Every cell of the body needs nourishment, yet most cells cannot leave their position in the body and travel to a food source, so the food must be converted to a usable form and delivered. The digestive system, with the help of the circulatory system, acts like a gigantic “meals on wheels,” providing nourishment to over a hundred trillion “customer” cells in the body. It also has its own quality control and waste disposal system.
The digestive system provides the body with water, electrolytes, andother nutrients. To do this, the digestive system is specialized to ingest food, propel it through the digestive tract, digest it, and absorb water, electrolytes, and other nutrients from the lumen of the gastrointestinal tract. Once these useful substances are absorbed, they are transported through the circulatory system to cells, where they are used. The undigested portion of the food is moved through the digestive tract and eliminated through the anus.
This chapter presents the general anatomy of the digestive system (p. 878), followed by descriptions of the functions of the digestive system (p. 878), the histology of the digestive tract (p. 880), the regulation of the digestive system (p. 881) and the peritoneum (p. 882). The anatomy and physiology of each section of the digestive tract and its accessory structures are then presented: the oral cavity (p. 884), pharynx (p. 890), esophagus (p. 890), along with a section on swallowing (p. 890), stomach (p. 892), small intestine (p. 900), liver (p. 903), gallbladder (p. 908), pancreas (p. 909), and large intestine (p. 912). Digestion, absorption, and transport (p. 915) of nutrients are then discussed, along with the effects of aging on the digestive system (p. 921).