BI13_Ch4 Text Notes


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ANATOMY AND PHYSIOLOGY 1 TEXT NOTES Chapter 4 – Tissue: The Living Fabric 1. GENERAL a. Tissue – groups of cells that are similar in structure and perform a common or related function. i. The four primary types of tissue are epithelial (covering), connective (support), muscle (movement), and nervous (control). b. Histology – the study of tissues. 2. EPITHELIAL TISSUE a. Epithelial Tissue (Epithelium) – is a sheet of cells that covers a body surface or lines a body cavity. It forms boundaries between different environments and occurs in the body as: i. Covering and Lining Epithelium – forms the outer layer of the skin, dips into and lines the open cavities of the cardiovascular, digestive, and respiratory systems, and covers the walls and organs of the closed ventral body cavity. ii. Glandular Epithelium – fashions the glands of the body. iii. Epithelium functions include: protection, absorption, filtration, excretion, secretion, and sensory reception. b. Special Characteristics of Epithelium i. Epithelial tissues have many characteristics that distinguish them from other tissue types. 1) Polarity. a) All epithelia have an apical surface , which is an upper free surface exposed to the body exterior or cavity of an internal organ. It also has a lower attached basal surface . b) All epithelia exhibit apical-basal polarity , that is regions near the apical surface differ from those near the basal surface , a situation maintained, at least in part, by the highly ordered cytoskeleton of epithelial cells. in both structure and function. c) Some apical surfaces are smooth, but most have Microvilli , fingerlike extensions of the plasma membrane which tremendously increase the exposed surface area. d) Lying adjacent to the basal surface of an epithelium is a thin supporting sheet called the basal lamina , a noncellular adhesive sheet consisting largely of glycoproteins secreted by the epithelial cells. i) The basal lamina acts as a selective filter that determines which molecules diffusing from the underlying connective tissue are allowed to enter the File: f62b27ce91bd28c7ebd0880a565dfb06f8d8db8c.doc Updated: 8/14/09
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TEXT NOTES Chapter 4 Page 2 epithelium. 2) Except for glandular epithelia, epithelial cells fit close together for form continuous sheets. 3) All epithelial sheets rest upon and are supported by connective tissue, a) Just under the basal lamina is the reticular lamina , a layer of extracellular material containing a find network of collagen protein fibers that “belongs to” the underlying connective tissue. b) The basal lamina and reticular lamina form the basement membrane , which reinforces the epithelial sheet and defines the epithelial boundary. 4)
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