Epithelium. 1.General feature: 1) contain more cells and less extracellular ground substance 2)...
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Epithelium
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1.General feature:1) contain more cells and less extracellular ground
substance2) Polarization: ---free outer surface: face air or other things ---basal surface: face underlying CT, have basem
ent membrane3) No vasa, but nerve: ---no blood vessels ---rich in nerve terminals4) Functions of protection, secretion, absorption e
xcretion and sensory reception
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2.Classification1) 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.
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Covering epithelium
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Where to find
Outer surface of the human body
Inner surface of the canal, cavity or duct
Eg: epidermis of skin, cornea of eye
Eg: respiratory tract, blood vessel, urinary duct
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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.
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1) simple squamous epi:
---structural feature: /one layer flattened cells, unclear cell border /with flattened or ellipsoid nucleus /cell width > cell height (flattened)
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---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
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2) simple cuboidal epi.:
---structural feature: cell width = cell height (square) round centrally-located nucleus
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---distribution: /the renal tubule
/thyroid
/the some ducts of male glands
---main function: covering and secretion
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3) simple columnar epi.:
---structural features: cell width < cell height (rectangle) basally located ovoid nucleus goblet cell: scattered, secreting granules-mucinogen granules-mucus
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---distribution: /gastrointestinal tract
/gall bladder
/uterus
---function: secretion and absorption
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4) pseudostratified ciliated columnar epi.:
---structural feature: four types of cells /columnar cell:ciliated /fusiform cell /basal cell:pyramid-shaped /goblet cell
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---distribution: inner surface of large duct of respiratory
/trachea
/bronchi
/nasal
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5) stratified squamous epi.:
---structural features: deepest(basal)cells: one layer of cuboidal cells intermediate regions: several layers of polygon
al –shaped cells to the surface: more and more flattened
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---distributon: non-karatinised:mouth,pharynx, oesophag
us, urethra and vagina karatinised: the surface of body, make up t
he skin
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1
2
3
4
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6) transitional epi.: ---structural feature: flexible-including the number of layers and shape of
cells in the distended bladder: there are two to three layer
s of cells. The cells become flattened. in the contracted bladder : there are six to seven lay
ers of cells. The surface cells are very large and cuboidal in shape,
covering several deep cells.---distribution: bladder
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Epithelial specializations
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1) Specialisations of free surface
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① cell coat: ---defination: a thick layer of ext
racellular glycoprotein
---function: adherence, supporting, protection, exchange of material and recognize
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② microvilli: ---defination: delicate fin
ger-liked projections of cell-membrane and cytoplasm protruding from the free surface
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---structure: 0.1um in diameter, with different longth. surface: cell membrane with cell coat core: longitudinal microfilament-actin filament fix
ed on terminal web terminal web: made up of transverse-arranged fila
ment at the apical side of cells
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---function: increase the surface areas
---distribution: /striated border: intestinal epi.cell
/brush border: proximal renal tubule
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③ cilia:---defination: elongated, mobile projections of c
ell membrane and cytoplasm protruding from free surface
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---structure: 5-10um long, 300-500nm in diameter surface: cell membrane core: microtubules, 9X2+2, dynein basal body: centrioles-connected with microtubules
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---function: swing to produce a forward-moving wave
---distribution: epithelial cells of respiratory tract
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2) specializations of the lateral surface
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---intercellular connection of adjacent cells: non-special: the minute space and cadheri
n-cell adherent molecules special: junctional structures
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① Tight junction( zonula occludens):
---structure: apical part point-liked fused between a
djacent cells arranged in 2-4 thread-liked
structures form anastomosing network
---function: seal the space between cells
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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
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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
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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
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*junctional complex: four types of junctional structures(at least two types) get together.
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3) specialization of basal surface
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① basement membrane:---defination: a sheet of membrane-liked amorph
ous material interposed between epi.cells and underlying CT.
---structure: HE: pink colour, hard to see
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EM: three layers --lamina lucida: 10-50 nm, electron-lucent --basal lamina: 20-300 nm, electron-dense, thr
ead-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
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---function: support, connection, fixaton semi-premeable membrane induce the movement, proliferation and differenti
ation of epi.cell
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② plasma membrane infolding(basal longitudinal striation):
---defination: the infolding of cell-membrane with many mitochondria at the basal surface of epi.cell
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---function: increase the basal surface areas facilitate the passage of water and ions
---distribution: mainly in proximal and distal renal tubule.
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③ hemidesmosomes
---is half of desmosome.
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Gland
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glandular epi.: epi are specialized for secretion
gland: organs composed mainly of glandular epi.
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Classification of gland According to the number of cell number:
Unicellular glands
multicellular glands
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This is unicellular gland. There are some goblet cells interspersed between the columnar cells.
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This is multicellular gland. There are many special glandular cells in groups.
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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
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1) structure of exocrine gland:
①acinus(secreting unit): according the nature of secretion
a. serous acinus: serous secretory cells
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---structure: pyramid-shaped cell basally-located round nucleus acidophilic cytoplasm-eosinophilic zymogen
granules-contain enzymes EM: RER,Golgi complex ---function: produce a serous secretion
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1
2
2
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b. mucous acinus: mucous secreting cells
---structure: pyramid-shaped cell flattened dark nucleus against the basal cell
membrane slightly basophilic cytoplasm-large mucigen g
ranules EM: some RER, Golgi complex
---function: secretes mucus
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c. mixed acinus: two types of cells ---structure: mucous acinus with several serous cells attach on one side- serous demilune
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demilune
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② ducts:
---from simple squamous epi to simple columnar or stratified epi.
---carry out the secretions
---secrete or absorb water and ions
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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)