Home Anatomy Gut (Gastrointestinal tract): structure and function

Gut (Gastrointestinal tract): structure and function

by Josephine Andrews
Published: Last Updated on 320 views

The gut is the part of the alimentary canal where food, after being broken up and digested in the mouth and stomach, is further digested. The resulting small building blocks of nutrients (such as simple sugars, fatty acids, amino acids) are absorbed into the blood. Substances that cannot be used are excreted as stool (faeces). Read everything you need to know about the gut: anatomy, function and important diseases!

What is the gut?

The intestine is the main part of the digestive system. It starts at the pylorus (stomach pylorus), leads to the anus (anus) and is divided into the slimmer small and the wider large intestine. Both, in turn, have several sections.

small intestine

It is divided from top to bottom into the duodenum, jejunum and ileum. You can read more about this in the article Small intestine .


It is divided from top to bottom into the sections appendix (with appendix), large intestine (colon) and rectum or rectum (rectum with anus). Read more about this in the Colon article .

How long is the intestine in total?

The total length of the intestine is about eight meters. Five to six meters of this is in the small intestine and the rest in the large intestine.

What is the function of the intestine?

The meter-long alimentary canal not only ensures the chemical breakdown of food, the absorption of the food components in the body (absorption) and the excretion of the food residues through the anus. It also represents a barrier for pathogens and plays an important role in regulating the water balance: the intestines can absorb and also excrete large amounts of liquid.

small intestine function

The large digestive glands open into the duodenum (duodenum): the liver, whose secretion (called bile) can be temporarily stored in the gallbladder, and the pancreas (pancreas). Both digestive secretions contain important digestive enzymes for the chemical breakdown of carbohydrates , fats and proteins.

Additional glandular secretions originating from the intestinal wall itself participate in digestion. After the food has been broken down and digested in the mouth and stomach, the food components are broken down into small components throughout the small intestine and absorbed into the blood (absorbed):

Carbohydrates are broken down into simple sugars (monosaccharides), proteins into the individual amino acids , and fats into glycerine and free fatty acids. After being absorbed into the blood, these nutrients are first transported to the liver via the portal vein. It is the central metabolic organ.

Other substances are also absorbed in the body in this way, such as vitamins and minerals.

colon function

The food components that the body does not need or cannot use reach the large intestine. The muscle wall pushes this pulp with wave-like (peristaltic) movements through the individual sections to the exit (anus). On its way, the stool (faeces) is thickened by dehydration. Mucus secreted by the intestinal wall makes it slippery.

Countless bacteria of more than 400 different species naturally live in the large intestine. Their total number is estimated at around ten trillion, and their total weight at around 1.5 kilos. They process the indigestible leftover food. They also produce substances that the body can use in part (some B vitamins, vitamin K ).

The work of the intestinal bacteria also produces gases and substances that give the thickened food pulp its color and smell. This faeces, which can no longer be used, is ultimately transported to the outside via the anus.

Depending on the type of food consumed, it takes 33 to 43 hours from ingestion to defecation.

Where is the gut?

It fills almost the entire abdominal cavity below the stomach. The duodenum is in the upper abdomen just below the stomach, the jejunum is on the top left and the ileum is on the bottom right. The numerous loops of jejunum and ileum are collectively referred to as a convolute. It is to a certain extent framed by the colon. This then opens out below with the rectum and anus.

What problems can the intestines cause?

In the case of a duodenal ulcer (Ulcus duodeni) , a more or less large area of ​​the mucous membrane in the duodenum is damaged. A gastric ulcer (Ulcus ventriculi) often occurs as well. Men are affected more frequently than women. In most cases, the cause of the ulcer is an infection with the “stomach germ” Helicobacter pylori.

An irritable bowel (colon irritabile) manifests itself in chronic symptoms such as diarrhea and/or constipation, flatulence and abdominal pain. An organic cause for this cannot be determined. The disease mainly affects women.

A “gastrointestinal flu” is an inflammation of the mucous membrane in the digestive tract caused by pathogens, which can lead to diarrhea and vomiting.

Crohn’s disease and ulcerative colitis are chronic inflammatory bowel diseases (IBD). Crohn’s disease can affect the entire digestive tract (from the oral cavity to the anus). The inflammatory process in ulcerative colitis usually begins in the rectum and spreads to the colon.

In people who suffer from hemorrhoids, a vascular cushion in the anal canal is abnormally dilated. Possible symptoms are, for example, bright red traces of blood on the stool or toilet paper, pressure pain, burning or itching in the anus. In advanced stages, the stool can no longer be held back. Risk factors for hemorrhoids include repetitive straining during bowel movements, a low-fiber diet, pregnancy and weak connective tissue.

Diverticula are outward protrusions of the intestinal wall. If several diverticula form side by side, physicians refer to this as diverticulosis . The protuberances can become inflamed ( diverticulitis ). Sometimes they also burst, and the inflammation can then spread to the peritoneum. Diverticulitis is treated with antibiotics. Sometimes the inflamed diverticula have to be surgically removed.

Intestinal polyps are protrusions of the mucous membrane that form primarily in the colon and rectum – usually without any apparent cause. They often do not cause any symptoms, but should still be removed because they can degenerate and lead to colon cancer. This form of cancer is widespread. The malignant tumor usually forms in the intestine in the last two sections of the intestine: colon (colon carcinoma) or rectum (rectal carcinoma).

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