Chapter 2 Epithelium

1.General feature: 1) contain more cells and less extracellular ground substance 2) Polarisaton: ---free surface: face air or other things ---basal surface: have basement membrane, to face underlying connective tissue (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, e.g. 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 terminal web

cilia Tight junction desmosome intermediate junction

---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

connexons

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

Under EM: --basal lamina: 20-300 nm, electron-dense, thread-liked and amorphous ground substance, produced by epi. cell --reticular lamina: reticular tissue + ground substance, produced by CT

---function: support, connection, fixation 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 renal tubule 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 serous demilune

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

√ Multichosen question 1.The lining epithelium of the serous body cavities (pericardial, pleural and peritoneal) is endothelium mesothelium simple cuboidal epithelium stratified squamous epithelium transitional epithelium √

√ 2. An endocrine gland passes its secretion directly into the blood or lymph duct body surface digestive tract lumen of acinus √

3. The nucleus is flattened against the basal plasma memberane of the cells, the cytoplasm is filled with large mucigen droplets, it is the serous cell mucous cell serous demilune goblet cell myoepithelial cell √

Fill in the blanks Hematoxylin Eosin In H.E. stain sections, the cytoplasm is stained pink by ___________, the nucleus is stained purple-blue by___________________________. Hematoxylin Eosin

The procedure of preparation of histologic slides includes mainly______________________, ___________,_________________, _____________, ______________,and sectioning. Obtaining the specimen Fixation Dehydration Clearing Embedding

The 4 basic types of tissue are ______________,_________________,_________________ and _________________. epithelium connective tissue muscular tissue nervous tissue

Epithelia are mainly classified into 2 groups: ______________and_______________. Simple epi. Stratified epi

The intercellular junctions of epithelial cells are (1) _______________, (2) ___________________, (3) _____________, and (4)______________. When 2 or more kinds of them are present together, we called it __________________. Tight junction Intermediate junction Desmosome Gap junction Junctional complex

7. Specialized structures on basal surface of epithelial cells are ________________________________,_____________________________ and ______________________. basement membrane plasma membrane infolding hemidesmosomes

8. Pseudostratified columnar ciliated epithelium consists of 4 kinds of cells with different shape and height, but all set on the basal membrane: ________________________, ________________,_____________and ________________. columnar cell (ciliated) goblet cell fusiform cell basal cell

Questions Describe the characteristics of epithelial tissue. Describe the structural characteristics and functions of each covering epithelial type. Compare the structure of microvilli with cilia. Compare the structure of intermediate junction with desmosome.