What kind of response is food digestion

The digestive system

The human digestive system (gastrointestinal tract) enables the body to be supplied with energy and nutrients. The food supplied passes through the mouth, esophagus, stomach, small intestine and large intestine before it is excreted in the form of stool via the rectum. Other organs are also involved in the process of digestion. These include the pancreas, gallbladder and liver.

Food can only be used by the organism when it is broken down in the gastrointestinal tract. This requires a multitude of physical and chemical processes that are subordinate to both humoral - affecting body fluids - and neural - regulating mechanisms that belong to the nervous system. The bacteria in the intestinal flora play a particularly important role in the digestive system.

First station: the mouth

The mechanical grinding of the food takes place in the mouth. Mixed with saliva, it creates a swallowable pulp. Saliva production is a reflex triggered by the smell, taste and appearance of food. In addition, the salivary glands produce more of this useful fluid through chewing movements and mechanical irritation of the oral mucosa. How much saliva is released also depends on the fluid balance, i.e. the body's current "water supply".

The many small glands in the oral mucosa produce 1–1.5 liters of saliva per day. An important component of this is, for example, the substance ptyalin, a so-called alpha-amylase. Ptyalin starts digesting carbohydrates in the mouth. The basic tongue lipase, which is also found in saliva, prepares the dietary fats (triglycerides) for digestion in the stomach. Last but not least, the saliva also contains disinfecting substances such as fluoride or rhodanide ions.

Intermediate station: esophagus

The elevations on the tongue, the papillae, help to move the food between the rows of teeth and convey the cheeses in the direction of the esophagus. The soft palate and larynx serve as "guards": They ensure that the food does not get into the nasopharynx or the windpipe, but rather finds its way into the esophagus. The process of swallowing is a mechanism that should not be deliberately outwitted, for example by pouring down a drink without swallowing it. There is a risk of suffocation, as food or liquid can get into the windpipe.

The wave-like transport of food from the esophagus to the stomach is also a reflex. When the porridge arrives at the bottom, the "gate" to the stomach opens. These are smooth muscles arranged in a ring and located between the esophagus and antrum of the stomach. After the food has completely reached the stomach, these muscles close the stomach entrance again so that the stomach acid cannot irritate the sensitive surface of the esophagus.

+++ More on the topic: Reflux disease +++

Second stop: the stomach

In the stomach, the food mixture is mixed with the gastric juice through peristaltic (= wave-like) movements.

The gastric juice is produced by the glands in the lining of the stomach (gastric mucosa). Each gland contains different types of cells, each of which has different functions. The main cells produce pepsinogens, a precursor of the protein-splitting enzyme pepsin. Pepsin is needed to digest protein from food. The side cells make mucin, a mucus that protects the stomach from digesting itself. In addition, the secondary cells are involved in the breakdown of fats. The parietal cells produce the hydrochloric acid, which stabilizes the pH of the gastric juice between 2 and 4. Among other things, this keeps potentially pathogenic germs at bay. The parietal cells also play an important role in the absorption of vitamin B12. The gastric juice production is controlled by the hormone gastrin.

+++ More on the topic: Vitamin B12 +++

The chyme stays in the stomach for one to six hours, depending on the fat content. If the food is sufficiently decomposed, the stomach constricts in a ring and pushes the food with wave movements (= peristalsis) to the gatekeeper at the lower end of the stomach. This only lets through as much food as the small intestine can digest.

Third station: the small intestine

The small intestine (consisting of the duodenum, jejunum and ileum) is up to 5 meters long. 10–40 intestinal villi are lined up on a square millimeter of intestinal wall. The intestinal wall is traversed by a fine network of blood vessels through which all the nutrients absorbed by the villi enter the bloodstream.

When the food reaches the small intestine, the pancreas and liver also come into action. The pancreas releases enzymes and alkaline juices, two liters of which the organ produces every day. The liver stimulates the contraction of the gallbladder and the production of yellow bile. This happens more often with fatty foods.

Fourth station: the colon

The large intestine now takes on the decomposition of difficult-to-digest plant substances. These - e.g. cellulose - are broken down by bacteria. The totality of all microorganisms resident in the large intestine is called the intestinal flora. The nutrition-dependent bacterial flora also plays a role in the synthesis of the vitamins biotin, folic acid, vitamin K and niacin.

The intestinal wall absorbs food and water. This is how the thickening of the stool occurs. In addition, mucus is added to the excrement so that it achieves a certain lubricity. The so-called goblet cells are responsible for the production of mucus.

+++ More on the topic: The intestinal flora +++

The surface of the large intestine is not enlarged by villi like that of the small intestine; instead, it has bulges and wall reinforcements. After the chyme has passed through the large intestine, the digestive process is complete.

Fifth stop: the rectum

The rectum is the last piece of the colon, about eight inches long. It divides into a rectum and an anal canal, which measures approximately 3–4 centimeters. The stool can remain in the rectum for up to five days before it is finally excreted via the anal canal.

The anus, also called anus, forms a gas-tight seal. The primary muscles around the anus are unconsciously kept closed by the brain. Another muscle type ensures that bowel movements can be consciously regulated. In addition, cushion-like balls of veins seal the anus.

The feces consist of indigestible food residues, mucus, water and bacteria. The brown color comes from Sterkobilin, a breakdown product of the bile pigments.

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Mag. Julia Wild
Medical review:
Dr. Ludwig Kaspar
Editorial editing:
Nicole Kolisch

Status of medical information:
  • Elmadfa I./ Leitzmann C .: Human nutrition. 5th edition, Verlag Eugen Ulmer, Stuttgart 2015

Füeßl H .: Internal medicine in questions and answers. 8th edition, Georg Thieme Verlag, Stuttgart 2004

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