Digestion: how does it happen? What are digestive enzymes?

Our body is composed of several cells, tissues and organs that together form some systems that perform essential functions for our survival. One of them is the digestive system, which acts on the disintegration and absorption of nutrients from the foods we eat daily.

Read on to learn more about how this system works and what are the fundamental steps for this process to occur in our body.


What is digestion and how important is it for our organism?

Food is a source of numerous nutrients, which are only absorbed and used by the body due to the digestion process.

Digestion is the name given to the process of physical and chemical disintegration of organic foods so that they are absorbed by our body, ensuring the proper functioning of the whole body.

This process is done throughout the digestive system, which starts at the mouth during chewing, passing through the stomach, which causes a greater breakdown of food particles, going to the small intestine, where complete absorption of nutrients occurs.

In all, the bodies that make up this system are:

  • Mouth: considered the gateway, the mouth is formed by the lips, teeth (essential for chewing) and tongue (important for the perception of flavors and swallowing). It is in the mouth that the first breakdown of food occurs, so that they are swallowed and move on to the next stage of digestion.
  • Pharynx: common to the digestive and respiratory system, the pharynx is a mucosa through which the bolus (name given to food after chewing) passes to reach the esophagus and, soon after, to the stomach. This stage is called swallowing (swallowing).
  • Esophagus: tube that connects the pharynx and stomach, the esophagus has the function of pushing, through movements called peristaltics, the food bolus so that it accesses the stomach.
  • Stomach: located below the diaphragm, the stomach is responsible for the chemical digestion of the bolus, since within this organ an acidic substance (gastric juice) is released which breaks down the bolus into particles.
  • Small intestine: 6 meters long and divided into 3 portions (duodenum, jejunum and ileum), the small intestine is the longest part of the digestive system. It has the function of completely absorbing the nutrients of the chyme (name of the bolus after the action of gastric juice in the stomach).
  • Large intestine: representing the final stage of digestion, the large intestine (divided into cecum, colon, rectum and anus) measures around 15 cm, and has the function of absorbing water from the chyme, transforming it into fecal cake, which will be eliminated by the anus.

If any of these organs does not function properly, chances are that the digestion process will not operate properly, compromising the absorption of nutrients and elimination of waste (feces).

Therefore, it is important to consult a doctor when you notice frequent symptoms such as loss of appetite, heartburn , diarrhea , constipation , weight loss or weight gain quickly, as well as tiredness and other symptoms.

Mechanical digestion

Mechanical digestion refers to the stages in which the movements act on the ingested food, either to modify it or to move it to another stage. Thus, the entire digestive process suffered by food that does not involve chemical substances , is part of mechanical digestion.

Examples include:

  •  The crushing of food in the mouth by means of teeth and saliva, the movement (swallowing) performed to move the food along the pharynx and esophagus so that it reaches the stomach;
  • The contraction and relaxation (called peristaltic movements) of the muscles to ensure that the food moves forward to the next stage of digestion.

Chemical digestion

Chemical digestion, as the name implies, involves the involvement of chemicals in the digestion process when food reaches the stomach.

These substances are known as digestive enzymes, which are the proteins present throughout the digestive tract that act in the breakdown of different macromoleculars that make up the foods we eat daily. The main ones are:

  • Amylase (starch)
  • DPP-IV (casein and gluten)
  • Alpha Galactosidase (carbohydrates)
  • Xylanase: (hemicelluloses)
  • Lactase (lactose)
  • Cellulase (cellulose insoluble fiber)
  • Bromelain (proteins)
  • Pectinase (pectin)
  • Maltase (maltose)
  • Lipase (lipids)
  • Invertase (sucrose)
  • Hemicellulase (hemicelluloses)
  • Glycoamylase (starch)
  • Protease (proteins)

Digestive enzymes are produced naturally by the body, however, they can be supplied to the body through supplements that help to balance the proper amount.

Therefore, when the chemical digestion process is taking place very slowly, a specialist doctor can indicate the consumption of supplements with these substances to speed up digestion.

How does the digestion process take place?

Although the foods consumed daily go through the same system to be digested and absorbed by the body, there are differences in the form in which each element will undergo this process. So, see how the digestion of carbohydrates , proteins and lipids (fats) occurs :

Carbohydrate digestion

Carbohydrates, also called sugars, are a group of molecules very important for the supply of energy to the body, which is why they are present in abundance in nature.

In general, carbohydrates can be classified in two ways, simple and complex, which vary according to the time used by the body to digest and absorb the molecules of each one.

Therefore, if the digestion and absorption process is fast, it is a simple carbohydrate (sweets, candies, honey), however, if it is slower, it is a complex carbohydrate (whole bread and pasta, beans).

On average, the carbohydrate molecules most present in the diet are starch ( potatoes , rice, wheat), sucrose (table sugar) and lactose (milk sugar), which are directed and absorbed through a chemical process called hydrolysis (breaking of molecules into smaller particles in the presence of water).

This action occurs throughout the digestive system, with the aid of digestive enzymes such as salivary amylase (which acts during the chewing process) and pancreatic amylase (which acts in the small intestine, specifically in the duodenum).

At the end of the process, only glucose molecules remain, which are transported through the bloodstream and penetrate the cells to assist in the cellular respiration process.

Digestion of proteins

Formed from chains of amino acids, proteins are involved in essential activities for the body, such as muscle repair and the composition of cells, tissues and hormones.

The protein digestion process begins in the mouth, through the chewing of foods that contain this nutrient, such as eggs and meat.

After this phase, when the proteins go to the stomach, they find there the presence of hydrochloric acid (liquid secreted by the stomach), which quickly begins to “attack” the proteins, removing their hydrogen molecules.

This process ends up facilitating the performance of digestive enzymes under the proteins, causing them to be broken down into even smaller particles, and can then advance to the small intestine.

Once there, pancreatic enzymes (trypsin, chymotrypsin, elastase and carboxypolipeptidase) are released, performing, once again, a separation of molecules, leaving only peptides and amino acids, which are absorbed and transported to the liver.

From there, the amino acids are directed to different regions of the body, to participate in structural and metabolic processes.

Digestion of lipids

Lipids are molecules with great energy value that do not dissolve in water, but in substances such as alcohol, ether and acetone.

The lipid digestion process begins during chewing, since the consumption of high-fat foods stimulates the release of enzymes, called lingual lipases, which are present in glands below the tongue.

When forwarded to the stomach, the food cake composed of lipids passes through the second stage of digestion, which occurs through the action of gastric lipases, breaking down the fat into smaller particles.

However, due to the PH (index that shows the acidity) being extremely high, the lipids end up not being completely dissolved, being necessary that the small intestine finish this task.

In the small intestine, precisely in the bolus (which at this point is very acidic) stimulates the release of a digestive hormone called cholecystokinin. This hormone, in turn, causes the gallbladder to contract (which releases bile into the duodenum) and also pancreatic juice.

To finish the process, the lipids present in the bolus are emulsified by the action of bile salts (which form the bile), generating components that undergo a last stage of digestion by pancreatic lipase.

Soon after that, lipids release fatty acids, which are absorbed by the body and will join with other molecules, being useful for different metabolic activities, such as energy production, transport of accumulated fats in the liver to other tissues and adequate growth. of the cells.

What types of digestion occur in the mouth?

In the mouth, both mechanical and chemical digestion occur , since there is the grinding of the food consumed by the action of the teeth and the action of the enzyme salivary amylase (or ptialina) in the process, which facilitates chewing and disintegration of the food.

On average, a person produces 1 to 2 liters of saliva daily, which may increase according to the amount of food eaten.

In addition to the digestive function, saliva plays a protective role, since some infectious agents that try to invade the organism through the mouth are prevented by the action of immunoglobulin A (IgA), a protein present in the composition of saliva.

What can cause poor digestion?

Poor digestion can occur due to some food that was not well accepted by the body.

In general, poor digestion occurs due to inappropriate habits or excessive consumption of food that hinder some stage of the digestive process . Like, for example, chewing food quickly, drinking plenty of fluids during meals, eating foods high in fat and consuming caffeine in an exaggerated way.