The digestive system is made up of a series of organs that use mechanical and chemical processes to take in food, break it down, extract nutrients and energy, and lastly, to eject the waste of this process.
The mouth begins the process as the entrance for food. When chewing, the teeth mechanically break down the food. The salivary glands in the mouth release the amylase enzyme which chemically breaks down starch and fat. The saliva moistens the food and regulates the pH level within the mouth.
Muscular contractions take the food down the esophagus and into the stomach. In the stomach, food is further broken down into smaller pieces. Food is used by cells, so it must be further broken down for the tiny cells to be able to absorb it. The stomach releases acidic gastric juices and uses muscular contractions to break down the food.
From the stomach, the small pieces of broken down food move into the small intestine. This is where the bulk of the nutrient extraction takes place. In the small intestine, food is mixed with bile and pancreatic juices. Bile and pancreatic juice break down the nutrients in the food so that they can be absorbed by the blood. The villi in the inner intestine gather the nutrients for absorption.
Not all food is useful to the body. This is waste and is passed on to the colon which separates the liquid from the solid matter waste and sends the different materials to the anus or urinary tract for expulsion.