The digestion process

Digestion is the process through which food is physically and chemically transformed so that it can pass through the walls of the digestive tract and into the blood. This process involves a set of organs, regulated by nervous and hormonal mechanisms.

General feeding processes:

• Ingestion: begins in the mouth and includes the processes of chewing, insalivation and swallowing of food.

• Digestion: comprises a set of processes that convert the complex molecules of food into simpler units that can be absorbed and utilized. It begins in the mouth and continues to the small intestine.

• Absorption: is the process by which nutrients pass through the walls of the digestive tract into the blood. It occurs mainly through the walls of the small intestine.

• Expulsion: is the removal of undigested materials through defecation.

Organs and structures involved in the digestive process

The mouth: in the mouth, the fragmentation of the food is produced by chewing, crushed by the teeth and moved by the tongue, a muscular organ that also possesses the sense of taste. During mastication, the saliva formed in the salivary glands, mixes with the food, to know the taste and to initiate the chemical digestion of the starch, converting it into maltose.

The food already crushed, takes a pasty appearance, called food bolus, which is pushed towards the pharynx, by the tongue.

Pharynx: it is a structure located in the neck that communicates the oral cavity and the nasal cavity with the esophagus and the larynx respectively. It is where the swallowing of food takes place, which consists of the transit of the food bolus from the mouth to the pharynx and from the pharynx to the esophagus. In the pharynx there is a humid cartilaginous structure, called epiglottis that folds during swallowing, to avoid the passage of parts of the alimentary bolus to the respiratory tract.

Esophagus: the esophagus is a muscular tube that communicates the pharynx with the stomach. It has a lower sphincter called the cardia, which facilitates the passage of food from the esophagus to the stomach and prevents the stomach contents from returning to the esophagus.

Stomach: gastric digestion takes place in the stomach, the food bolus is stored and mixed with gastric acid and protein-degrading digestive enzymes. Stomach cells also secrete a glycoprotein that allows the absorption of vitamin B12.

The mixture produced, called chyme, is produced by the action of smooth and undulating movements of the stomach muscles, where it remains for a period of two to four hours, depending on multiple factors, such as the type of food. Foods rich in carbohydrates pass quickly, while those rich in fats remain longer.

Pancreas: it is in charge of producing juices capable of breaking down the carbohydrates, fats and proteins contained in food. These juices are carried to the small intestine, where the chemical decomposition of numerous complex molecules takes place.

Liver: the liver produces bile, a digestive juice capable of digesting some fats and vitamins. Gallbladder: the bile produced by the liver is stored in the gallbladder and sent to the small intestine during digestion.

Small intestine: the small intestine is the section of the digestive tract that connects the stomach with the large intestine. It serves as the body's digestion, absorption and protective barrier.

The chyme, a substance resulting from the processing of food in the stomach, passes into the small intestine, where it is mixed with three different liquids:

• Bile.

• Pancreatic juice.

• Intestinal enzymes.

In this phase, complex molecules are broken down into simpler units that can be absorbed and utilized. These substances pass through the microvilli of the small intestine wall into the blood. The nutrients absorbed into the blood are transported to the liver for filtration, toxin removal and nutrient processing.

Large intestine: In the large intestine, digestion waste, cellular debris and waste water from the small intestine are converted into feces, and b vitamins and vitamin K can be synthesized.

Rectum: the rectum is the lower end of the large intestine, it is responsible for storing feces until they are expelled during defecation.

Regulators of digestion

Hormonal regulators: the main hormones that control the functions of the digestive system are produced and released from mucosal cells of the stomach and small intestine. The hormones that control digestion are:

• Gastrin: gastrin secretion is stimulated by the arrival of food in the stomach. It causes the stomach to produce hydrochloric acid, a substance that dissolves and digests some foods and is involved in the normal growth of the mucosa of the stomach and small intestine.

• Secretin: causes the pancreas to secrete a digestive juice rich in bicarbonate, stimulates the production of pepsin, an enzyme that digests proteins and the production of bile in the liver.

• Cholecystokinin: triggers the production of enzymes in the pancreatic juice and the growth of the pancreas. It also causes the gallbladder to empty.

• Gastric inhibitory peptide: slows gastric emptying and induces insulin secretion.

• Vasoactive inhibitory peptide: stimulates the production of enzymes in the pancreas and bile from the gallbladder.

Nerve regulators: the nerves that control the work of the digestive tract are divided into two groups:

• Extrinsic nerves: they cause the release of acetylcholine and adrenaline:

• Acetylcholine causes the muscles of the digestive organs to contract more forcefully and better push food and liquids through the digestive tract. It also causes the stomach and pancreas to produce more gastric juices.

• Adrenaline relaxes the muscle of the stomach and intestines and decreases blood flow to these organs.

Intrinsic nerves: these are the most important. They form a network embedded in the walls of the esophagus, stomach and small intestine. These nerves, when the walls of the organs are stretched by the presence of food, release many different substances that accelerate or delay the movement of food and the production of juices in the organs of the digestive system.

Recommendations for good digestion

Distribute the food to be consumed during the day in four or five light meals. Avoid abundant meals, especially at night. Establish meal times, in order to achieve stability of the biological clock.

Eat in a relaxed environment, calmly, chewing food properly. Limit the use of medications. Reduce the consumption of carbonated beverages and junk food.

Eat foods containing vegetable fiber, such as fruits, vegetables and cereals. Wait at least one hour after meals to perform intense physical activities. Drink more than two liters of water distributed throughout the day. Avoid drinking alcoholic beverages without moderation.