Download 2-Epithelium

Epithelium
1.General feature:
1) contain more cells and less extracellular ground
substance
2) Polarization:
---free outer surface: face air or other things
---basal surface: face underlying CT, have
basement membrane
3) No vasa, but nerve:
---no blood vessels
---rich in nerve terminals
4) Functions of protection, secretion, absorption
excretion and sensory reception
2.Classification
1) Covering epithelium: the epithelium which cover
body surface or line the inner surface of body
cavities, tubes and sac.
2) Glandular epithelium: the epithelium which main
function is secretion.
3) Sensory epithelium: the epithelium which has
special sensory function.
Covering
epithelium
Where to find

Outer surface of the human body
Eg: epidermis of skin, cornea of eye

Inner surface of the canal, cavity or duct
Eg: respiratory tract, blood vessel，urinary duct
According to the number of layer and shape of
cells
Simple epi.: ---simple squamous epi.
---simple cuboidal epi.
---simple columnar epi.
---pseudostratified ciliated columnar epi.
Stratified epi.: ---stratified squamous epi.
---stratified columnar epi.
---transitional epi.
1)
simple squamous epi:
---structural feature:
/one layer flattened cells, unclear cell border
/with flattened or ellipsoid nucleus
/cell width > cell height (flattened)
---distribution:

mesothelium: the simple squamous epi. which
line the inner surface of body cavities such as
thoracic, pericardiac and abdominal cavities.

endothelium: the simple squamous epi.which
line the inner surface of cardiovascular and
lymphatic system.

other place: alveoli, parietal layers of renal
capsule.
---function: a) transport of materials
b) facilitates movement of viscera
2)
simple cuboidal epi.:
---structural feature:
 cell width = cell height (square)
 round centrally-located nucleus
---distribution: /the renal tubule
/thyroid
/the some ducts of male glands
---main function: covering and secretion
3)
simple columnar epi.:
---structural features:
 cell width < cell height (rectangle)
 basally located ovoid nucleus
 goblet cell: scattered, secreting
granules-mucinogen granules-mucus
---distribution: /gastrointestinal tract
/gall bladder
/uterus
---function: secretion and absorption
4)
pseudostratified ciliated columnar epi.:
---structural feature: four types of cells
/columnar cell:ciliated
/fusiform cell
/basal cell:pyramid-shaped
/goblet cell
---distribution: inner surface of large duct of respiratory
/trachea
/bronchi
/nasal
5)
stratified squamous epi.:
---structural features:

deepest(basal)cells: one layer of cuboidal cells

intermediate regions: several layers of
polygonal –shaped cells

to the surface: more and more flattened
---distributon:

non-karatinised:mouth,pharynx,
oesophagus, urethra and vagina

karatinised: the surface of body, make up
the skin
4
2
1
3
6)
transitional epi.:
---structural feature:

flexible-including the number of layers and shape of
cells

in the distended bladder: there are two to three
layers of cells. The cells become flattened.

in the contracted bladder : there are six to seven
layers of cells.
The surface cells are very large and cuboidal in shape,
covering several deep cells.
---distribution: bladder
Epithelial specializations
1)
Specialisations of free
surface
①
cell coat:
---defination: a thick layer of
extracellular glycoprotein
---function:
adherence,
supporting,
protection,
exchange of material and
recognize
②
microvilli:
---defination:
delicate
finger-liked projections
of cell-membrane and
cytoplasm protruding
from the free surface
---structure:
 0.1um in diameter, with different longth.
 surface: cell membrane with cell coat
 core: longitudinal microfilament-actin filament
fixed on terminal web
 terminal web: made up of transverse-arranged
filament at the apical side of cells
---function: increase the surface areas
---distribution: /striated border: intestinal epi.cell
/brush border: proximal renal tubule
③
cilia:
---defination: elongated, mobile projections of
cell membrane and cytoplasm protruding
from free surface
---structure:
 5-10um long, 300-500nm in diameter
 surface: cell membrane
 core: microtubules, 9X2+2, dynein
 basal body: centrioles-connected with microtubules
---function: swing to produce a forward-moving
wave
---distribution: epithelial cells of respiratory tract
2)
specializations of the lateral
surface
---intercellular connection of adjacent cells:

non-special: the minute space and
cadherin-cell adherent molecules

special: junctional structures
① Tight junction( zonula
occludens):
---structure:

apical part

point-liked fused between
adjacent cells

arranged in 2-4 thread-liked
structures

form anastomosing network
---function: seal the space
between cells
②
intermediate
junction(zonula adherens):
---structure:

below the tight junction

a gap of 15-20nm in width with
medium electron-density filament
material

plaque
of
electron-dense
materials,
with
attached
microfilament-make
up
of
terminal web
---function:
/adherens
/keep the cell shape
/transfer cell contract force
③
desmosome(macula
adherens):
---structure:
plate or spot-shaped

a gap of 20-30 nm, with low
electron-density
filaments
interdigitate
to
form
intermediate line

attachment plaque: with
attached tonofilament(10nm)intermediate filament(karatin)
---function: firmly connection

④ gap junction(communicating junction):
---structure:

the smallest gap of 2-3 nm

connexons:
-consist of protein
-7~9nm in diameter
-composed of 6-subunits of proteins- connexin
-2nm channel: hydrophilic channel
---function: provide a pathway between cells
*junctional complex: four
types of junctional
structures(at least two
types) get together.
3)
specialization of basal surface
①
basement membrane:
---defination: a sheet of membrane-liked
amorphous material interposed between
epi.cells and underlying CT.
---structure:
 HE: pink colour, hard to see
EM: three layers
--lamina lucida: 10-50 nm, electron-lucent
--basal lamina: 20-300 nm, electron-dense,
thread-liked
and
amorphous
ground
substance, produced by epi. Cell
--reticular lamina: RT+ground substance,
produced by CT
 glycoprotein: laminin, type IV collagen,
heparin sulfate proteoglycan and fibronectin

---function:
 support, connection, fixaton
 semi-premeable membrane
 induce
the movement,
differentiation of epi.cell
proliferation
and
②
plasma
membrane
longitudinal striation):
infolding(basal
---defination: the infolding of cell-membrane with
many mitochondria at the basal surface of epi.cell
---function:
 increase the basal surface areas
 facilitate the passage of water and ions
---distribution: mainly in proximal and distal renal
tubule.
③
hemidesmosomes
---is half of desmosome.
Gland


glandular epi.: epi are specialized for
secretion
gland: organs composed mainly of
glandular epi.
Classification of gland

According to the number of cell number:
Unicellular glands
multicellular glands
This is unicellular gland. There are some goblet cells
interspersed between the columnar cells.
This is multicellular gland. There are many special
glandular cells in groups.
According to the presence or absence
of ducts:
exocrine gland: discharge the secretion
through a duct system
• endocrine gland: release the secretion
directly into blood steam

1) structure of exocrine gland:
①acinus(secreting unit): according the nature of
secretion
a. serous acinus: serous secretory cells
---structure:

pyramid-shaped cell

basally-located round nucleus

acidophilic cytoplasm-eosinophilic zymogen
granules-contain enzymes

EM: RER,Golgi complex
---function: produce a serous secretion
2
2
1
b.
mucous acinus: mucous secreting cells
---structure:
 pyramid-shaped cell
 flattened dark nucleus against the basal cell
membrane
 slightly basophilic cytoplasm-large mucigen
granules
 EM: some RER, Golgi complex
---function: secretes mucus
c.
mixed acinus: two types of cells
---structure:
 mucous acinus
 with several serous cells attach on one sideserous demilune
demilune
②
ducts:
---from simple squamous epi to simple columnar
or stratified epi.
---carry out the secretions
---secrete or absorb water and ions




2) structure of endocrine gland:
Ductless gland
rich in network of blood capillaries or
sinusoid
arranged in cords, in clumps or follicles e.g.
thyroid gland
(see other chapters)