#TheBodyPhysiology: Primary Functions Of The Digestive System

✒️ - By Aan Gray

The digestive system is the organ system that processes food, extracts nutrients from it, and eliminates the residue. It does this in five stages:

1. Ingestion, the selective intake of food;
2. Digestion, the mechanical and chemical breakdown of food into a form usable by the body;
3. Absorption, the uptake of nutrient molecules into the epithelial cells of the digestive tract and then into the blood or lymph;
4. Compaction, absorbing water and consolidating the indigestible residue into feces; and finally,
5. Defecation, the elimination of feces.

The digestion stage itself has two facets, mechanical and chemical. Mechanical digestion is the physical breakdown of food into smaller particles. It is achieved by the cutting and grinding action of the teeth and the churning contractions of the stomach. Mechanical digestion exposes more food surface to the action of digestive enzymes. Chemical digestion is a series of hydrolysis reactions that break dietary macromolecules into their monomers: polysaccharides into monosaccharides, proteins into amino acids, fats into monoglycerides and fatty acids, and nucleic acids into nucleotides.

It is carried out by digestive enzymes produced by the salivary glands, stomach, pancreas, and small intestine. Some nutrients are already present in usable form in the ingested food and are absorbed without being digested: vitamins, free amino acids, minerals, cholesterol, and water.
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