Transcript structure
Chapter 2 Epithelial tissue Zhong jie Li （李仲杰） School of medicine, Zhejiang University [email protected] 1.General feature: 1) contain more cells and less extracellular ground substance 2) Polarity: ---free outer surface: face the surface of the body or the lumen of an organ or gland ---basal surface: attached underlying connective tissue 3) Avascularity, but innervation: Free (apical) Surface ---no blood vessels ---rich in nerve terminals 4) High regeneration capacity 5) Functions: protection secretion absorption sensory reception Basement Membrane 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. * germinal epithelia 3. Classification of covering epithelium: According to the number of layer and the shape of surface 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. Cell Layers Simple Stratified Cell shape • Free surface • basal surface • lateral surface 1) simple squamous epi: ---structural feature: /one layer flattened cells, cell border are interdigitate closely /with flattened ellipsoid nucleus ---Distribution: • mesothelium: the simple squamous epi. which line the inner surface of body cavities such as thoracic, abdominal cavities and pericardiac . • endothelium: the simple squamous epi. which line the inner surface of cardiovascular and lymph vessels. • other place: alveoli, parietal layers of renal capsule. ---function: a) transport of materials b) facilitates movement of viscera 1. 2. Nuclei (flat and parallel to the surface of the epithelium) Face to lumen 1 * The entire circulatory system is lined by a S. S. Epi. that is called endothelium. The major body cavities ( peritoneal, pleural, pericardial) are lined by S. S. epi that is called mesothelium. Mesotheliu m Mesothelium on abdominal cavity 2) simple cuboidal epi.: ---structural feature: • one layer of cells, with same height and width , hexagonal in shape. • 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-mucus striated border ：free surface of cells often bear microvilli-thin finger-like cellular protjections which form striated border. simple columnar epi goblet cell 4) pseudostratified ciliated columnar epi.: four types of cells ---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. ---distribution: inner surface of large duct of respiratory passages nasal trachea cilia bronchi The epithelium of trachea Basement membrane 1. Nuclei 2. Epithelium 3. Cilia 4. Lumen Pseudostratified ciliated columnar epithelium 5) stratified squamous epi.: ---structural features: • Multi-layer cells • 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 ---distributon: • non-keratinised: mouth, pharynx, oesophagus, urethra and vagina • keratinised: the surface of body, make up the skin non-karatinised Keratinization: a process by which the superficial cells die and become tough, hard squama. 6) transitional epithelium: • Multi-layer cells • Flexible qualities --- change the number of layers and shape of cells (empty state — distended state） in the contracted bladder in the distended bladder ---distribution: renal pelvis, ureters, urinary bladder, part of the urethra. Dome-shaped cells. 4. Epithelial specializations Sides of cells: --- Apical (free) --- Basal --- Lateral 1)Specializations of the apical surface • Cell coat: Glycocalyx--- glycoprotein containing coat • Microvilli • Stereocilia: very long microvilli (immotile) • Cilia ① microvilli: ---definition: delicate finger-liked projections of cellmembrane 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, thus aid in the processes of secretion and absorption. ---distribution: /striated border: intestinal epi. cell /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: ---definition: 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 of cilia ---function: beat in a rhythmical manner and produce a forward-moving wave ---distribution: epithelial cells of respiratory tract respiratory tract Difference between microvilli & cilia appearance Microvilli Small and short Cilia Big & long observation EM Surface Cell-membrane Axes Cytoplasm Microfilament Terminal web Increase surface area LM Cellmembrane Cytoplasm Microtubule Basal body Movement Basal portion Function 2) specializations of the lateral surface ---intercellular connection of adjacent cells: • non-special manner: the minute space and adherent molecules (glycoproteins, proteoglycans, cadherin) • Special manner: 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 20-30 nm, with • • • low electron-density filaments interdigitate attachment plaque Many tonofilaments are inserted into attachment plaque, each filament make a hairpin loop and then passes back into the cytoplasm ---function: firmly connection Pemphigus 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: electron-lucid central channel ---function: provide a ions and small molecules pathway between cells connexons junctional complex: 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 • PAS + • EM: two layers --basal lamina: 20-300 nm, electron-dense, thread-liked and amorphous ground substance, produced by epithelium Cell --reticular lamina: RT+ground substance, produced by CT ---function: • support, connection, fixation • semi-permeable membrane • induce the movement, proliferation and differentiation of epithelium cell ② plasma membrane infolding (basal longitudinal striation): ---definition: the infolding of cell-membrane with many mitochondria at the basal surface of epithelium 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. 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. 5. Glandular epithelium and gland (study yourself ) • • glandular epithelium: are specialized for secretion gland: organs composed mainly of glandular epiithelium 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: Simple gland compound alveolar gland compound tubulo-alveolar 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 Mucous acinus c. mixed acinus: two types of cells ---structure: • mucous acinus • with several serous cells attach on one sideserous demilune ② ducts: ---from simple squamous epithelium to simple columnar or stratified epithelium ---carry out the secretions ---secrete or absorb water and ions Thank you !