Functions of the Digestive System

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Chapter: Anatomy and Physiology for Health Professionals: Digestive System

The functions of the digestive system consist of a series of seven essential steps:

Functions of the Digestive System

The functions of the digestive system consist of a series of seven essential steps:

1. Ingestion: Materials enter the digestive tract via the mouth.

2. Propulsion: The movement of food, which includes voluntary swallowing and involun-tary peristalsis, which is the primary means of propulsion. Peristalsis involves alternating waves of muscular contraction and relax-ation in the walls of the alimentary canal.

3. Mechanical breakdown: Materials are crushed and broken into smaller fragments, making them easier to move through the digestive tract. Enzymes begin to attack the particles during chewing, as the teeth and tongue are used to tear and mash food. ­Additional mechanical processing is provided by the mixing motions of the stomach and ­intestines. Mechanical processing increases ingested foods’ surface areas. Segmentation mixes foods with digestive juices, improving their absorption by moving various parts of the food mass over the intestinal wall ­repeatedly.

4. Digestion: The chemical breakdown of food into particles that are small enough to be absorbed by the digestive epithelium from the lumen or cavity of the canal; sim-ple molecules such as glucose are absorbed intact, whereas polysaccharides, proteins, and triglycerides must first be broken down before they can be absorbed. This is a cata-bolic process.

5. Secretion: Release of water, acids, buffers, enzymes, and salts by the epithelium and glandular organs of the digestive tract.

6. Absorption: The movement of organic sub-strates, electrolytes, vitamins, and water across the epithelium of the digestive tract into the interstitial fluid. Organic substrates are molecules acted on by enzymes. Absorp-tion occurs via active or passive transport into blood or lymph.

7. Defecation: The removal of waste products from body fluids via secretions from the digestive tract and glandular organs; after mixing with residue that cannot be digested, these waste products become feces, which are eliminated.

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