Epithelium is a tissue that consists of closely packed cells that form a continuous layer. It covers external surfaces of the body and internal cavities. There are two main types of epithelium - glandular epithelium which produces secretions or excretions, and covering epithelium which forms protective layers. Covering epithelium is classified based on cell layers (simple vs stratified), cell shape (squamous, cuboidal, columnar), and cellular modifications like cilia or microvilli. Epithelium serves functions like protection, secretion, absorption, excretion, and transport.

1. EPITHELIUM
Prepared by: Maryam Fida (o-1827)

2. ■ Fertilization Cell  zygote
■ Differentiation
■ All tissues consist of cells and variable
amount of extracellular matrix (intercellular
substance)  synthesized by tissue cells and
exported into extracellular space
■ Four categories of tissues:
– Epithelial
– Connective
– Muscle
– Nerve
■ All organs of body  made up of two or more
tissues (parenchyma & stoma)

3. epithelium
■ A collection of closely packed cells with very small amount of
intercellular space between the cells.
■ Epithelium is avascular
■ It is supported by variable amount of loose connective tissue
which contains blood vessels
■ Between the epithelium & connective tissue is a sheet called
basement membrane or basal lamina.
■ Oxygen and Nourishment  Diffusion from the capillaries
present in underlying connective tissue

4. ■ It consists of continuous sheets of cells
that cover exposed body surfaces. It also
lines internal cavities, such as those of the
digestive, respiratory, cardiovascular,
and genitourinary systems.
■ Epithelium covers the external and
internal surfaces of the body and forms
the parenchyma (functional part) of
various glands
■ Two main groups of epithelium are:
– Glandular epithelium
– Covering epithelium

5. Glandular epithelium
■ Some epithelial cells of the body are
specialized to produce substances
■ These substances are not used by cell
itself, but expelled to the extracellular
compartment
■ These are either:
– Secretions (sebaceous glands, pancreas &
salivary glands)
– Excretions (sweat glands)

6. Covering epithelium
■ Also called surface epithelium
■ It consist of one or more layers of cells
■ It may cover the external body surface or line the
tubular passages and cavities of the body
■ e.g
– Epidermis of skin
– Respiratory tract
– Digestive tract
– Urogenital tract
– Internal surface of heart, blood vessels
– Lining of body cavities (the pericardial, plural
& peritoneal cavities)

7. Classification of covering
epithelium
■ Based on cell layers
– Simple epithelium (consist of one cell layer)
– Stratified epithelium (consist of two or more
cell layers)
– Psedostratified epithelium (consist of single
layer but gives a false appearance of being
stratified)
– Transitional epithelium (distended)
■ Based on the shape of cell
– Squamous epithelium (flat)
– Cuboidal epithelium (cube-like)
– Columnar epithelium (long, column-shaped

10. ■ Based on cellular modifications: (usually in columnar epithelial
cells)
– Cilia  fine motile hairs
– Microvilli  finger like extensions of cell
– Mucus secreting (Goblet) columnar cells

11. Simple squamous epithelium
■ Single layer of thin flat cells
■ It can also be folded or rolled
into tube shape e.g: blood
vessels
■ It also form membranes within
the body e.g parietal
peritoneum membrane

12. ■ Major examples:
1. Endothelium which covers the internal surface of heart, blood
vessels and lymph vessels
2. Mesothelium  lines pericardial, pleural and peritoneal
cavities
3. The lining epithelium of the alveoli of the lung

13. Simple cuboidal epithelium
■ Single layer of closely packed
cuboidal cells
■ Either straight or rolled in to
tube shaped
■ Lines small excretory ducts of
exocrine glands (salivary glands,
pancreas etc)  perform
secretion & absorption
■ Urinary (renal) tubules 
perform absorption
■ Respiratory bronchioles lining

14. ■ The thyroid gland
■ In the eye, cells of pigmented
epithelium of the retina and epithelium
of the ciliary body are simple cuboidal
 these are specialized for ion
transport and secretion.

15. Simple columnar epithelium
■ Consist of single layer
of columnar (tall,
upright pillar) cells
■ This epithelium is
widely distributed in
the body
■ E.g. internal surface of
stomach, intestines,
gall bladder & uterus
■ In many locations in
body cells  it is
modified by cilia,
microvilli & goblet cells

16. ■ Simple columnar ciliated epithelium
– Make up lining of female’s fallopianTube
(oviduct)  cilia push the egg
■ Simple columnar epithelium with
goblet cells
– Makes up lining of stomach, MUCUS 
coat inside lining of stomach to protect it
from the action of HCL
■ Simple columnar epithelium with
microvilli & goblet cells
– Lines the intestine

17. Pseudostratified epithelium
■ A type of simple epithelium
■ Nuclei of the cells lie at different
levels  giving the epithelium a
false appearance of being stratified
■ Pseudostratified simple columnar
epithelium lines the conducting part
of respiratory system (nose,
nasopharynx, trachea & bronchi)
■ It also lines male genital ducts

18. Stratified (multilaminar)
epithelium
■ Classified according to shape of cells in superficial layer
■ STRATIFIED SQUAMOUS EPITHELIUM
■ STRATIFIEDCUBOIDAL EPITHELIUM
■ STRATIFIEDCOLUMNAR EPITHELIUM
■ A special type of stratified epithelium  TRANSITIONAL
EPITHELIUM

19. Stratified squamous epithelium
■ Lines surfaces subjected to
wear and tear
■ Numbers of layers vary, but
shape and arrangement is similar
■ Deepest/basal layer  by low
columnar or cuboidal cells (rapid
mitosis, cells progress from
base to surface)
■ At surface  cells are squamous

20. ■ There are two types of superficial (surface) cells
 keratinized & non-keratinized
■ STRATIFIED SQUAMOUS KERATINIZED
EPITHELIUM
– At surfaces which are subjected to abrasion &
drying  the cytoplasm of superficial cells
accumulate large numbers of keratin filaments
– Best example is the epidermis which covers the
entire free surface of the body
■ STRATIFIED SQUAMOUS NON-KERATINIZED
EPITHELIUM
– Lines surfaces which are subjected to abrasion but
remain wet
– Contains little or no keratin
– Examples include epithelium of most of the oral
cavity, oropharynx & esophagus

21. Stratified cuboidal epithelium
■ It consists of two or three
layers of cuboidal cells
■ Rarely distributed
throughout the body
■ Examples includes lining
of the ducts of some
exocrine glands like
pancreas, salivary glands
& sweat glands
■ Not involved in
absorptive or secretory
activity

22. Stratified columnar epithelium
■ Consists of columnar
surface cells resting on
one or more layers of
cuboidal cells
■ Rarely distributed
throughout body
■ Examples include lining
of conjunctiva of eye &
some parts of the male
urethra

23. ■ Unlike the stratified squamous
epithelium  the surface cells of
stratified cuboidal and stratified
columnar epithelium are not
continuously replaced by mitosis at
basal cell layer and no progress of cells
from the base to surface.

24. Transitional epithelium
■ A special type of stratified epithelium 
lines the urinary tract
■ Specially designed for stretch produced
by storing & passing of urine
■ It prevents reabsorption of urine
■ Lines renal calyces, renal pelvis,
ureters, urinary bladder & proximal
part of male & female urethra

25. BASEMENT MEMBRANE or BASAL
LAMINA
■ A thin layer of extracellular material present between epithelial
cells and the underlying connective tissue
■ It consist of:
– Collagen type IV
– Glycoproteins
■ Functions of basement membrane:
– Binds epithelial cells
– Provides support to epithelial cells
– Diffusion occurs through it  leading to
nourishment of epithelial cells

26. FUNCTIONS OF
EPITHELIUM
1. PROTECION
– Function of all
– Most marked in stratified squamous epithelium
2. SECRETION
– Goblet cells
3. ABSORPTION
– Lining of small intestine
– Epithelial cells of kidney tubules

27. 4. EXCRETION
– Urine & Sweat
5. TRANSPORT
– Cilia  transport of mucus & ovum

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