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 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

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, nm 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 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: nm, electron-lucent --basal lamina: 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 and differentiation of epi.cell

② plasma membrane infolding(basal longitudinal striation): ---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: ① acinus(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 side- serous demilune

② ducts: ---from simple squamous epi to simple columnar or stratified epi. ---carry out the secretions ---secrete or absorb water and ions