Digestion is the process of breaking down food into nutrients. There are two types of digestion: mechanical and chemical. In mechanical digestion, large chunks of food are broken down into small pieces. Mechanical digestion begins in the mouth and involves physical processes such as chewing. This process continues in the stomach as the food is mixed with digestive juices. In chemical digestion, large food molecules are broken down into small nutrient molecules. This is a chemical process which also begins in the mouth as saliva begins to break down food and continues in the stomach as stomach enzymes further digest the food.

Absorption is the process that allows substances one eats to be taken up by the blood. After food is broken down into small nutrient molecules, the molecules are absorbed by the blood. After absorption, the nutrient molecules travel in the bloodstream to cells throughout the body. This happens mostly in the small intestine.

Some substances in food cannot be broken down into nutrients. They remain behind in the digestive system after the nutrients are absorbed. Any substances in food that cannot be digested and absorbed pass out of the body as solid waste. The process of passing solid food waste out of the body is called elimination.

Digestive System

Nutrients in the foods one eats are needed by the cells of the body. How do the nutrients in foods get to the body cells? What organs and processes break down the foods and make the nutrients available to cells? The organs are those of the digestive system. The processes are digestion and absorption.

The digestive system is the body system that breaks down food and absorbs nutrients. It also gets rid of solid food waste. The digestive system is mainly one long tube from the mouth to the anus known as the gastrointestinal tract (GI tract). The main organs of the digestive system include the esophagus, stomach, and the intestine, and are pictured below (Figure below). The intestine is divided into the small and large intestine. The small intestine has three segments. The ileum is the longest segment of the small intestine which is well over 10 feet long. The large intestine is about 5 feet long.

Figure 1.  The Digestive System

Summary

• The digestive system is the body system that breaks down food, absorbs nutrients, and gets rid of solid wastes.
• Digestion is the process of breaking down food into nutrients while absorption is the process that allows nutrients to be taken up by the blood.