Epithelial cells are arranged in tightly packed layers that line the surfaces and cavities of tissues and organs throughout the body. It covers rang skins, respiratory tracts( nasal cavity and lungs ), alimentary tracts(oral cavity, stomach, intestines ), urogenital tract (kidney, vesicae, uterus and epididymis ), from all anacrine glnads (pancreas, gallbladder, mammary gland, salivary glands, lacrimal gland, sweat gland and etc. ), even some immune system organ (like thymus gland ).
The principle function of epithelial cells is to provide a protective layer for the organ they enclose but also provide other biological functions including secretion, selective absorption, filtration, protection and detection of sensation. The dysfunction of epithelial cells leads to a variety of diseases, infections and tumors. Therefore, epithelial cells are used in multiple research areas such as physiology, immunology, cytobiology, development and reproductive biology, molecular biology.