Mucus

Mucus, oily material secreted by cells in the mucous membranes, which are the soft, skinlike linings that protect many of the body’s organs. Mucus consists mainly of mucin, a compound of protein and carbohydrate. It also contains dead tissue cells, white blood cells, salts, and water.

Mucus from membranes and glands lubricates the eyes. In the respiratory system, it helps keep smoke and dust from entering the lungs. Mucus forms a smooth, slippery surface in the mouth and throat, making it easier to swallow food. In the stomach, mucus provides a protective coating that helps prevent the stomach wall from being damaged by gastric juice, which is highly acidic. In the female reproductive system, mucus flows from the cervix to lubricate and cleanse the vagina.

Disease-causing agents entering the body often make first contact at a mucosal surface, and the natural flow of mucus is a key part of the body’s immune system. Mucosal barriers trap viruses, bacteria, and toxins, making them easy targets for such disease-fighting microorganisms as white blood cells.