion of glands.
Stratified Epithelium

24. • Multi layered with 2-4 cells thick
• Transitional between stratified squamous to
stratified
columnar epithelium
• Also called urothelium, since it lines the
calyces, ureter, urinary bladder & initial
segment of urethra, which are also its
location.
4. Transitional Epithelium

25. • Deepest layer – small columnar / cuboidal
cells (stem cells)
• Intermediate – contains pear shaped cells
• Superficial layer
–single/multinucleated large polyhedral cells,
–also called dome shaped or umbrella cells
–Highly stretchable cells become flattened
when urinary bladder is full
Layers

26. FUNCTION
The cells of transitional epithelium are firmly united
to one another by numerous desmosomes. Because
of these connections cells retain their relative position
when epithelium is stretched or relaxed.
The lipid layer of plasma membranes over epithelial
cells are embedded with special glycoproteins. These
glycoproteins make membrane impervious and
resistant to toxic effects of substances present in
urine and thus afford protection to adjacent tissues.

27. Basement Membrane of
Epithelium

28. • Thin, delicate membrane
• Made of proteins, mucuopolysaccharides and
fibres
• Well demonstrated by PAS stain EM shows
• Basal lamina (nearest to epithelial cells)
• Reticular lamina or fibro reticular lamina
(merges with surrounding connective tissue)
Basement Membrane

29. • Basal lamina is divisible into
– Lamina lucida – transparent & nearer to cell membrane
of epithelial cell
– Lamina densa – made of fibrils
• Functions
– Structural support- It provides adhesion on one side to
epithelial cells and on the other side to connective tissue
– Barrier to diffusion of molecules
– Regulates – proliferation & differentiation
– It may influence the regeneration of peripheral nerves
after injury.
Basement Membrane

30. Types Subtypes Examples Functions
Simple Squamous Alveoli of lung, endothelium,
mesothelium
Exchange (diffusion)
Cuboidal Thyroid follicle Secretion , protection
Columnar GIT, gall bladder Protection, secretion,
absorption & lubrication
Pseudo stratified Trachea , bronchi, nasal cavity Protection, secretion
Stratified Stratified sq.
keratinised
skin Protection
Stratified sq. non
keratinised
Oral cavity, oesophagus Protection
Stratified cuboidal Ducts of sweat glands Absorption, secretion
Stratified
columnar
Conjunctiva, pancreatic duct Protection, secretion &
absorption
Transitional Renal calyces, ureter, urinary bladder Protection, distensibility

31. • Metaplasia – transformation of one type of
epithelium to other – precancerous condition
• Eg –Barrett’s oesophagus–stratified squamous
epithelium – columnar epithelium
• Kartegeners syndrome
Applied Aspects