WHAT IS MECHANICAL DIGESTION? - ANATOMY AND PHYSIOLOGY - 2025

The mechanical digestion is a process group that together with chemical digestion, make up the overall process of digestion of food in our body. It is specifically responsible for the grinding, transportation and mixing of food throughout the digestive tract, without getting involved with the modification of its chemical composition.

The digestive system in humans is primarily made up of the mouth, pharynx, esophagus, stomach, small intestine, and large intestine. Within each of these organs, mechanical and chemical digestion processes occur that result in general digestion.

In such a way that mechanical digestion is a set of specific and differentiated threads of chemicals. The mechanical digestive functions produce voluntary and involuntary contractions and relaxations of muscles.

Involuntary movements occur in response to reflexes caused by other digestive movements, or to both hormonal and neurological stimuli.

In mechanical digestion, three main functions are performed. The first is the mechanical division of food.

On the other hand, within mechanical digestion there are movements of different muscles and sphincters that produce two effects: the movement of the food bolus along the digestive tract, and the mixing of the food bolus with different digestive secretions.

Processes within mechanical digestion

Mechanical digestion includes the following processes:

Chewing

The chewing process occurs in the mouth, also called the "oral cavity." It involves the grinding of food through the teeth - especially the molars - and the tongue, with the help of additional coordination of movements between the muscles of the jaw, cheeks and lips.

The result of this grinding is the food that is crumbled into much smaller pieces, which at the same time that they are chewed, are moistened with saliva in the process of insalivation. This mass produced is called a food bolus.

In this way, from insalivation and chewing, the bolus is formed, which is much easier to ingest. The chewing movements are voluntary, and are activated by the presence of food.

Swallowing process

The swallowing process is one in which the food bolus passes from the mouth to the stomach, passing through the pharynx and esophagus. It occurs in three stages:

In the first stage, using the tongue, the person makes a voluntary push of the food bolus towards the pharynx.

Then, thanks to the impulse of the previous step, the food bolus passes completely through the pharynx to pass into the esophagus.

At the entrance to the esophagus, a sphincter located there called the "upper esophageal sphincter" relaxes and allows the bolus of food to enter the esophagus. Already in the esophagus, the food bolus goes down through it thanks to the peristalsis process.

Peristalsis produces, in a coordinated way, a progression of wavy movements of contractions and relaxations (also called “peristaltic waves”) that propel food along the esophagus. The peristaltic waves also prevent the bolus from rolling back.

Finally, at the end of the esophagus, the lower esophageal sphincter relaxes, allowing and regulating the passage of the bolus into the stomach.

Mixing the bolus with gastric juices in the stomach

Once the food is in the stomach, the gastric enteric reflexes are activated that become peristaltic movements of the muscular walls of the stomach, that is, in contraction and relaxation movements.

In this phase, these movements of the stomach are also called "mixing waves", since their primary function is to mix the food - food bolus - with stomach secretions or gastric juices.

Chyme is formed from this mixture, a semi-solid pasty mass made up of digested food.

After a few hours, when the entire bolus has been transformed into chyme, the mixing waves push the chyme through the pyloric sphincter located between the end of the stomach and the beginning of the small intestine.

In this way, the chyme does not leave the stomach in one go, but little by little, crossing the pyloric sphincter thanks to a repetitive back and forth movement generated by mixing movements.

The enterogastric reflex is a mechanism to prevent an excessive amount of chyme from entering the small intestine, and this can erode intestinal cells due to an exaggerated influx of gastric acid present in the chyme.

Nutrient absorption in the small and large intestines

Once the chyme enters the small intestine, another type of movement takes place in addition to the peristaltic movements that move food.

They are called "contractions or segmentation movements," and they are mixing movements that occur in the form of constrictions in the different sections of the small and large intestines. Its main function is to mix food to increase its absorption.

The segmentation contractions do not produce a unidirectional displacement of the chyme, but back and forth, which is why it may rather delay the passage of the chyme along the two intestines.

While the peristaltic movements that produce a single "forward" movement are rhythmic and occur in longitudinal muscles, segmentation movements occur in circular muscles located around the small and large intestines, so they are two different types of movements which take place in the last phase of digestion.

After the nutrients are absorbed thanks to the segmentation contractions, the peristaltic movements of this stage occur, called "migratory motility complexes", which move the chyme from the small intestine to the large intestine, and then from it to the rectum.

conclusion

In this way, it is concluded that in the general process of digestion a series of sub-processes are identified that are characterized only by being mechanical, that is, by only being in charge of the mechanical transformation of the food that we eat throughout all the phases of The digestion.

Within these mechanical processes, different muscles and sphincters work voluntarily and involuntarily, the latter responding to stimuli of hormonal and neurological origins.

In addition to the initial phase of crushing food, the only voluntary phase, there are two types of involuntary movements, which are "peristaltic" and "segmentation".

Peristaltic movements are different in each organ according to their nature, but they are characterized by rhythmic contractions and relaxations of different muscles, which produce a movement in a single direction that pushes food throughout the entire digestive system.

On the other hand, segmentation movements are only responsible for mixing food in the small and large intestines, facilitating the process of absorption of nutrients by making them come into contact with the mucosa in both intestines.

References

1. DÍAZ, E. (2005). Nutrition for educators. Retrieved August 23, 2017 on the World Wide Web: books.google.com.
2. HERNÁNDEZ, A. (2010). Nutrition Treatise / Nutrition Treatise: Physiological and Biochemical Basis of Nutrition / Physiological and Biochemical Basis of Nutrition. Retrieved August 23, 2017 on the World Wide Web: books.google.com.
3. John Wiley & Sons (2008). The Digestive System. Mechanical Digestion in the Gastroinestinal Tract. Retrieved August 24, 2017 on the World Wide Web: johnwiley.net.au.
4. Wikipedia The Free Encyclopedia. Retrieved August 23, 2017 on the World Wide Web: wikipedia.org.