The colon wall has four distinct layers. The innermost layer is the mucosa, which is responsible for secretion and absorption. It also protects the underlying tissues. The submucosa contains loose connective tissue, glands, blood vessels, lymphatic vessels, and nerves. The muscular layer is responsible for the movements of the intestine. The inner muscle layer is composed of circular fibers that decrease the diameter of the intestine when they contract. In contrast, the outer muscular layer is composed of longitudinal fibers that shorten the intestine when they contract. Together, these layers act in a coordinated fashion to propel and mix the intestinal contents. The outermost layer, or serosa, protects the inner tissues and secretes a fluid that helps lubricate the organs in the abdominal cavity.