Physiology Topics
Epithelial tissue consists of densely packed cells arranged in continuous sheets, either in single or multiple layers. The apical surface of epithelial cells may be exposed to a body cavity or the exterior of the body. The basal surface adheres to adjacent connective tissue. The attachment between the basal surface and the connective tissue is a thin layer called the basement membrane, which commonly consists of two layers: the basal lamina (contains collagen fibers and other proteins) and the reticular lamina (contain reticular fibers and fibronectin).
Epithelial tissue has a nerve supply, but is avascular. Blood vessels are located in adjacent conective tissue. Because of its high mitotic rate, epithelial tissue constantly renews and repairs itself. It forms the epidermis, outer covering of organs, inner lining of blood vessels, ducts and body cavities.
Simple squamous epithelium consists of a single layer of flat cells. It is found were filtration and diffusion occurs. Simple cuboidal epithelium cells are cuboidal in shape, with aa centrally located nucleus. They perform secretion and absorption. Simple columnar epithelium cells are rectangular with their nucleus near the base. Goblet cells are modified columnar cells that secrete mucus. Other columnar cells are ciliated and help move materials, for example dust particles trapped in mucus, or the ovum as it travels into the uterus.
Stratified squamous epithelium cells are layered, with apical surface cells being flat, and deep layer cells being cuboidal or columnar. The basal cells continually undergo cell division. As new cells grow, the basal cells are pushed upward towards the apical surface. This is a more durable type of epithelium and can protect underlying tissues..
The function of glandular epithelium is secretion, which is accomplished be glandular cells that often .lie in clusters deep to the covering and lining epithelium. The secretion of endocrine glands enters the extracellular fluid and diffuses directly into the blood stream without following into a duct Exocrine glands secrete their products into ducts the empty sat the surface of lining epithelium or other free surface.
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