The 12 parts of the digestive system (characteristics and functions)

The digestive system is made up of organs and tissues that, working in a coordinated way, allow the degradation of food into simple molecules that can be assimilated by our cells.

As we well know, every living being performs three vital functions: reproduction, relationship and nutrition. And this nutrition is the set of physiological processes that allow the body to obtain both the matter and the energy necessary to stay alive and functional.

There are many forms of nutrition in nature, from that of animals to the photosynthesis of plants, passing through bacteria that feed on inorganic substances present in hydrothermal sources or fungi that feed on decomposing organic matter.

And the human being, a highly evolved organism in all senses, also has a set of organs and tissues that, despite being different, allow the macronutrients present in food to be degraded until we obtain molecules that can be assimilated by our cells and from which we can obtain the matter to build our body and the energy necessary to live .

We are talking about the digestive system. And in today’s article, in addition to perfectly understanding what functions it performs as a whole, we will analyze what structures it is made up of and what is the specific role of each of them. Let’s go there.

What is the digestive system?

The digestive system is one of the thirteen systems of the human body and, as such, is born from the union of organs and tissues that, despite being different in terms of morphology and physiology, work in a coordinated way to, in this case, allow the digestion of food .

In other words, the digestive system is responsible for capturing food, breaking down macronutrients into simpler molecules that are already bio-assimilable, and subsequently allowing their absorption into the bloodstream so that these nutrients reach our cells, where they will be used to obtain both matter to build organs and energy to keep us alive and in good health.

The digestive system, therefore, is the only structure in our body capable of providing us with the necessary nutrients so that the rest of the body’s systems remain functional. And it is that he is only in charge of maintaining the vital function of nutrition .

Unfortunately, the fact that they introduce products from the environment also makes them susceptible to all kinds of diseases. In fact, gastrointestinal pathologies are among those with the highest incidence worldwide and, in underdeveloped countries, they are the main cause of infant mortality.

In short, the digestive system is the set of different organs and tissues that, as a whole, are involved in swallowing, digestion and absorption of nutrients . But what structures is it formed by exactly? This is what we will analyze next.

What is the anatomy of the digestive system?

As we have been commenting, the digestive system is in charge of swallowing, digestion and the absorption of nutrients. And all the organs that have a role in any of these functions will be part of this system.

In this sense, the digestive system is made up of the following structures: mouth, tongue, salivary glands, pharynx, esophagus, stomach, liver, pancreas, small intestine, large intestine, rectum, and anal canal . Let us see, then, the anatomy and the functions of each one of them.


The mouth is an organ that belongs to the digestive system and, in fact, it is the natural opening of our body that marks the beginning of this system. Located in the lower part of the face and oval in shape, the mouth is endowed with voluntary movement thanks to different muscles and joints that allow chewing.

That is to say, digestion begins thanks to the mechanical action of the mouth , since jaw movements, together with the presence of healthy and strong bones and the secretion of saliva, the food bolus begins to be crushed to facilitate the action


The tongue is a sensory organ since the taste buds that allow the sense of taste are located on it, but it also belongs to the digestive system. With a muscular nature, a cone shape and a length of about 10 centimeters, the tongue works together with the mouth when it comes to starting the digestion of food.

As far as digestive role is concerned, the tongue has the very important function of removing the food bolus inside the oral cavity and allowing a correct grinding of the food, as well as an adequate mix between the food and the enzymes present in the saliva.

Salivary glands

The salivary glands are also organs that belong to the digestive system and that, in fact, are of paramount importance in the first phase of digestion that takes place in the mouth. These are structures located in different regions of the oral cavity whose function is to synthesize and release saliva.

Saliva is essential as it keeps the mouth moist, serves as a conductive medium for the sense of taste and contains antimicrobial substances to prevent the proliferation of bacteria in the oral cavity, but it is also vital for digestion.

And it is that in this saliva there are digestive enzymes that, when mixed with the food bolus, allow the degradation of complex molecules into simpler ones . Some of these are only present in saliva, so if this first digestion is not carried out properly in the mouth, it cannot be recovered anywhere else.


The pharynx is an organ that, although it is part of the digestive system, is also a structure of the respiratory system. We are talking about a duct located in the neck that, as far as digestive role is concerned, connects the mouth with the esophagus.

Therefore, within this system, the pharynx has the function of leading the partially digested food bolus from the mouth to the esophagus , the structure that, finally, will lead it to the stomach.

Be that as it may, it is a tubular organ of a muscular nature (in order to be able to adapt to the food bolus and allow it to descend properly without causing obstructions) of about 15 centimeters in length and a diameter of between 2 and 5 centimeters.


The esophagus is an organ that is only part of the digestive system, that is, it no longer has the function of conducting air like the pharynx; just the food bolus. In this sense, the esophagus is also a conduit of a muscular nature that arises as an extension of the pharynx and has the function of driving food to the stomach.

It is located behind the trachea and consists of a muscular tube with an average length in adults of between 22 and 25 centimeters that leads the food bolus from the pharynx to the lower esophageal sphincter or cardia, which is the point of union between the esophagus and the stomach. This sphincter is a circular muscle that opens when food arrives, thus allowing contents traveling down the esophagus to spill into the stomach


The stomach is the center of the digestive system. It is an organ with a length of about 20 centimeters, a “J” shape and a volume at rest of about 75 milliliters, although thanks to its muscle fibers, as it fills with food, it can expand to a volume of more than 1 litre.

In the walls of the stomach there are different cells that produce both digestive enzymes and hydrochloric acid , an extremely acidic compound that, in addition to killing virtually all germs that may have entered through food (unless they have resistance structures) Helps solid foods turn into liquids.

In this sense, the stomach is an organ inside which different involuntary muscular movements take place that allow the mixing of the food bolus with the digestive enzymes (they break down the macronutrients into simple molecules that are already assimilable) and the hydrochloric acid (allows the solids to let’s go to a liquid).

After between 1 and 6 hours of digestion, the solid food bolus has become what is known as chyme , a liquid where the molecules are structurally simple to be absorbed in the intestines. We have managed to degrade solid foods until they become a liquid where the solid particles are less than 0.30 millimeters in size.

After the generation of chyme, it must continue its journey to the intestines. For this reason, what is known as the pyloric sphincter opens, a circular muscle that, when it is time, allows the passage of chyme towards the small intestine.


Before we get to the intestines, we have to stop at two very important structures. The first of these is the liver. It is the largest organ in the human body (not counting the skin) and is part of the digestive system, although it performs functions that go far beyond the mere digestion of food.

It is located in the upper right part of the abdominal cavity, above the stomach and just below the diaphragm. It has a weight of 1.5 kg and a length of 26 centimeters, which makes it the largest internal organ.

As far as digestive role is concerned, it has the very important function of producing bile , a substance that, when necessary, is poured into the duodenum, which is the initial part of the small intestine. Once there, the bile helps the body digest fats, something the stomach is not fully capable of.

But beyond this, the liver is essential for the purification of drugs, alcohol and other toxic substances from the blood, the storage of glucose for retention or release depending on blood levels, the conversion of ammonia into urea (and so the kidneys can synthesize urine), the production of immune factors to stimulate defenses against infections, the synthesis of “good” cholesterol, the storage of iron, etc.


The pancreas is an organ that belongs to both the digestive and endocrine systems, because in addition to helping digest food, it produces vital hormones for the body, among which insulin stands out, the one that regulates blood glucose levels.

But as far as digestive role is concerned, the pancreas is still very important. It is an organ with an elongated shape, a length of between 15 and 20 cm, a thickness of between 4 and 5 cm and a weight that ranges between 70 and 150 gr.

Similar to the liver, it secretes its contents into the duodenum, which is the initial portion of the small intestine. But in this case, it does not synthesize and release bile, but what is known as pancreatic juice, a liquid that contains both digestive enzymes to continue the digestion of carbohydrates, fats, and proteins, as well as bicarbonate, something essential to neutralize the acids that come from the stomach . That is, it neutralizes the acidity so that the intestines are not damaged by hydrochloric acid.

Small intestine

Now we come to the final part of the digestive system: the intestines. The small intestine is an elongated organ with a length of between 6 and 7 meters. Its function is, after receiving the chyme from the stomach, to continue the digestion of carbohydrates, proteins and fats thanks to the bile and pancreatic juices and, especially, to carry out the absorption of nutrients .

In fact, practically all the absorption of the molecules takes place in the small intestine, which has many villi that, in addition to increasing the contact surface, allow the passage of nutrients to the blood circulation, since their size allows it. Once there, the blood will distribute these nutrients throughout the body.

Large intestine

The large intestine is an organ with a length of about 1.5 meters that consists of an extension of the small intestine, with which it communicates through what is known as the ileocecal orifice. It is located in front of the small intestine, surrounding it.

Be that as it may, when the chyme arrives here, practically all the nutrients have already been absorbed, so the function of the large intestine is different. In this case, this organ is responsible for absorbing water, transforming this liquid chyme into a solid residue from which no more nutrients can be obtained. That is, its function is to form and compact the stool .

In parallel, the large intestine houses most of the intestinal flora. Inside, millions of bacteria of thousands of different species create populations that, far from causing us harm, enhance our gastrointestinal health and help both the absorption of the last nutrients and the reabsorption of water.


The rectum is the final portion of the large intestine. It is a region with a length of about 12 centimeters and a sack shape with the function of accumulating feces . When it reaches the rectum, no more water can be absorbed, so new ones are no longer formed.

Therefore, the feces accumulate in the rectum until an amount is reached that stimulates the need to defecate. At that time, voluntary muscle movements allow the exit of feces from the large intestine towards the anal canal.

Anal canal

The anal canal is the final part of the digestive system. As in the previous structure, neither digestion nor absorption of water takes place, so they are really part of the excretory system. Be that as it may, it is a conduit about 4 centimeters long that is already outside the abdominal cavity.

Its function is to transport feces to the outside , since the anal canal, in its terminal part, communicates with the environment through the anus, the hole through which the feces produced in the large intestine are released, thus ending the trip. throughout the digestive system.

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