The Human Digestive system comprises of the:
- Gastrointestinal Tract
- Salivary glands
The latter 5 being the organs of digestion). The process of digestion is the breakdown of our food intake into smaller components which facilitates absorption into the body.
The process of digestion has three stages.
Gastric activity involved in digestion is divided into three stages known as the
- cephalic phase,
- gastric phase, and the
- intestinal phase.
These phases overlap and all three can occur simultaneously.
The first stage is the cephalic phase of digestion which begins with gastric secretions in response to the sight and smell of food.
This stage includes the mechanical breakdown of food by chewing, and the chemical breakdown by digestive enzymes, that takes place in the mouth.
Saliva contains digestive enzymes; these enzymes start to break down the food in the mouth.
Chewing, in which the food is mixed with saliva, begins the mechanical process of digestion. This is swallowed down the oesophagus to enter the stomach.
In the stomach the gastric phase of digestion takes place.
The food is further broken down by mixing with gastric acid until it passes into the duodenum that contains bile stored from the gallbladder made by the liver to help break down fat, in the third phase where it is mixed with a number of enzymes produced by the pancreas.
Digestion is helped by the chewing of food carried out by the tongue, and the teeth.
Gastric acid and the production of mucus in the stomach, are essential for the continuation of digestion.
Most of the digestion of food takes place in the small intestine. Water and some minerals are reabsorbed back into the blood in the colon of the large intestine.
The waste products of digestion exit the body from the anus via the rectum.