Phases of Human Digestion: Process & Function

The Digestive Process

There are three phases in food processing: digestion, absorption, and the expulsion of waste. The movement of food through the digestive tract is known as peristaltic movements. These consist of the narrowing of the tube through the contraction of the muscles of the walls. The muscles contract successively.

Digestion

Types of Digestion

• Mechanical digestion consists of cutting, crushing, moving, and diluting foods.
• Chemical digestion is done through the action of various substances, which attack the foods and bring about chemical changes.

Stages of Food Digestion

• Digestion in the mouth is a result of mastication and salivation. Mastication cuts and crushes the food. Saliva is a liquid produced by the salivary glands in the mouth. Saliva contains substances that act chemically on the foods.
• After swallowing, gastric digestion begins in the stomach. Physical and chemical digestion occur simultaneously in the stomach. The foods move and are softened thanks to the movement of the walls of the stomach, and they are mixed with gastric juices. These contain substances like hydrochloric acid, which act chemically on the foods. A pulp known as chyme is produced, and this gradually leaves the stomach via the pylorus.
• In the small intestine, specifically the duodenum, the chyme is mixed with intestinal juices (made by the walls of the duodenum), bile (produced by the liver), and pancreatic juice (from the pancreas). The result is a milky fluid known as chyle.

Absorption and Elimination of Waste

• The chyle passes from the duodenum to the rest of the small intestine. The internal walls of these parts of the intestine are very rough and filled with intestinal villi, deep folds in the wall, and many blood vessels.
• Absorption consists of the useful substances in the food crossing through the intestinal wall and into the blood vessels.
• In the first part of the large intestine, the ascending colon begins to recover water and some ions, such as sodium. This continues in the transverse colon. Finally, the descending colon stores the feces, to be expelled via the anus.