The Gastrointestinal System

Parts of the system. The gastrointestinal system might be thought of as a long passage through which food passes. It has glands attached to it that pour chemicals into the passage. These chemicals digest the food as it passes along the passageway. The purpose of this system is to convert the food you eat into substances your cells can use.

The mouth, stomach, intestines, and other parts of the gastrointestinal system digest food by both chemical and muscular action. The glands in the system secrete fluids that break down the foods into usable substances. The muscles in the mouth, esophagus, stomach, and intestines break the food into small particles and keep the food moving through the various stages of chemical digestion.

You will be able to understand all these processes when you read how foods pass through the digestive system. Every food is acted upon by one or more chemicals in the system.

Digestion in the mouth. The first step in digesting food takes place in the mouth, where you chew food. By chewing food, you break it into bits small enough for the digestive juices to work on. The saliva in the mouth is the first digestive juice. It breaks down some of the carbohydrates, or starches, and changes them to a simple sugar.

After food is chewed and mixed with saliva, it is forced down the esophagus by muscular activity called peristalsis. Peristalsis is the progressive contracting of ringlike muscles in the esophagus that forces the food down the canal into the stomach.

Digestion in the stomach. When the food gets to the stomach, it is mixed with hydrochloric acid and agitated by muscular action. The acid makes it possible for several special chemicals, called enzymes, to act on the food. These chemicals break down the protein, curdle milk, and convert fat into a substance the body can use.

In the intestine. When the liquid food passes into the small intestine, it is acted upon by still more enzymes. Actually, most of the digestion takes place in the intestine. In addition to the enzymes secreted by the walls of the small intestine, other secretions act on the liquified food. The food moves along the intestine by peristaltic action, and by the time it reaches the large intestine, or colon, the food value has been taken out of it.

Food enters the blood. As you have learned earlier, the food must enter the blood stream before it can feed the cells of the body. This is accomplished by tiny projections called villi that stick out into the intestines. The liquified foods pass through the thin walls of the villi and into the capillaries and lymph vessels, which are crowded into each projection.

The walls of the intestine are so lined with villi that they resemble the surface of a turkish towel. Once the digested protein and carbohydrates are passed into the blood and lymph, they are transported directly to the cells. These substances feed the cells and keep the body alive.

Related Posts

1. The Circulatory System
2. The Respiratory System
3. The Human Body
4. The Systems of the Body
5. The Nervous System