Mechanical Digestion
Mechanical digestion is carried out through chewing , swallowing and movements that occur in the digestive tract, called peristaltic movements or peristalsis.
Chewing and Swallowing
During digestion, in its mechanical process, food is chewed and reduced to very small pieces, with the help of the teeth and tongue. The contact of food with saliva facilitates its passage through the digestive tract.
After chewing and salivation, the food bolus 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 .
Esophagus
The esophagus is a muscular duct that carries out involuntary contractions called peristaltic movements or peristalsis , which carry the food bolus to the stomach , where the chemical process of digestion begins.
Chemical Digestion
In chemical digestion , food is broken down into smaller particles thanks to the action of enzymes present in the digestive juice, undergoing changes in its chemical composition.
Stomach
In the stomach, peristaltic movements mix the food bolus with gastric juice, produced by the glands of the gastric mucosa. This juice contains hydrochloric acid , which maintains stomach acidity, providing favorable conditions for the work of enzymes in digestion.
Pepsin , the main enzyme in the stomach, acts to transform proteins, intensifying chemical digestion. The hormone gastrin (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) .
The food juice resulting from chemical digestion is called chyme . The passage of chyme into the intestine is controlled by a valve called the pylorus .
Small intestine
Most of the digestion and assimilation of nutrients takes place in the small intestine . Two regions can be distinguished: the duodenum and the jejunum-ileum.
Secretions from the liver and pancreas are released into the duodenum , which, together with enteric or intestinal juice, act on the chyme (a bolus of food that looks like a white mass after passing through gastric digestion).
- Bile : is the secretion of the liver, stored in the gallbladder , which is released into the duodenum through the common bile duct. Bile does not contain digestive enzymes, but rather bile salts (mainly water and sodium bicarbonate) that separate fats into microscopic particles, facilitating the action of pancreatic enzymes on lipids .
- Pancreatic juice : produced by the pancreas. Trypsin is one of the enzymes produced in the pancreas, which acts on proteins. It only becomes active when it reaches the duodenum and joins the enteric juice, transforming into chymotrypsin .
- Intestinal or enteric juice : is produced by the intestinal mucosa. It contains enzymes that complete the digestion of lipids, proteins and carbohydrates .
At the end of the process carried out in the duodenum, the set of substances forms a viscous white liquid, called chyle , which goes to the jejunum-ileum.
In the jejunum-ileum, a large part 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 – water and food mass, mainly made up of fiber – passes to the large intestine.
Dietary fiber is therefore essential for the formation of feces and the proper functioning of the intestines.
Large intestine
The large intestine absorbs water and mineral salts that the small intestine did not assimilate during digestion. The undigested material forms feces, which accumulate in the rectum (the final part of the large intestine) and are subsequently pushed out through peristaltic movements through the anus .