H2T.pdf

General Histology lecture two: Epithelium Ahmed Abdul-Aziz Mohamed. PhD 1 Reference : Anthony L. MESCHER, Junqueira's Basic Histology TEXT & ATLAS  Epithelial tissue definition and Structure That type of tissue which lining inner and outer...

General Histology lecture two: Epithelium Ahmed Abdul-Aziz Mohamed. PhD 1 Reference : Anthony L. MESCHER, Junqueira's Basic Histology TEXT & ATLAS  Epithelial tissue definition and Structure That type of tissue which lining inner and outer body cavities, found in ecto, endo and mesoderm. The two basics structures of epithelial tissue are Basement membrane and Cell junctions Epithelial tissue is innervated, but avascular. This epithelial tissue must be nourished by substances diffusing from the blood vessels in the underlying tissue (basement membrane), but they don't have their own blood supply. 2  Epithelial tissue Structure Cell junctions are the contact points between plasma membrane and tissue cells. There are mainly 5 different types of cell junctions. They are tight junctions, adherents junctions, desmosomes, hemi-desmosomes, and gap junctions. 3  Functions of Epithelial Tissue 4  Classification of Epithelial Tissue 5 Epithelium Regeneration, Turnover, and Repair Turnover of both the epithelium in skin or oral mucosa occurs as a result of the cell division during the regeneration process. In order to migrate, the cells release and then regain their desmosomal connections at the intercellular junctions in the more superficial location. 6 Epithelium Regeneration, Turnover, and Repair The turnover time is faster epithelium, as compared to connective tissue due to higher level of mitosis in those deepest dividing cells near the basement membrane. The older, superficial epithelial cells are being shed or lost at the same rate as the deeper germinal cells are dividing into more cells during turnover time 7 Epithelium Regeneration, Turnover, and Repair The epithelium of the oral mucosa generally has a faster turnover time than the epidermis of the skin 8  Epithelium Regeneration, Turnover, and Repair The differences of turnover time are especially noted during repair or healing of the tissue after injury. Immediately after an injury to either the skin or oral mucosa, a clot from blood products forms in the area, and the inflammatory response is triggered by the white blood cells from the blood supply as they migrate into the tissue 9  Epithelium Regeneration, Turnover, and Repair Repair process of the skin or oral mucosa after an injury. Note the initial formation of the clot and migrating epithelial cells from the surrounding intact tissue and formation of granulation tissue in the later days of repair. Later, the tissue will remodel and form scar tissue. 10  Epithelium Regeneration, Turnover, and Repair The clot is very important in repair of the epithelium and must be retained in the first days of repair because it acts as a guide to form a new surface. The clot stays moist in the oral cavity but dries out on the skin (called a scab when on the skin). Later, after the epithelial surface is repaired, the clot is then broken down by enzymes because it is no longer needed for healing. Repair of the epithelium is a process that is also tied to repair in the deeper connective tissue. 11 Pemphigus vulgaris A blistering disease in which patients make autoantibodies to desmoglein proteins Epithelial cell connections (spot desmosomes) loosen, causing fluid accumulation and superficial blisters Bullous pemphigoid A blistering disease in which patients make autoantibodies to “bullous pemphigoid antigen” in hemidesmosome attachment plaques Epithelial cells detach from basal lamina, causing fluid accumulation and blister formation 14