4. WHAT ARE EPITHELIA
• single or multiple layers of cells
characterized by
• a layer or layers composed of closely
aggregated, polyhedral cells
• one side of cell layer(s) has a free
surface
• little intercellular substance between
cells
• cells cohere (stick) strongly to each other
• cells form a sheet that covers a surface
5. DEFINITION OF EPITHELIUM
Epithelium is an avascular tissue composed
of cells that cover
• the exterior body surfaces and
• lines internal body cavities and body
tubes that communicate with exterior
• Forms secretory portion of glands and
ducts
• Fuctions as receptors for special senses
9. CELLS FORMING EPITHELIUM
WIDTH OF
CELL IS
GREATER
THAN HEIGHT
WIDTH DEPTH
AND HEIGHT
ARE SAME
HEIGHT OF
CELL EXCEEDS
WIDTH
10. • Shape of cells forming surface layer is
used in classifying
epitheliumExamlpe:stratified
squmamous epithelium
• Specialization of apical cell surface
domains also used in classification
• Example :simple columnar ciliated
12. • ENDOTHELIUM: epithelial lining of
vascular system
• MESOTHELIUM:epithelium lining walls of
closed cavity.eg.,abdominal,pleural and
pericardial cavity
• Both are simple squamous epithelium
• Exception is postcapillary venules of
lymphatics having simple cuboidal
epithelium
13. FUNCTION OF EPITHELIAL TISSUE
Protection
• Skin protects from sunlight , bacteria & physical
damage.
Absorption
• Lining of small intestine, absorbing nutrients
into blood.
Filtration
• Lining of Kidney tubules filtering wastes from
blood plasma.
14. Secretion
• Different glands produce perspiration,
oil, digestive enzymes and mucus.
Transport
• Transport of materials along the
surface of epithelium by motile cilia.
Receptor function
• Taste buds of tongue,olfactory
epithelium of nasal mucosa
16. PSEUDODTRATIFIED COLUMNAR
EPITHELIUM
• Single layer of cells of differing heights, some not
reaching the free surface; nuclei seen at different
levels; may contain mucus-secreting cells and bear
cilia.
• Secretion, particularly of mucus; propulsion of mucus
by ciliary action.
• Trachea and bronchial tree
• Ductus deferens
• Efferent ductules of epidydimus
20. STRATIFIED SQUAMOUS EPITHELIUM
• Thick membrane composed of several cell layers;basal
cells are cuboidal or columnar and metabolically active;
• Polygonal layer lies next to it
• surface cells are flattened (squamous); in the
keratinized type, the surface cells are full of keratin and
dead; basal cells are active in mitosis and produce the
cells of the more superficial layers.
• Protects underlying tissues in areas subjected to
abrasion
• Epidermis, oral cavity,osophagus,vagina
25. Dysplasia
• refer to an abnormality of development or an
epithelial anomaly of growth and differentiation.
• Dysplasia is characterised by four major pathological
microscopic changes:
• Anisocytosis (cells of unequal size)
• Poikilocytosis (abnormally shaped cells)
• Hyperchromatism (excessive pigmentation)
• Presence of mitotic figures
30. TRANSITIONAL EPITHELIUM
• Many layers
• Very specialized – cells at base are cuboidal or
columnar, at surface large dome-shaped cells
• Change between stratified & simple as tissue is
stretched out.
• Allows stretching (distensible property)
• BARRIER functions
• Renal calyces, renal pelvis Urinary bladder, ureters &
urethra
33. • Cells in the basal layer are not much affected by
distention but the cells in next three or four layers
become flatenned.
• Large highly convex cells not only flatten but also
unfold to expose their luminal plasma membranes to
accommodate the increasing area.
• When fully streatched the apical plasmalemma of
most superficial cells of transitional epithelium
contain thick and rigid areas called plaques
34. • Between the plaques are present interplaque regions
consisting of normal flexible cell membrane.
• Microfilaments are seen to be extending from inner
surface of plaques to cytoplasm of cell
• In the relaxed bladder when plasma membrane is
folded these plaques invaginate into the cytoplasm
and are temporarily stored as fusiform vesicle. The
lumina of tehse vesicles remain in continuity with the
exterior of cell.
35. • As the bladder undergo distention the stored plaques
unfold and re emerge on the cell surface.
• Microfilaments attached to plaques provide structural
support during folding and unfolding process.
37. EPITHELOID TISSUE
• Epithelial cells which lack free surface but
do have basement membrane and close
opposition of cells
• In endocrine glands
• Lydig cells
• Islands of langerhans
• Accumulation of macrophages after
injury
