Functions of the Digestive System
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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.
