Epithelial Tissue 2 PDF

Epithelial
tissue 2 Dr. Elriah.M.Maki
B.Sc , MBBS , M.Sc PhD  Objectives By the end of this session the student should be able to: Describe the Cell surface specializations Describe the classification of Glandular Epithelium and its features Cell surface specializations o Epithel...

Epithelial
tissue 2 Dr. Elriah.M.Maki
B.Sc , MBBS , M.Sc PhD  Objectives By the end of this session the student should be able to: Describe the Cell surface specializations Describe the classification of Glandular Epithelium and its features Cell surface specializations o Epithelial cells have many surface modifications and specializations related to their different functionalities. o These specializations occur at all the cell surfaces (apical, lateral and basal surfaces). Apical specializations o Microvilli. o Cilia. o Flagella. o Cell coat (Glycocalyx). Microvilli o Are small finger-like processes projecting from the free surface of the cell into the lumen. o They increase the surface area of the cell to increase its absorption Cilia o Are long motile hair-like processes projecting from the free surface of the cell into the lumen. o Cilia propel the mucus and other structure over the surface of the epithelium by rapid rhythmic oscillations. Flagella oAre similar to cilia, but single and very long. oPresent only in the spermatozoa. Glycocalyx oGlycoprotein attached to the external surface of the cell membrane. oFormed of carbohydrate chain attached to the transmembrane protein of the plasma membrane. Lateral specializations o Occluding (tight) junction. o Adhering junction. o Desmosome. o Gab junction. Tight Junctions o Located between the adjacent plasma membranes. o Are the most apically located junction. o Its function to prevent membrane proteins and water-soluble molecules from passing between the cells. Adhering Junctions o It is a junctional complex that lies just basal to the tight junction. o Function is not only joins the two cell membranes to each other, but also links the cytoskeleton of both cells. Desmosomes o Are weld-like junctions that help to resist the shearing forces. o Intermediate filaments are responsible for dispersing the shearing forces on the cell. Gap Junctions o Present in epithelial cells, cardiac and smooth muscles and neurons. o They are pores communicating between two adjacent cells and permit the passage of ions, amino acids and certain hormones between the cells. Glandular Epithelium Glandular epithelia are formed by cells specialized to produce secretion. The molecules to be secreted are generally stored in the cells in small membrane- bound vesicles called secretory granules. o The parenchyma represents the secretory units and the duct system, while stroma is the connective tissue between the parenchyma. Glandular Epithelium  Glandular epithelial cells may synthesize, store, and secrete proteins ( pancreas), lipids ( adrenal, sebaceous glands), or complexes of carbohydrates and proteins (salivary glands).  The mammary glands secrete all three substances.  Less common are the cells of glands that have low synthesizing activity like sweat glands Classification o There are many ways for classification of glands according to mode of secretion, type of secretion, way of secretion, number of secretory cells, duct system and shape of the secretory units. According to presence of ducts o Exocrine gland: means it pours its secretion through duct system to a particular place, e.g. salivary glands. o Endocrine gland: has no ducts and it delivers its secretion directly to the blood stream, e.g. thyroid gland. o Mixed gland: has both types, e.g. pancreas. According to mode of secretion o Holocrine gland: The whole cell is destroyed and detached, e.g. sebaceous gland. o Merocrine gland: The cell is intact and it secretes through exocytosis of secretory vesicles, e.g. salivary glands. o Apocrine gland: the apical part of the cell is detached, e.g. mammary gland. According to number of cells o Unicellular gland: one cell only, e.g. goblet cells in the epithelium of mucosa of respiratory tracts and intestine. o Multicellular gland: Many cells and they pour their secretion into the duct system, e.g. salivary glands. Thanks