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1BODY TISSUES and HISTOLOGYTissue TypesRequired Reading: Table 5.1 p 144Tissues are groups of cells with similar structure and function.There are four major types:1. Epithelial tissue2.Connective tissue3.Nervous tissue4.Muscular tissueEPITHELIUMSpecial Characteristics of Epithelial Tissue1.Cellularity:cells are usually packed together forming continuous sheets with very littleextracellular space or fluid in between. Adjacent cells are bound together at many points by celljunctions such as desmosomes or tight junctions.2.Polarity:epithelium has two surfaces; theapicalsurface is exposed to either the exterior of thebody or a cavity.It may contain modifications such as cilia or microvilli.Thebasalsurface onthe other hand is the deepest surface which rests on a basement membrane.3.Connective tissue support:all epithelial cells rest on a membrane calledbasement membrane.The basement membrane consists of two layers.Just beneath the cells is thebasal lamina,which is primarily made of protein secreted by the cells.Beneath the basal lamina is areticularlaminaof connective tissue.4.Avascular:Has no blood supply of its own, but receives its nourishment from underlyingconnective tissues which are richly vascularized.It has nerve supply.5.Regenerative: When properly nourished, the layer closest to connective tissue has the capacityto regenerate by mitosis.Location ofEpithelial Tissue1.Body coverings (surface of body)2.Body lining (of the internal cavities)3.Glandular epithelium lining the secreting portion of glandsFunctions ofEpithelial Tissue1.Protection e.g. skin2.Absorption e.g. intestinal cells absorb nutrients3.Filtration e.g. kidney filters waste substances that leave the blood and are become excretedwith urine4.Secretion e.g. glandsClassification of Epithelium:Required reading Fig 5.3 p. 148 and Table5 5.2 and 5.3 pages 149-152According to thearrangementin layers, epithelium can be classified into:1.Simple:single layer of cells2.Stratified:multiple layers
2According to theshapeof the cells, epithelium can be classified into:1.Squamous:flat cells like fish scales (squam = scale)2.Cuboidal:cube-shaped like dice3.Columnar: small columnsNote that:a. The shape of the nuclei of different cells will vary in accordance with the shape ofthe cell.b. Stratified epithelium is named according to the shape of the cells in the apical layer.A.Simple Epithelium1.Simple squamous▪ Single layer of flat cells lying on a basement membrane▪ Permeable, allowing substances to diffuse through, such as in lung alveoli, across bloodcapillaries, or glomerular capsule of the kidney.▪ Forms serous membranes lining the ventral cavity and covering organs (pericardium, pleura,and peritoneum).

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