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Chapter 2
Epithelium
1.General feature:
1) contain more cells and less extracellular ground
substance
2) Polarisaton:
---free outer surface: face air or other things
---basal
surface:
face
underlying
CT,
havebasement membrane
3) Avascularity,but innervation:
---no blood vessels
---rich in nerve terminals
4) Having 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.
3.Covering epithelium:
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, cell border are interdigitate
/with flattened ellipsoid nucleus
---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:
one layer of cells, with same height and width(in
side view) and hexagonal outline in surface view.
spherical centrally-located nucleus
---distribution: /the renal tubule
/thyroid
/the some ducts of mang glands
---main function: covering and secretion
3)
simple columnar epi.:
---structural features:
one layer of
columnar cells,with basally
lacated ovoid nucleus
goblet cell: scattered, secreting granulesmucinogen 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
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
4. 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, proliferation
differentiation of epi.cell
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.
5. Glandular epi. and gland
glandular epi.: epi are specialized for
secretion
gland: organs composed mainly of
glandular epi.
1)classification:
•
exocrine gland: discharge the secretion
through a duct system
•
endocrine gland: release the secretion
directly into blood steam
2) 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
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
②
ducts:
---from simple squamous epi to simple
columnar or stratified epi.
---carry out the secretions
---secrete or absorb water and ions