ABSTRACT
The organs and structures of the digestive system can be divided into two groups: those of the gastrointestinal tract (GIT) and the accessory digestive organs such as the salivary glands, pancreas and liver. The GIT consists of four separate layers: peritoneum, muscle, submucosa and mucosa. When the stomach is empty, the gastric mucosa secretes a hormone called ghrelin that stimulates receptors in the lateral hypothalamus and inhibits receptors in the ventromedial hypothalamus in order to produce the sensation of hunger. The mouth or oral cavity is the point for normal ingestion of food and the first stage of mechanical and chemical breakdown. Saliva is essential to lubricate the mouth, assist with swallowing, protect the teeth against bacteria and to aid chemical digestion of food. Pancreatic enzymes include pancreatic amylase that, like salivary amylase secreted in the mouth, helps to digest carbohydrate. The pancreas also produces protein-digesting enzymes called trypsin and chymotrypsin.
