EPITHELIAL TISSUE
The Epithelial tissue or an epithelium (plural) is the covering, lining and glandular tissue of the body. Its functions include protection, absorption, excretion, filtration,secretion and sensory reception (Marieb, n, Elaine &HoehnKatja).
The epithelium tissue fascinated me becauseas my naive self, I thought that it only covered the outer body commonly known as the skin but I was wrong. The epithelial tissue can be found in the epidermis of the skin which lies between the inside and outside of the body, and the epithelial lining the urinary bladder which separate the underlying cells of the bladder wall from urine (Marieb, n, Elaine &HoehnKatja).
There are two forms of epithelial tissue in the body. 1) The covering and lining epithelium, which forms the outer layer of the skin, dips into the lines and open cavities of the urogenital, digestive, and respiratory systems and covers the walls and organs of the closed ventral cavity, and 2) The glandular epithelium which fashions the glands of the body (Marieb, n, Elaine &HoehnKatja).
The epithelial tissue is characterized by: 1) The Apical, basal polarity meaning that all epithelia have an upper free surface (apical surface)exposed to the body exterior or the cavity of an internal organ, and a lower attached basal surface, which both differ in structure and function. 2) Specialized contacts which except for glandular epithelia, epithelial cells fit closely together to form continuous sheets that help in the binding of cells together at various points(junctions) which help keep proteins in the apical region of the plasma membrane from diffusing into the basal region, therefore helping to maintain epithelial polarity. 3) Supported by connective tissue, epithelia consist of two lamina, (basal and reticular) to form the basement membrane which reinforces the epical sheet and helps it resist stretching and tearing, hence defining the epithelial boundary. 4) Avascular but innervated: As much as epithelium is avascular (contains no blood vessels), it is innervated (supplied by nerve fibers) and its cells are nourished by substances diffusing from blood vessels in the underlying connective tissue.5) Epithelium has a high regenerative capacity in that while some epithelia may be exposed to friction or damage by external environments like bacteria, acids and smoke, epithelial cells can replace lost cells by cell division as long as they receive adequate nutrition.(Marieb, n, Elaine &HoehnKatja).
Each epithelium has two names; Simple epithelium which consist of a single cell layer, are located where absorption,secretion and filtration occur and consist of a thin epithelial barrier. Stratified epithelia is however composed of two or more cells layers stacked up on top of each other,and is found in abrasion areas like the lining of the mouth and the skin surface (Marieb, n, Elaine &HoehnKatja).
All epithelial cells have a polyhedral shape which allows the cells to be closely packed. There are three common shapes that vary in height namely, the squamous cells are flattened and scale-like, Cuboidal cells are boxlike as tall as they are wide, and columnar cells which are tall and column shaped.(Marieb, n, Elaine &HoehnKatja).
Do you think the shape of the epithelial cell would affect the shape of its nucleus?