Chapter 2 Epithelium

1.General feature: 1) contain more cells and less extracellular ground substance 2) Polarisation: ---free outer surface: face air or other things ---basal surface: have basement membrane, to face underlying CT, 3)  Avascularity, but innervation: ---no blood vessels ---rich in nerve terminals 4) Having functions of protection, secretion, absorption and sensory reception

2.Classification of Epithelium 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.

According to the number of layer and shape of cells 3. Classification of 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

Vascular endothelium

Mesothelium on abdominal cavity

2)      simple cuboidal epi.: ---structural feature: one layer of cells, with same height and width , hexagonal outline in surface view. spherical centrally-located nucleus

---distribution: /the renal tubule /thyroid /the some ducts of glands ---function: covering and secretion renal tubule thyroid

3)      simple columnar epi.: ---structural features: one layer of columnar cells, with basally located ovoid nucleus

---distribution: gastrointestinal tract gall bladder uterus ---function: secretion and absorption goblet cell: scattered, secreting granules-mucinogen granules-mucus goblet cell simple columnar epi

4) pseudostratified ciliated columnar epi.: ---Structural feature: 1, Four types of cells columnar cell (ciliated); goblet cell fusiform cell; basal cell:pyramid-shaped 2, Every cell locate on basement membrance: Simple epi. four types of cells

---distribution: inner surface of large duct of respiratory trachea bronchi nasal The epithelium of trachea

5) stratified squamous epi.: ---structural features: deepest (basal) cells: one layer of cuboidal cells the cells in intermediate regions: several layers of polygonal –shaped cells to the surface: more and more flattened cells

non-karatinised: mouth, pharynx, oesophagus, urethra and vagina ---distributon: non-karatinised: mouth, pharynx, oesophagus, urethra and vagina karatinised: the surface of body, make up the skin karatinised non-karatinised

6)      transitional epi.: 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

in the contracted bladder in the distended bladder

4. Epithelial specializations

1) Specialisations of free surface

     ①    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

② cell coat: ---defination: a thick layer of extracellular glycoprotein ---function: adherence, supporting, protection, exchange of material and recognize

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 basal body: centrioles-connected with microtubules

---function: swing to produce a forward-moving wave ---distribution: epithelial cells of respiratory tract 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

---structure: ③ desmosome (macula adherens): plate or spot-shaped a gap of 20-30 nm, with low electron-density filaments interdigitate attachment plaque: with attached tonofilament-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: --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

---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

increase the basal surface areas ---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

flattened dark nucleus against the basal cell membrane 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