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The large intestine (Latin intestinum crassum) is the last part of the digestive system. This is where undigested food remains are formed into feces and then discharged to the outside. But it is not everything. The large intestine has other, very important functions. It is here that microorganisms live, which produce vitamins, but also take care of the good condition of the whole organism. Find out how the large intestine is built and what exactly the processes take place in it.

Large intestine(Latinintestinum crassum ) this is the end section of the digestive tract, 1.3 to 1.5 m long. You could say that it surrounds the abdominal cavity, so if we feel any movement, e.g. gas shifting, on the right or left side of the abdomen, it is in the large intestine.

Structure of the large intestine

The connection of the small and large intestines is called the ileocecal valve (also known as the Bauhin valve). Immediately after it begins the large intestine.

Its first section, and the thickest at the same time - it may be 8 cm in diameter at the moment of diastole - is the contra-angle.

There is also an appendix (so-called blind bowel - an organ measuring 8-10 cm, lying in the right lower abdomen).

It is commonly referred to as a vestigial organ, but it is not as redundant as it was until recently believed, although, indeed, you can live after an appendectomy.

However, it is worth knowing that it is made of lymphoid tissue, like tonsils, which is why it is sometimes called the intestinal tonsil, and plays an important role in the immune system.

Like tonsils, it collects various types of waste, incl. captures dangerous bacteria, so it is a kind of bacterial filter in the body.

In addition, it is a warehouse of the so-called beneficial bacteria, and also produces white blood cells that protect the body against harmful viruses and bacteria.

Further behind the cecum, another segment of the large intestine called the colon begins. The first part is the ascendant. It runs up the right side of the abdomen towards the liver.

This is where it bends and the next part of it, running horizontally, is called the cross member. However, when it does turn again, this time down the left side of the abdomen, it is called the descendant. It ends with a sigmoid, which is about 15 cm long and runs along the sacrum.

Next is just the rectumand anus, i.e. the end of the digestive system and at the same time the gate to the external environment. There is a very important muscle in the anus called the sphincter, which allows us to control bowel movements and stop the stool in case of need.

Along the colon, from the appendix to the rectum, run three strips of the colon - free, mesenteric, and net - made of muscle tissue. They are shorter than the large intestine by about 1/6 and therefore cause its folding.

This structure of the intestines causes, inter alia, that the water from the intestinal contents is drained as much as possible (squeezing and relaxing).

The colon wall no longer has intestinal villi like the wall of the small intestine. However, it is made of four layers. They are:

  • serous membrane
  • proper muscle membrane responsible for the contractile activity of the intestinal wall
  • submucosa
  • mucosa covered with a cylindrical epithelium composed of goblet cells that secrete mucus

The large intestine is highly vascularized. The arterial blood is supplied here with the help of two arteries - the upper mesenteric and the lower mesenteric arteries.

The upper vasculature of the transverse colon, ascending colon and Bauhin's valve area, and the lower descending colon and upper rectum.

The rest of the rectum is vascularized by the middle rectal artery departing from the internal iliac artery and the inferior rectal artery departing from the internal vulvar artery. The venous system corresponds to the arterial system.

What is happening in the large intestine?

In this part of the digestive system, undigested food remains are formed into feces, which is facilitated by perist altic movements of the intestines, but also water reabsorption takes place.

The large intestine is able to recover up to 90% of the water contained in the digestive content that reaches it. This is why the content of the (normal) stool is compact and quite hard, unlike the fluid content of the small intestine.

In addition to water from the large intestine, the body is still able to recover some electrolytes and mineral s alts. On average, it is from 1 to 2 liters of fluid a day and about 200mEq of sodium and chlorine.

However, processes such as digestion and absorption practically do not take place in this section.

However, intestinal bacteria live here, among which the predominant anaerobes of the genusBacteroides fragilisandClostridiumsp. The main aerobic bacterium is Escherichia coli .

Bacteria play an extremely important role in the intestine, which we are only starting to find out about in recent years.

Worth knowing

Peristalsis is the so-called bowel movements. The greater the mobility of the intestine, the more efficiently the defecation process takes place. However, it is not good when it is too big.

Peristalsis is regulated by hormones such as cholecystokinin, motilin and catecholamines, but also by emotional factors, such as stress (catecholamine is also called the stress hormone).

This is why when we are nervous about something, e.g. an exam, we run to the toilet more often, and when we experience chronic stress, we may suffer from constipation.

Irritable bowel syndrome, a typically emotional disease, consists of peristalsis disorders - periodic diarrhea and constipation.

What bacteria are in the large intestine?

Microorganisms with a total mass of 1.5-2 kg, inhabiting the large intestine, are responsible for the production of vitamins B and K, they also break down proteins - it is the products of their decomposition that give us the smell of the stool.

They also conduct fermentation, which contributes to the formation of a kind of gel that softens the stool and facilitates its passage through the digestive tract.

Bacteria also have protective functions. They prevent the growth of potentially harmful microorganisms that could lead to the formation of some infectious diseases.

The total number of microorganisms that live in the gut is called the microbiota or the microbiome, the latter being more related to their genes. The number of these microorganisms exceeds the number of cells in the human body!

Sometimes they are even referred to as an additional organ, but the composition of the microbiota of each person is different, as unique as fingerprints.

A baby in the womb has a completely sterile digestive tract. It fills up with microorganisms gradually, to reach a state comparable to that of an adult in the second year of life.

The variability of the microbiota depends on age, but also on sex, genes and environmental conditions. For example, any previous antibiotic therapy seriously disturbs its composition, so it is important to remember about a diet rich in natural probiotics, such as pickled vegetables, beet leaven or fermented milk drinks.

There is a close relationship between the composition of the microbiota and the occurrence of various diseases. Abnormal intestinal bacterial flora disrupts the functioning of the entire digestive system, but not only.

It is also believed to cause allergies, type 2 diabetes, obesity, cancer, autism and mental he alth problems. After all, if strong emotions can lead to diarrhea, why shouldn't this relationship also run inreverse?

Defecation, i.e. the end of the large intestine

Faecal excretion is regulated by a number of factors, the most important of which are: intestinal perist altic activity, emotions, quantity, quality and volume of meals consumed.

The rectum is usually empty. However, when the stool mass shifts into this area, for example, caused by eating another meal, the rectum expands - with simultaneous tightening of the anal sphincters.

The person then feels the pressure and strives to defecate. Since it can control the work of these muscles, the act of defecating is not spontaneous. Under the right conditions, the muscles of the rectal sphincter relax and the stool is expelled.

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Category:

Gastrology