Digestion

Digestion is the process through which the body breaks down food into smaller, more easily absorbed components. This process involves both mechanical and chemical processes and occurs in the digestive system, which includes the mouth, esophagus, stomach, small intestine, and large intestine.

Mechanical Digestion

Mechanical digestion refers to the physical breakdown of food into smaller pieces. This process begins in the mouth, where food is chewed and mixed with saliva to form a soft mass called bolus. The bolus then travels down the esophagus to the stomach, where it is further broken down by the churning action of the stomach muscles.

Chemical Digestion

Chemical digestion involves the breakdown of food using enzymes and other digestive juices. In the mouth, salivary amylase starts the digestion of starches. In the stomach, gastric juices containing hydrochloric acid and pepsin work to break down proteins. Once food enters the small intestine, it is mixed with bile from the liver and enzymes from the pancreas to further break down fats, proteins, and carbohydrates into their basic building blocks.

The Role of the Small Intestine

The small intestine is the primary site of nutrient absorption. Its inner surface is lined with tiny, finger-like projections called villi, which increase the surface area for absorption. Nutrients such as glucose, amino acids, and fatty acids are absorbed through the villi and into the bloodstream to be used by the body for energy, growth, and repair.

The Role of the Large Intestine

After the small intestine has absorbed all the nutrients it can, the remaining indigestible material moves into the large intestine, or colon. Here, water is absorbed and the waste material is formed into feces, ready to be eliminated from the body through the rectum and anus.

Study Guide

1. What is digestion?
2. Describe mechanical digestion and give examples.
3. What is chemical digestion and where does it occur?
4. Explain the role of the small intestine in digestion.
5. What happens in the large intestine?