Question

Give occurence and functions of epithelial tissue(epithilium) and its parts.

Answer 1

Functions of Epithelial Tissue

Epithelial tissue has a number of functions, which include protection against abrasion, radiation damage, chemical stress and invasion by pathogens. A single organ can have different types of epithelial tissue based on the substances to which different surfaces are exposed. Protective tissue tends to be thicker, made of multiple layers of cells and often has inclusions such as keratin to provide mechanical strength and resistance. The skin of most mammals contains layers of thick keratinized dead epithelial cells protecting them against water loss and other stresses. Similarly, the esophagus is also exposed to a wide range of different textures, pH levels and chemical compositions from food and drink. Therefore, it also contains protective epithelium. Due to its involvement in the digestive process, however, it remains non-keratinized, and secretes mucus to smoothen the passage of food.

Alternatively, epithelial tissue can be involved in absorption, secretion and movement of substances. These epithelia are usually thin, containing cilia or microvilli and are often made of one layer of cells. With the exception of the mouth and esophagus, the rest of digestive tract consisting of the stomach, small and large intestine is covered by these kinds of thin epithelia. These cells secrete enzymes and play an important role in selectively absorbing digested food. The small intestine is particularly noted for the presence of microvilli on the epithelium that increase the surface area for absorption. Epithelia in bronchioles of the lungs contain cilia that move mucus and improve immune function. Similar ciliated epithelia in the fallopian tubes move the egg from the ovaries towards the uterus.

Answer 2

Epithelial Tissue Function

Epithelial tissue covers the outside of the body and lines organs, vessels (blood and lymph), and cavities. Epithelial cells form the thin layer of cells known as the endothelium, which is contiguous with the inner tissue lining of organs such as the brain, lungs, skin, and heart. The free surface of epithelial tissue is usually exposed to fluid or the air, while the bottom surface is attached to a basement membrane.

The cells in epithelial tissue are very closely packed together and joined with little space between them. With its tightly packed structure, we would expect epithelial tissue to serve some type of barrier and protective function and that is certainly the case. For example, the skin is composed of a layer of epithelial tissue (epidermis) that is supported by a layer of connective tissue. It protects the internal structures of the body from damage and dehydration.

Epithelial tissue also helps to protect against microorganisms. The skin is the body's first line of defense against bacteria, viruses, and other microbes.