Chapter 2 Epithelium

1.General feature: 1.General feature: 1) contain more cells and less extracellular ground substance 2) Polarisaton: ---free outer surface: face the surface of the body or the lumen of an organ or gland ---free outer surface: face the surface of the body or the lumen of an organ or gland ---basal surface: face underlying connective tissue ---basal surface: face underlying connective tissue 3) Avascularity, but innervation: ---no blood vessels ---no blood vessels ---rich in nerve terminals ---rich in nerve terminals 4) Having functions of protection, secretion, 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.

3. Classification of covering epithelium : According to the number of layer and shape of cells According to the number of layer and shape of cells Simple epi.: ---simple squamous epi. ---simple cuboidal epi. ---simple cuboidal epi. ---simple columnar epi. ---simple columnar epi. ---pseudostratified ciliated columnar epi. ---pseudostratified ciliated columnar epi. Stratified epi.: ---stratified squamous epi. ---stratified columnar epi. ---stratified columnar epi. ---transitional epi. ---transitional epi.

1) simple squamous epi: ---structural feature: /one layer flattened cells, cell border are interdigitate closely /one layer flattened cells, cell border are interdigitate closely /with flattened ellipsoid nucleus /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. 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. endothelium: the simple squamous epi. which line the inner surface of cardiovascular and lymphatic system. other place: alveoli, parietal layers of renal capsule. other place: alveoli, parietal layers of renal capsule. ---function: a) transport of materials b) facilitates movement of viscera 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 in shape. one layer of cells, with same height and width, hexagonal in shape. spherical centrally-located nucleus spherical centrally-located nucleus

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

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

---distribution: gastrointestinal tract gall bladder gall bladder uterus uterus ---function: secretion and absorption goblet cell: scattered, secreting 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 membrane: Simple epi. four types of cells

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

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

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

6) transitional epithelium: flexible qualities flexible qualities -including the number of layers and shape of cells

---distribution: bladder

in the distended bladder: there are two to three layers of cells. The cells become flattened. in the distended bladder: there are two to three layers of cells. The cells become flattened. there are six to seven layers of cells. The surface cells are very large and cuboidal in shape, covering several deep cells. 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.

4. Epithelial specializations

1) Specializations of free surface

① microvilli: ① microvilli: ---definition: delicate finger-liked projections of cell- membrane and cytoplasm protruding from the free surface ---definition: delicate finger-liked projections of cell- membrane and cytoplasm protruding from the free surface

---structure: 0.1um in diameter, with different longth. 0.1um in diameter, with different longth. surface: cell membrane with cell coat surface: cell membrane with cell coat core: longitudinal microfilament-actin filament fixed on terminal web core: longitudinal microfilament-actin filament fixed on terminal web terminal web: made up of transverse-arranged filament at the apical side of cells terminal web: made up of transverse-arranged filament at the apical side of cells

---function: increase the surface areas, thus aid in the processes of secretion and absorption. ---distribution: /striated border: intestinal epi. cell /brush border: proximal renal tubule /brush border: proximal renal tubule Striated border

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

③ cilia: ③ cilia: ---definition: elongated, mobile projections of cell membrane and cytoplasm protruding from free surface

---structure: 5-10um long, nm in diameter 5-10um long, nm in diameter surface: cell membrane surface: cell membrane core: microtubules, 9X2+2 core: microtubules, 9X2+2 basal body: basal body: centrioles-connected with microtubules of cilia centrioles-connected with microtubules of cilia

---function: beat in a rhythmical manner and 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 manner: the minute space and adherent molecules (glycoproteins, proteoglycans) non-special manner: the minute space and adherent molecules (glycoproteins, proteoglycans) Special manner: junctional structures Special manner: junctional structures

① Tight junction (zonula occludens): ---structure: apical part apical part point-liked fused between adjacent point-liked fused between adjacent cells cells arranged in 2-4 thread-liked arranged in 2-4 thread-liked structures structures form anastomosing network form anastomosing network---function: seal the space between cells seal the space between cells

② intermediate junction (zonula adherens): ---structure: ---structure: below the tight junction below the tight junction a gap of 15-20nm in width with medium electron-density filament material 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 plaque of electron-dense materials, with attached microfilament-make up of terminal web ---function: ---function: /adherens /adherens /keep the cell shape /keep the cell shape /transfer cell contract force /transfer cell contract force

③ desmosome (macula adherens): ---structure: ---structure: plate or spot-shaped plate or spot-shaped a gap of nm, with a gap of nm, with low electron-density filaments interdigitate low electron-density filaments interdigitate Many tonofilaments are inserted into attachment plaque, each filament make a hairpin loop and then passes back into the cytoplasm Many tonofilaments are inserted into attachment plaque, each filament make a hairpin loop and then passes back into the cytoplasm ---function: ---function: firmly connection firmly connection

④ gap junction (communicating junction): ---structure: the smallest gap of 2-3 nm the smallest gap of 2-3 nm connexons: connexons: -consist of protein -consist of protein -7~9nm in diameter -7~9nm in diameter -composed of 6-subunits of proteins- connexin -composed of 6-subunits of proteins- connexin -2nm channel: electron-lucid central channel -2nm channel: electron-lucid central channel---function: provide a ions and small molecules pathway between cells provide a ions and small molecules pathway between cells

junctional complex: at least two types of junctional structures get together. at least two types of junctional structures get together.

3) specialization of basal surface

① basement membrane: ---definition: a sheet of membrane-liked amorphous material interposed between epithelium cells and underlying CT. ---structure: HE: pink colour, hard to see HE: pink colour, hard to see PAS + PAS +

EM: two layers EM: two layers -- basal lamina: nm, electron-dense, thread-liked and amorphous ground substance, produced by epithelium Cell -- basal lamina: nm, electron-dense, thread-liked and amorphous ground substance, produced by epithelium Cell --reticular lamina: RT+ground substance, produced by CT --reticular lamina: RT+ground substance, produced by CT

---function: support, connection, fixation support, connection, fixation semi-permeable membrane semi-permeable membrane induce the movement, proliferation and differentiation of epithelium cell induce the movement, proliferation and differentiation of epithelium cell

② plasma membrane infolding (basal longitudinal striation): (basal longitudinal striation): ---definition: the infolding of cell-membrane with many mitochondria at the basal surface of epithelium cell ---definition: the infolding of cell-membrane with many mitochondria at the basal surface of epithelium cell

---function: ---function: increase the basal surface areas increase the basal surface areas facilitate the passage of water and ions facilitate the passage of water and ions ---distribution: mainly in proximal and distal renal tubule. ---distribution: mainly in proximal and distal renal tubule.

③ hemidesmosomes ---is half of desmosome. ---is half of desmosome.

5. Glandular epithelium and gland glandular epithelium: are specialized for secretion glandular epithelium: are specialized for secretion gland: organs composed mainly of glandular epiithelium gland: organs composed mainly of glandular epiithelium

1)classification: exocrine gland: discharge the secretion through a duct system discharge the secretion through a duct system endocrine gland: release the secretion directly into blood steam release the secretion directly into blood steam

2) structure of exocrine gland: ① acinus (secreting unit): according the nature of secretion of secretion a. serous acinus: a. serous acinus: serous secretory cells serous secretory cells

Simple gland compound alveolar gland compound tubulo-alveolar gland Simple gland compound alveolar gland compound tubulo-alveolar gland

---structure: pyramid-shaped cell pyramid-shaped cell basally-located round nucleus basally-located round nucleus acidophilic cytoplasm-eosinophilic zymogen granules-contain enzymes acidophilic cytoplasm-eosinophilic zymogen granules-contain enzymes EM: RER, Golgi complex EM: RER, Golgi complex ---function: produce a serous secretion

b.mucous acinus: mucous secreting cells b.mucous acinus: mucous secreting cells---structure: pyramid-shaped cell pyramid-shaped cell flattened dark nucleus against the basal cell membrane flattened dark nucleus against the basal cell membrane slightly basophilic cytoplasm-large mucigen granules slightly basophilic cytoplasm-large mucigen granules EM: some RER, Golgi complex EM: some RER, Golgi complex ---function: secretes mucus

c. mixed acinus: two types of cells ---structure: ---structure: mucous acinus mucous acinus with several serous cells attach on one side- serous demilune with several serous cells attach on one side- serous demilune

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