Friday, October 22, 2010
Kinds of Epithelial Tissues
Friday, October 22, 2010 by Faizan Bhatti
Epithelial tissue exists in many structural forms and mostly either covers or lines an organ or a duct. These cells typically consist of renewable sheets of cells that have surface specialization adapted for their specific roles. All epithelial cells are supported by underlying basement membrane which is condensed form of connective tissue. Epithelial tissues are classified on the basis of shape and number of layers present. Epithelium can be simple, stratified. Individual epithelial cells can be flat, cube shaped or column like. Epithelial tissues absorb, transport, excrete, protect and contain nerve cells for sensory reception. The size, shape and arrangement of the epithelial cells are related to these specific functions.
(1) Simple squamous epithelium:
It consists of single layer of tightly packed, flattered cells with disc shaped central nucleus. They are located in air sacs of the lungs, kidney glomeruli, lining of heart, blood vessels and lymphatic vessels. It allows passive diffusion of gases and tissue fluids into and out of cavities.
(2) Simple Cuboidal epithelium:
It consists of single layer of tightly packed. These cells are smaller in size cube or box with almost central nucleus and have pentagonal or hexagonal outline. They are located in kidney tubules, small glands and surface of the ovary. These cells are responsible in secretions and absorption.
(3) Simple columnar epithelium:
It consists of single layer of elongated cells with an elongated nucleus located near the basal end of the cell. These cells often bear minute finger like projection called microvilli that increase its absorptive surface area. In some cases they also develop cilia and become ciliated cells as in the lining of female reproductive tract. Some are specialized as the global cells that secrete mucus. They are located in the lining of digestive tract, gall bladder, female reproductive tract and excretory ducts of some glands. They are highly absorptive in nature and as such are present along the intestinal tract of most animals. They are also responsible for absorption of different material and enzyme secretion.
(4) Pseudostratified ciliated columnar epithelium:
It consists of columnar cells with a tuft of cilia at the top except the goblet cells. The cells of psendostratified ciliated columnar epithelium appear stratified or layered as each cell has two or more nuclei. They are located in the lining of branch, uterine, tubes and some regions of uterus. These cells help the reproductive cells and mucous to move by ciliary action.
(5) Stratified squamous epithelium:
It consists of many layers of cells. They form the lining of oral cavity, oesophagus, digestive canal and vagina. Some keratinized cells also line the surface of the skin. They protect the underlying tissues against abrasion. The basal layers of cell undergo division, pushing the cells towards the surface where they are sloughed off and replaced by new cells form beneath.Tags: Biology , Zoology
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