The human gastrointestinal tract, or GI tract, or GIT is an organ system responsible for consuming and digesting foodstuffs, absorbing nutrients, and expelling waste. The tract consists of the stomach and intestines, and is divided into the upper and lower gastrointestinal tracts. However, by the broadest definition, the GI tract includes all structures between the mouth and the anus. On the other hand, the digestive system is a broader term that includes other structures, including the digestive organs and their accessories. The tract may also be divided into foregut, midgut, and hindgut, reflecting the embryological origin of each segment. The whole digestive tract is about nine metres (30 feet) long. The GI tract releases hormones to help regulate the digestive process. These hormones, including gastrin, secretin, cholecystokinin, and ghrelin, are mediated through either intracrine or autocrine mechanisms, indicating that the cells releasing these hormones are conserved structures throughout evolution.
