Egestion is a physiological process in which undigested materials are expelled in the form of faeces.

In unicellular organisms, such as bacteria, it basically consists of the expulsion of unusable materials to the outside of the cell. In contrast, in the case of multicellular organisms, such as humans, food undergoes a longer process.

Many people confuse excretion with egestion and, although both are related to digestion, they are two different physiological processes.

Human digestion: definition and phases of this physiological process

Before going into more detail with the concept of egestion, it is necessary to understand how human digestion takes place and the processes that occur to food before it is eliminated in the form of faeces .

When we eat, food enters the digestive system. The main function of this apparatus is to process the food in order to obtain as many nutrients as possible from it and to eliminate what is not usable or has remained as waste.

A whole set of organs is involved in the process of digestion: mouth, salivary glands, esophagus, stomach, pancreas, liver, gallbladder, small and large intestines, appendix, rectum and anus.

The first place food passes through is the mouth. There it is chewed and mixed with the saliva, starting the digestion and beginning its decomposition. In this phase of the digestion the food is called alimentary bolus.

The bolus goes into the stomach through the esophagus and then into the small intestine, where further digestion takes place. As the food has been digested, the molecules that were present in it can be absorbed more easily.

These nutrients are introduced into the bloodstream, through which they will travel to all parts of the body where they are needed.

Not everything is absorbed in the small intestine. Only the smallest and most soluble substances can be absorbed through the walls of this organ. Those that are not, which are larger and insoluble, in case they have not been reduced in size by the action of enzymes, cannot be used . This is the phase prior to egestion.

What is egestion?

The part of the food that has not been able to be absorbed in the small intestine goes into the large intestine. There, the excess water is absorbed and through the action of bacteria what is left of the food is degraded .

The result of this is faeces, composed mostly of water and bacteria, plus substances that the human body cannot digest, such as cellulose and fibre. In addition to that which has not been used, the faeces contain substances that could be harmful to the body and that need to be removed.

Bacteria in the digestive system play a very important role for humans because they digest substances, such as certain types of carbohydrates, and synthesize proteins, such as B and K. They also fight other bacteria that could be harmful to the human body, which cause diseases and digestive problems.

Properly said, the process of egestion occurs when what has not been able to be used by the body is stored in the rectum . It is there that, when the signal is given, the waste is evacuated through the anus.

The output of the stool is controlled by the anal sphincter, which is made up of two parts: internal sphincter and external sphincter. If there is debris in the rectum, the anal sphincter is stretched and allows stool to come out.

Differences between egestion and excretion

Today, both in general culture and in some school books, these two terms are still confused. Although both are two phases present in digestion, they have certain nuances that differentiate them.

Egmanagement is the elimination of what came with the food and that has not been able to be used, such as non-digestible substances and harmful elements for the human body. It is basically the part of the food that has not been introduced into the bloodstream and used by the body, and is eliminated in the form of faeces.

On the other hand, excretion is a process in which what is eliminated are substances that have been used to maintain vital functions . The cells need energy to carry out their functions, and for this they need nutrients. These nutrients come in the form of organic molecules, which are broken down inside the cell and produce energy. The residues of this process leave the cell and are eliminated through the urine.

Associated problems

Whether due to illness or a poor diet, there can be problems in eliminating the stool .

These problems may not be serious and can be solved over time, however, if they persist, it is necessary to go to a professional to ensure that it is not the consequence of a larger problem.

1. Diarrhea

Diarrhea occurs when soft, watery stools are passed because they have been a short time in the small intestine.

It can be caused by contamination of food and water, viruses, parasites, drug use and abuse, food intolerance and sensitivity, stomach surgery, stomach diseases, and problems with colon function.

2. Fecal incontinence

It is the inability to control when to defecate . It may be the result of a loss of control of the sphincters or bowels, which requires going to a professional to help you learn how to control them again.

3. Constipation

It is difficult to eliminate the stool, which can be dry and very hard . Although being constipated does not mean not being able to have a bowel movement every day, it is considered constipation to do so less than 3 times a week.

4. Encopresis

Encopresis is the involuntary removal of stool at inappropriate places and times. This elimination disorder usually occurs in 4-year-old children and can lead to multiple causes. It usually occurs when retained stool builds up in the rectum and colon, causing swelling in the belly, loss of control of bowel movements, and even loss of appetite.

The child cannot control the passage of the stool, which can be both liquid and solid, or be large enough to block the toilet.

If the child has not previously learned to control the sphincters, we speak of primary encopresis. If the child has learned to control the sphincters before he or she suffers from encopresis, we talk about secondary encopresis. There may be emotional factors behind the child’s faecal incontinence, such as poor family dynamics.

Bibliographic references:

  • Keeton, W., and Harvey, D. (2016). Human digestive system. Encyclopedia Britannica.
  • Pocock, Gillian, (2006). Human Physiology (Third ed.). Oxford University Press.