Through digestion, ingested food is made usable for the body. Read more and the digestion time here!


Digestion is understood to mean the mechanical breakdown of the ingested food, its chemical breakdown by enzymes and their absorption into the blood (resorption). In this way, the body gains the necessary energy for life and building blocks for the organism. Read everything important about the digestion of man!

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  • How does the digestion work?

  • The fat digestion

  • The carbohydrate digestion

  • The protein digestion

  • How long does the digestion take?

  • What problems can digestion cause?

How does the digestion work?

Digestion begins as soon as solid or liquid food is taken into the mouth and ends with the elimination of indigestible remains of the chyme (feces, stool). The digestion time averages 33 to 43 hours, depending on the type of food.

Digestion in the mouth

The first stage of digestion begins in the mouth. Here, the food is mechanically minced with the teeth and mixed with the saliva from the three salivary glands (ear, Unterzungen- and Unterkiefers salivary gland). The saliva, which produces between 0.5 and 1.5 liters a day, already contains the first digestive enzymes (for example, ptyalin), which digest the chyme.

Tongue and cheeks form small portions from the shredded, undigested chyme, which are easy to swallow. In the esophagus, this porridge is transported by rhythmic contractions of the muscles in the stomach.

Digestion in the stomach

The upper part of the stomach first absorbs the incoming food like a reservoir and transports it to the lower part, where it is further crushed and mixed. The gastric juice, which is produced by glands of the gastric mucosa, contains hydrochloric acid enzymes for protein digestion.

Certain cells in the stomach wall (main cells) secrete pepsinogen - the inactive precursor of the digestive enzyme pepsin. It is activated by the acidic environment in the stomach, which is caused by hydrochloric acid. It is released from the parietal cells (parietal cells) into the interior of the stomach. In addition, these cells produce the "intrinsic factor," a glycoprotein that is needed in the small intestine for the absorption of vitamin B12 (cobalamin) into the blood.

In order that the aggressive gastric acid does not digest the stomach wall, it is covered by a protective layer of mucus. The mucus is produced by the so-called side cells in the stomach wall.

Digestion in the intestine

In the small intestine the food pulp is further mixed and split by enzymes. The fission products (simple sugars, fatty acids, glycerol, amino acids) as well as vitamins, minerals and water are absorbed into the colon in the blood. There are secretory secreting glands that secrete mucus or water and salts.

The fat digestion

Fat digestion starts in the mouth with the lipolytic enzyme lipase, which is contained in the saliva. It continues in the stomach, where the fats are emulsified by the motor function of the stomach wall and further decomposed by the lipase from the gastric juice.

The main part of the fat digestion but takes place in the small intestine: The small intestine wall releases the hormone cholecystokinin: It stimulates the pancreas (gland) and the gallbladder to secrete their secretions in the duodenum. The pancreatic juice contains lipolytic lipases. The bile consists among other things of bile acids, which are necessary for the fat digestion.

There are many organs in the abdomen. And all can cause pain. See here, when you have to take the complaints seriously.

The carbohydrate digestion

Carbohydrate digestion also starts in the mouth with the enzyme amylase. On the large scale, however, it only takes place in the small intestine (no carbohydrates are digested in the stomach): In the duodenum, the carbohydrates are decomposed by the pancreatic enzymes amylase, glucosidase and galactosidase.

The protein digestion

Protein digestion starts in the stomach using the enzyme pepsin. This is first released from the gastric wall as an inactive precursor (pepsinogen) and activated by the gastric acid.

In the small intestine, protein digestion continues. The responsible enzymes are derived from the pancreas: trypsin, chymotrypsin, elastase and the carboxypeptidases A and B. They too are first released as precursors and then activated in the gut.

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    What gut bacteria can do

    In the human intestine billions of little roommates cavort. There, they not only help with digestion. Intestinal bacteria affect the entire body to the brain and even control feelings. How do you do that?

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    Thick or thin?

    Normally, stretch receptors in the stomach and peptide messengers signal that you feel full after a decent meal. Some of the small roommates in the intestine work against it and produce certain messengers. These pretend to the body, one is still not full. So they provide enough food replenishment.If you have many of the hungry subtenants, you will get fat - and maybe even develop diabetes. But there are also slimming products in the gut.

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    Do not feel like sweets?

    The hunger artist among the intestinal inhabitants is the bacterium E. coli. It uses less food than other bacteria. When its human host eats little sweets, E. coli benefits because its hungrier competitors thrive so less well. E. colis trick: Since its cell wall consists of sugar, it suppresses the desire for sweets in its human host. This also benefits the slim line of the people.

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    Also with various allergies and autoimmune diseases, the intestinal bacteria seem to be related, such as with asthma. When they decompose fiber, they produce fatty acids, which are transported with the blood into the bone marrow. There they influence the production of certain immune cells. These then migrate to the lungs, where they slow down the excessive immune response typical of asthma.

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    Protection against influenza viruses?

    The influence on the immune system can also be a positive one: The intestinal dwellers are also a booster for the immune system. They strengthen the immune system in infections and combat influenza viruses and co. Vigorously. Experiments with mice show: If the intestinal microflora is missing or decimated, an infection is much more serious.

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    Healthy gut, healthy spirit?

    The power of intestinal bacteria probably reaches into the brain and affects the psyche. Recent studies suggest that an unfavorable composition of the intestinal flora could promote depression, schizophrenia and possibly even dementia. One possible reason: Bacteria in the intestine produce fatty acids during digestion that activate the garbage collection in the brain. If it does not work properly, the nerve cells in the brain can be damaged.

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    Even as we feel, the bacteria in our guts are interfering. Certain lactic acid bacteria, for example, produce a precursor to the happiness hormone serotonin and could thus lighten the mood.

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    ... or Griesgram?

    Other microbes could also spoil the mood. For example, cry children have altered gut flora. The scientists' hypothesis: The intestinal bacteria spur children's displeasure so that they are fed more. And that also benefits the bacteria.

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    Hero or scaredy cat?

    An experiment with mice has shown that gut colonies may even influence how anxious someone is. Rodent-free rodents were either given intestinal bacteria by anxious or courageous animals. The amazing thing is that they behave accordingly more anxiously or courageously. It even worked to "reprogram" the animals. Previously anxious mice became courageous rodents with the microbiome.

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    Exchanged subtenants

    That it can give bad belly rumble, if the intestinal flora is disturbed, comes to light. Then threaten complaints from irritable bowel syndrome to severe inflammatory bowel disease. By contrast, a drastic method helps: The rioting subtenants are eradicated with antibiotics. Then the patient receives new subtenants - in the form of a chair transplant with feces from a healthy person.

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    Casting for the intestinal WG

    With so much impact on health, of course, the question arises: Can one choose his Darmmitbewohner? And who would you like to live in your Darm-WG? Basically, the more colorful the shared flat, the better. In fact, you can influence your roommates through your diet. The rule is: fat and high-sugar food limit the variety in the intestine, fiber increases it.

How long does the digestion take?

Ingested food stays in the stomach for about one to three hours. In the small intestine, the average length of stay is seven to nine hours, in the large intestine 25 to 30 hours. It can sometimes take a lot longer for the indigestible remnants to be excreted as stool: the length of stay in the rectum is between 30 and 120 hours.

What problems can digestion cause?

Digestion may be disturbed due to different causes. For example, gastrointestinal influenza (gastroenteritis) triggers diarrhea and vomiting.

The irritable bowel syndrome (irritable bowel syndrome) is accompanied by abdominal cramps, bloating, diarrhea or constipation.

Food intolerance (intolerance) affects the digestion of a particular nutrient. So the body can not properly use the milk sugar due to an enzyme deficiency in the small intestine with lactose intolerance.

In celiac disease (gluten intolerance) is the digestion disturbed by grain: the body does not tolerate the protein contained gluten. The small intestinal mucous membrane is damaged, which also affects the absorption of other nutrients.

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