Anatomy & Physiology

Anatomy & Physiology Study Guide scar tissue is usually “remodeled” and gradually assumes a more normal appearance. The cell population in the area gradually increases; some cells migrate to the site, and others are produced. 4.6 Chapter Four Review The four tissue types are epithelial, connective, muscle, and neural: • Tissues are collections of specialized cells and cell products that perform a relatively limited number of functions. The four tissue types are epithelial tissue, connective tissue, muscle tissue, and neural tissue. • Histology is the study of tissues. Epithelial tissue covers body surfaces, lines cavities and tubular structures, and serves essential functions: • Epithelial tissue includes epithelia and glands. An epithelium is an avascular layer of cells that forms a barrier that provides protection and regulates permeability. Glands are secretory structures derived from epithelia. Epithelial cells may show polarity, which is an uneven distribution of cytoplasmic components. • A basal lamina attaches epithelia to underlying connective tissues. • Epithelia provide physical protection, control permeability, provide sensation, and produce specialized secretions. Gland cells are epithelial cells that produce secretions. In glandular epithelia, most cells produce secretions. • Epithelial cells are specialized to perform secretory or transport functions and to maintain the physical integrity of the epithelium. • Many epithelial cells have microvilli. • The coordinated beating of the cilia on a ciliated epithelium moves materials across the epithelial surface. • Cells can attach to other cells or to extracellular protein fibers by using cell adhesionmolecules (CAMs) or at specialized attachment sites called cell junctions. The three major types of cell junctions are occluding junctions (tight junctions), gap junctions, and macula adherens (desmosomes). • The inner surface of each epithelium is connected to a two-part basal lamina consisting of a clear layer (lamina lucida) and a dense layer (lamina densa). Divisions by germinative cells continually replace the short-lived epithelial cells. Cell shape and number of layers determine the classification of epithelia: • Epithelia are classified by the number of cell layers and the shape of the cells at the apical surface. • A simple epitheliumhas a single layer of cells covering the basal lamina; a stratified epithelium has several layers. The cells in a squamous epithelium are thin and flat. Cells in a cuboidal

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