Epithelial cells join together to form epithelial membranes or tissue. At times called the epithelium, these sheets cover the outer surface of the body, helping create the form the body, as well as line body cavities. The primary job of epithelial tissue is to protect, but it is also involved in filtration, secretion, and absorption.
Types of Membranes
Epithelial membranes are classified as either cutaneous, meaning the skin, mucous, or serous. Mucous membranes, which line all cavities that are open to the outside, include the digestive and respiratory tract. Serous membranes, which are not open to the outside of the body, line the abdominal and thoracic cavities.
The skin, which is composed of epithelial cells, protects the body from invasion of germs, as well as from the sunlight.
Epithelium of the respiratory tract protects the body by filtering out dirt and particles and cleaning the air that is inhaled.
Epithelial cells form glands of the body. These glands secrete hormones and enzymes. Epithelium also may secrete wax, perspiration, digestive enzymes, and milk.
The organs of the digestive tract have an abundance of epithelial cells, which function to absorb water and digested food. These cells play a large part in the proper digestion of food.