Digestion is the transformation of food into assimilable substances, carried out in the digestive or digestive system, through two types of processes: mechanical and chemical .

Mechanical digestion

Mechanical digestion is performed with chewing , swallowing and the movements that take place in the digestive tract, called peristaltic movements or peristalsis.

Chewing and Swallowing

In digestion, in its mechanical process, food is chewed and reduced to very small pieces, with the help of teeth and tongue. The contact of food with saliva facilitates its passage through the digestive tract.

Swallowing process

After chewing and salivation, the food cake is formed and swallowed. During swallowing the soft palate is retracted upwards and the tongue pushes the food backwards, throwing it into the pharynx , which contracts and projects the food bolus into the esophagus .

When we swallow, the epiglottis closes the glottis, preventing food from going into the trachea .


The esophagus , is a muscular conduit that performs involuntary contractions called peristaltic movements or peristalsis , which leads the bolus to the stomach , where the chemical process of digestion begins.

See also: Digestive System, Digestive System

Chemical Digestion

In chemical digestion , food is broken down into smaller particles thanks to the action of enzymes present in digestive juice, undergoing changes in its chemical composition.



In the stomach, the peristaltic movements mix the bolus with gastric juice, produced by the glands of the gastric mucosa. This juice contains hydrochloric acid , which maintains stomach acidity, providing a favorable condition for the work of enzymes in digestion.

The pepsin , the principal enzyme of the stomach, acts in the processing of proteins, enhancing the chemical digestion. The gastrin hormone (produced in the stomach when food comes into contact with its walls) regulates the action of pepsin, which transforms large molecules (polypeptides) into smaller molecules (dipeptides).

Protein Digestion starts in the Stomach and continues in the Small Intestine.

Food juice, the result of chemical digestion, is called chyme . The passage from the chyme to the intestine is controlled through a valve called pylorus .

Small intestine

Small intestine

In the small intestine most digestion and assimilation of nutrients occurs . Two regions are distinguished in it: the duodenum and the jejunum-ileum.

In the duodenum are released secretions of the liver and pancreas , which along with the enteric or intestinal juice, act on the chime (bolus which has the appearance of a white mass after passing through the gastric digestion).

  • The bile:and secretion of the liver, stored in the gallbladder , which is released in the duodenum via the common bile duct. The bile contains no digestive enzymes but bile salts (contains water and sodium bicarbonate, mainly) separating the fat into microscopic particles, facilitating the action of pancreatic enzymes on the lipid .
  • The pancreatic juice:is produced by the pancreas. The trypsin is an enzyme produced in the pancreas which acts on the proteins. It only becomes active when it reaches the duodenum and joins the enteric juice, transforming it into chymotrypsin .
  • The intestinal juice or enteric:is produced by the intestinal mucosa. It has enzymes that complete the digestion of lipids, proteins and carbohydrates .

At the end of the process carried out in the duodenum, the group of substances forms a viscous white liquid, called kilo , which goes to the jejunum-ileum.

In the jejunum ileum, most of the nutrients resulting from the digestion process are absorbed by the blood and carried to all the cells of the body. What is not absorbed – the water and the pasta, formed mainly of fibers – pass into the large intestine.

The dietary fiber are thus essential to the formation of stools and smooth functioning of the intestines.

Large intestine

The large intestine absorbs water and minerals that the small intestine has not assimilated in digestion. The material that has not been digested, forms the feces that are accumulated in the rectum (final part of the large intestine) and later pushed by peristaltic movements outwards, through the anus canal .


by Abdullah Sam
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