When you eat foods—such as bread, meat, and vegetables—they are not in a form that the body can use as nourishment. Food and drink must be changed into smaller molecules of nutrients before they can be absorbed into the blood and carried to cells throughout the body.
Digestion is the mechanical and chemical breakdown of food into smaller components that are more easily absorbed into a blood stream, for instance. Digestion is a form of catabolism: a breakdown of large food molecules to smaller ones. The digestion is performed by the Digestive System.
The human gastrointestinal tract is the esophagus, the stomach and intestine, sometimes including all the structures from the mouth to the anus. (The “digestive system” is a broader term that includes other structures, including the accessory organs of digestion).
In an adult male human, the gastrointestinal (GI) tract is 5 metres (20 ft) long in a live subject, or up to 9 metres (30 ft) without the effect of muscle tone, and consists of the upper and lower GI tracts. The tract may also be divided into foregut, midgut, and hindgut, reflecting the embryological origin of each segment of the tract.
The GI tract always releases hormones to help regulate the digestive process. These hormones, including gastrin, secretin, cholecystokinin, and grehlin, are mediated through either intracrine or autocrine mechanisms, indicating that the cells releasing these hormones are conserved structures throughout evolution.
The diferent structures are:
Also there are some glands annexed:
- Salivary glands