Functions of Epithelia
The major functions of epithelia are
1.Protecting underlying structures. Examples include the outer layer of the skin and the epithelium of the oral cavity, which protect the underlying structures from abrasion.
2.Acting as a barrier. Epithelium prevents many substances from moving through it. For example, the epithelium of the skin acts as a barrier to water and reduces water loss from the body. The epithelium of the skin also prevents many toxic molecules and microorganisms from entering the body.
3.Permitting the passage of substances. Epithelium also allows many substances to move through it. For example, oxygen and carbon dioxide are exchanged between the air and blood by diffusion through the epithelium in the lungs.
4.Secreting substances. Sweat glands, mucous glands, and the enzyme-secreting portion of the pancreas are all composed of epithelial cells.
5.Absorbing substances. The cell membranes of certain epithelial tissues contain carrier proteins that regulate the absorption of materials. For example, the epithelial cells of the intestines absorb digested food molecules, vitamins, and ions.
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