The gastrointestinal (GI) tract is the greatest of the three major pathways into and out of the body, the other two being the skin and the respiratory tract. The GI tract contains and processes food from the time it is eaten until it is digested and absorbed or eliminated. The mucosa, or inner lining of the tract, is a mucous membrane. The submucosa consists of areolar connective tissue that binds the mucosa to the muscularis. The muscularis of the mouth, pharynx, and superior and middle parts of the esophagus contains skeletal muscle that produces voluntary swallowing. Skeletal muscle also forms the external anal sphincter, which permits voluntary control of defecation. The serosa is the superficial layer of those portions of the GI tract that are suspended in the abdominopelvic cavity. Peritonitis is an acute inflammation of the peritoneum. Salivary gland is any cell or organ that releases a secretion called saliva into the oral cavity.