02 Epithelial Tissue.pdf

Epithelial Tissue Epithelial tissue covers body surfaces and lines body cavities. It is made up of special cells that enable it to fulfill many functions-protection, secretion, excretion…  Respiratory Oral cavity Passages Skin Pleural cavities Digestive Tract...

Epithelial Tissue Epithelial tissue covers body surfaces and lines body cavities. It is made up of special cells that enable it to fulfill many functions-protection, secretion, excretion…  Respiratory Oral cavity Passages Skin Pleural cavities Digestive Tract Heart and Blood vessels Peritoneum Pericardium Urinary tracts Glands Limph vessels Characteristics of epithelial tissue:  composed of closely aggregated polyhedral cells  almost no/or no extracellular substance  epithelial cells are separated from the connective tissue by the basal lamina No blood vessels- nutrition from connective tissue!!! FUNCTIONS OF EPITHELIA COVERING EPITHELIA covering of surfaces and lining of cavities protection of covered tissue absorption - intestines, proximal tubules of kidney GLANDULAR EPITHELIA secretion - exocrine glands NEUROEPITHELIAL CELLS sensation - olfactory epithelium, taste buds BASAL LAMINA Selective barrier between connective tissue and epithelium Adhesion of the connective tissue and the epithelium Supporting the cells COMPONENTS OF BASAL LAMINA LAMINA LUCIDA (rara) Glycoproteins - laminin proteins – nidogen (entactin) Proteoglycans – perlekan LAMINA DENSA collagen type IV RETICULAR LAMINA collagen type III, small amount of collagen type I Anchoring fibrills – collagen type VII Basement membrane organization. Epithelial cells are linked to connective tissue via a network of matrix proteins. Laminin 5 connects integrins on the basal surface of epithelial cells to the type IV collagen network in the lamina densa of the basement membrane. Anchoring fibrils composed of type VII and type XV collagen link the basement membrane to the interstitial matrix where type I collagen, type III collagen and elastic fibers are found. Integrins located on the fibroblast cell surface interact with many matrix proteins including type I collagen. Copyright © 2003, 2007. Modified with permission from Dunsmore SE, Chambers RC, Laurent GJ. 2003. Matrix Proteins. Figure 2.1.2. In: Respiratory Medicine, 3rd ed. London. Saunders, p. 83; Dunsmore SE, Laurent GJ. 2007. Lung Connective Tissue. Figure 40.1. In: Chronic Obstructive Pulmonary Disease: A Practical Guide to Management, 1st ed. Oxford. Wiley-Blackwell, p. 467. POLARITY OF EPITHELIA APICAL SURFACE BASAL SURFACE - rests on basal lamina LATERAL SURFACE  TYPES OF EPITHELIA ACCORDING TO NUMBER OF LAYERS simple stratified pseudostratified ACCORDING TO SHAPE OF CELLS squamous cuboidal columnar  Clssification of Epithelia EPITHELIA simple Stratified squamous cuboidal columnar pseudostratified stratified transitional Stratified squamous Stratified columnar keratinized Non-keratinized THE SHAPE OF THE NUCLEUS THE SHAPE OF THE CELL!!! columnar  SIMPLE SQUAMOUS EPITHELIUM endothelium, mesothelium, air sacs of the lungs (alveoli) SIMPLE CUBOIDAL EPITHELIUM proximal and distal renal tubules  SIMPLE COLUMNAR EPITHELIUM stomach, small and large intestine, oviduct  PSEUDOSTRATIFIED EPITHELIUM respiratory passages, ductus epididymis STRATIFIED EPITHELIA STRATIFIED SQUAMOUS EPITHELIUM keratinized - skin nonkeratinized - oral cavity, vagina STRATIFIED CUBOIDAL EPITHELIUM TRANSITIONAL EPITHELIUM urinary bladder, ureter INTERCELLULAR JUNCTIONS membrane associated structures responsible for cohesion and communication between cells!!!  TIGHT JUNCTION – ZONULA OCCLUDENS LOCATION - the most apical SHAPE - band encircling the cell MORPHOLOGY - network of linear fusion sites between membrane associated proteins FUNCTION - close off the intercellular space In the cells, which the main function is absorption- urinary bladder, intestines  TIGHT JUNCTION - ZONULA OCCLUDENS Functions: Prevent Prevent the - Determination of the flow movement between of membrane epithelial cell polarity by the cells proteins separating the apical domain from the basolateral domain - Prevent the free pasage of substances between epithelial cells  Nectin JAM Occludin Claudin ZO 1,2,3 Afadin F Actin TIGHT JUNCTION - ZONULA OCCLUDENS  ZONULA ADHERENS Encircles the cell Just below the zonula occludens Insertion of actin filaments into electron-dense plaques of material on the cytoplasmic surfaces Glicoproteins –nectine and cadherin (between two cells) DESMOSOME - MACULA ADHERENS LOCATION - along the lateral membranes DISK-SHAPED MORPHOLOGY - attachment plaques - desmoplaquin intercellular space - desmoglein cytokeratin filaments FUNCTION - adhesion of neighbor-cells  HEMIDESMOSOME LOCATION - contact zone between epithelium and basal lamina DISK-SHAPED MORPHOLOGY - half a desmosome FUNCTION - binds the epithelial cell to basal lamina GAP JUNCTION -NEXUS LOCATION - anywhere along the lateral membranes of epithelial cells MORPHOLOGY - hexamers of proteins with a hydrophilic pore in the center (connexon) FUNCTION - interchange of small molecules between cells (ions) EPITHELIA SURFACES MODIFICATIONS  MICROVILLI Extension of cytoplasm - 1mm long Clusters of actin filaments FUNCTION - increase the surface area (absorbtive) LIGHT MICROSCOPE - BRUSH BORDER CILIA LONG PROJECTIONS - 10 mm MOTILE STRUCTURE: central pair of microtubules 9 pairs at the periphery FUNCTION – cilia enable to remove material over epithelium PRIMARY CILIARY DYSKINESIA (PCD) IMMOTILE CILIA SYNDROME STEREOCILIA – LONG MICROVILLI (IN EPIDIDYMIS AND DUCTUS DEFERENS) FLAGELLA - SIMILAR STRUCTURE TO CILIA GLYCOCALYX Function:  protection  antigenic character to the cell  enables the mutual recognition of cells (organogenesis) absorption of the substance on the cell surface BASAL STRIATIONS Renal tubules cells, parietal cells in stomach, salivary glands GLANDULAR EPITHELIA - GLANDS FUNCTION - secretion of products which are used in other parts of the organism  Glandular Epithelia Goblet cells stomach  TYPES OF EXOCRINE GLANDS HOLOCRINE APOCRINE secretory product is secretory product is shed with whole cell discharged with apical part of cytoplasm MEROCRINE secretory granules leave the cell by exocytosis (secretory vesicles) MEROCRINE secretory granules leave the cell by exocytosis (secretory vesicles) APOCRINE secretory product is discharged with apical part of cytoplasm HOLOCRINE secretory product is shed with whole cell  Glandular epithelia simple Unicellular glands branched compound tubule acini tubuloacini Mucous secretion placement of the duct Serous secretion Mix secretion  Glandular Epithelia Multicellular gland Sebaceous gland Proliferating layer SENSORY EPITHELIA NUTRITION OF EPITHELIA NO BLOOD VESSELS IN EPITHELIA NUTRIENTS AND PRECURSORS OF PRODUCTS DIFFUSE FROM CONNECTIVE TISSUE ACROSS THE BASAL LAMINA TO EPITHELIAL CELLS  Regeneration of epithelia Skin epithelium Proliferating cells Basal lamina Other kind of epithelia Among the epithelial cells there are stem cells which can divide throughout the whole life. The average cell life time - approx. 3 days in the epithelium of the intestine, 15-30 days in the epidermis,> 50 days pancreas   Modulation  the temporary change the structure and function of epithelial  Metaplasia  permanent change in the structure and function of epithelial cells in pathological conditions (smoking, chewing tobacco - oral epithelium, respiratory)  Epithelial cells may undergo malignant transformation. - Carcinoma - cancers derived from epithelia - Adenocarcinoma – cancerogenic transormation of the glandular epithelia