The intestine does not absorb useful substances


How does the absorption of nutrients occur?

Absorption of nutrients is the ultimate goal of the whole chain of digestion, which is carried out in the human body. It occurs in almost all parts of the digestive system and plays a very important role in the provision of normal life.

What is happening and where?

Absorption of nutrients # 8211; It is a multifaceted process that takes place in each of the digestive system.Often happens, that its functioning is broken and in order to normalize the work, it is necessary to identify the department in which the failure occurred. And this can be done only by a full understanding of all the stages of this complex physiological process.

In particular, the process is implemented:

  1. In the oral cavity. Saliva includes special enzymes that allow any carbohydrates to be broken down to the level of glucose. However, the period of food in the mouth is quite short-lived # 8211; maximum 20 seconds. During this time monosaccharides only begin the process of absorption, which will end when the food gets into the stomach. However, even there the saliva, which has been saturated with food in the mouth, will actively participate in the process.
  2. In the walls of the stomach. As a rule, it is in this department of the esophagus that the maximum percentage of water, already split in mineral salts and amino acids, is absorbed. Partially absorbed glucose, as well as alcohol. This explains the regularity of the fact that people who drink on an empty stomach get drunk very quickly.
  3. In the area of ​​the intestine (thin). The overwhelming amount of nutrients from the fissionable products is absorbed precisely in the area of ​​the small intestine. This can be explained by its specific structure, ideally adapted to perform this function. The internal cavity of the small intestine is strewn with villi, which significantly increase its area and only increase its absorbing capacity. The maximum number of amino acids, monosaccharides and nutrients complete their disintegration and are absorbed into the blood precisely here.
  4. On the surface of the large intestine. This stage is final and allows to complete the assimilation of water, salt, numerous vitamins and even monomers unaffected in the previous stages. After the final assimilation in the walls of the large intestine, the food is considered fully worked and ready for removal from the body.

The process of splitting food, on average, takes up to several hours and depends on the composition of those products that enter the body. Healthy and healthy food is split as quickly as possible, while the processing of harmful and heavy products requires much more time.

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How exactly is the absorption carried out?

With external simplicity, the suction process occurs in strict accordance with various mechanisms through which its regulation is carried out.

In particular, the salt and complex of organic components enter the body, following the laws of diffusion. Along with this, a number of other minerals enter there exclusively according to the laws of filtration provoked by contractions of the muscular area of ​​the intestine.

In addition, digestion in the intestines requires a significant expenditure of energy resources, so after eating It is strongly recommended to minimize physical activity and at least an hour just to sit or lie down. During this time, glucose, any amino acids, a vital sodium and even such a substance as fatty acids will be assimilated.

In the process of studying the question of assimilation of food in the field of the small intestine, scientists conducted Special experiments, during which by introducing certain poisons into the body, processes absorption. As a result of this experiment, the functioning of the intestine did not stop. However, the process of assimilating glucose and its accompanying sodium ions completely ceased.

Moreover, the absorption of nutrients from foods requires a significant increase in the intensity of cellular respiration and a more active reduction in villi.

In fact, the villi are a kind of pump, which promotes the movement of food leftovers on the walls of the intestine. Suction takes place through them.

It is noteworthy that during only one day about 10 liters of liquid are absorbed, about 8 liters of which are gastric juices. The main mechanism for such manipulations # 8211; it is the intestine.

People who have problems with the functioning of this element of the esophagus should seek help as soon as possible! After all, in this case, not only the condition worsens and discomfort is observed, but a deficit is formed for certain components that are no longer absorbed by this body.

And already, certainly, having passed or having taken place the recommended treatment, it will be necessary to watch own food, completely eliminating from it harmful products and substances that cause irritation and even inflammation of the walls intestines. Independently to allocate such list it is difficult enough, and it is better on this question to consult with the doctor.

Absorption of water in the small intestine. Physiology of ion absorption in the intestine

From the small intestineevery day several hundred grams of carbohydrates, 100 g or more fat, 50-100 g of amino acids, 50-100 g of ions and 7-8 l of water are absorbed. The absorption capacity of the small intestine is normally much higher, up to several kilograms per day: 500 g of fat, 500-700 g of protein and 20 l or more of water. The large intestine can absorb additional water and ions, even some nutrients.


Isotonic absorption. Water passes through the intestinal membrane completely through diffusion, which obeys the usual laws of osmosis. Consequently, when the chyme is sufficiently diluted, water is absorbed by the villi of the intestinal mucosa into the blood almost exclusively by osmosis.

Conversely, water can be transported in the opposite direction from the plasma inchyme. In particular, this occurs when a hypertonic solution from the stomach enters the duodenum. To make the chyme isotonic plasma, the required amount of water with the help of osmosis within a few minutes will be moved to the lumen of the intestine.

Physiology of ion absorption in the intestine

Active sodium transport. In the intestinal secretion, 20-30 g of sodium are released daily. In addition, daily, on average, a person eats 5-8 g of sodium. Thus, to prevent direct loss of sodium with feces, 25-35 grams of sodium should be absorbed per day in the intestine, which is approximately 1/7 of the total sodium in the body.

In situations where a significantamount of intestinal secretionis exposed outside, for example, with an extreme degree of diarrhea, sodium stores in the body can be depleted, reaching a deadly level for several hours. Usually, with feces, less than% of intestinal sodium is lost daily; it is quickly absorbed by the intestinal mucosa. Sodium also plays an important role in the absorption of sugars and amino acids, which we will see in further discussions.

The main mechanismSuction of sodium from the intestineis shown in the figure. The principles of this mechanism are basically similar to the absorption of sodium from the gallbladder and renal tubules.

Drivingforce for suction of sodiumis provided by the active excretion of sodium from the inside of the epithelial cells through the basal and lateral walls of these cells into the intercellular space. In the figure it is indicated by wide red arrows. This active transport is subject to the usual laws of active transport: it needs energy, and energy processes are catalyzed in the cell membrane by adenosine triphosphatase-dependent enzymes. Part of the sodium is absorbed together with the chlorine ions; in addition, negatively charged chlorine ions are passively attracted by positively charged sodium ions.

Active sodium transportthrough the basolateral membrane of cells reduces the concentration of sodium within the cell to low values ​​(about 50 meq / l), which is also shown in the figure. Due to the fact that the concentration of sodium in the chyme is normally around 142 mEq / L (ie, approximately equal to the content in the plasma), sodium moves inward along this steep electrochemical gradient from the chyme through the brush border into the cytoplasm of epithelial cells, which provides the main transport of sodium ions by epithelial cells into the intercellular space.

Osmosis water. The next step in transport processes is osmosis of water into the intercellular space. It occurs because a high osmotic gradient is created because of the increased concentration of ions in the intercellular space. Most of the osmosis is carried out through dense contacts of the apical border of the epithelial cells, and also through the cells themselves. Osmotic movement of water creates a flow of fluid through the intercellular space. As a result, water appears in the circulating blood of the villi.

Intestines. The human digestive system

From the stomach the food passes into the duodenum, which is the initial section of the small intestine (its total length is about 7 m).

Duodenum(cm. Fig. P. 10) in combination with the pancreas and liver is the central node of the secretory, motor and evacuation activity of the digestive system. In the stomach, the cell walls collapse (i.e. e. begins partial splitting of connective tissue proteins), in the cavity of the duodenum, the main processes of digestion of proteins, fats and carbohydrates continue. It absorbs almost all the products obtained as a result of the breakdown of nutrients, as well as vitamins, most of the water and salts.

In the small intestine(cm. Fig. P. 11) there is a final splitting of nutrients. Food gruel is processed under the influence of pancreatic juice and bile, impregnating it in duodenum, as well as under the influence of numerous enzymes produced by glands of fine guts.

The absorption process takes place on a very large surface, since the mucosa of the small intestine forms many folds. Mucous is densely strewn with villi - a kind of fingerlike protrusions (the number of villi is very large: in an adult it reaches 4 million). In addition, on the epithelial cells of the mucosa there are microvilli. All this increases the suction surface of the small intestine hundreds of times.

From the small intestine nutrients pass into the blood of the portal vein and enter the liver, where they are processed and rendered harmless, after that part of them carries with a current of blood throughout the body, penetrates through the walls of the capillaries into the intercellular spaces and further into cells. The other part (for example, glycogen) is deposited in the liver.

Diagram of the digestive system:1 - salivary glands; 2 - trachea; 3 - esophagus; 4 - diaphragm; 6 - liver; 6 - gall bladder; 7 - bile duct; 8 - stomach; 9 - pancreas gland; 10 - duodenum; 11 - small intestine; 12 - large intestine; 13 - the caecum; 14 - appendix (appendix); 15 is the straight line intestine.
In the large intestine(cm. Fig. P. 12) suction of water is completed and fecal matter is formed. Juice of the colon is characterized by the presence of mucus, in its dense part contains certain enzymes (alkaline phosphatase, lipase, amylase, etc.).

Colonis the place of abundant reproduction of microorganisms. In 1 g of feces contains several billion microbial cells. Intestinal microflora is involved in the final decomposition of the components of digestive juices and the remnants of undigested food, synthesizes enzymes, vitamins (group B and vitamin K), as well as other physiologically active substances that are absorbed into the large intestine. In addition, the intestinal microflora creates an immunological barrier against pathogenic microbes. Thus, animals grown in sterile conditions without microbes in the intestine are much more susceptible to infection than animals grown under normal conditions. Thus, it was shown that the intestinal microflora contributes to the development of natural immunity.

The microbes present in the healthy intestine perform another protective function: they have a pronounced antagonism to relation to "foreign" bacteria, including pathogens, and thereby protect the host organism from their introduction and reproduction.

The protective functions of normal intestinal microflora suffer particularly sharply when antibacterial drugs are introduced into the gastrointestinal tract. In experiments on dogs suppression of normal microflora with antibiotics caused abundant growth in the large intestine of yeast-like fungi. Clinical observations have shown that too prolonged use of antibiotics often causes severe complications caused by stormy the multiplication of antibiotic-resistant forms of staphylococci and E. coli, not restrained by the more competing microorganisms.

Intestinal microfloradecomposes the excess enzymes of the pancreatic juice (trypsin and amylase) and bile, promotes the breakdown of cholesterol.

In humans, about 4 kg of food masses per day pass from the small intestine to the thick intestine. In the cecum (see Fig. Fig. 13) food gruel continues to be digested. Here, with the help of enzymes produced by microbes, fiber is broken down and water is sucked in, then the food masses gradually turn into feces. This is facilitated by movements of the large intestine that mix the food pulp and promote the absorption of water. A day produces an average of 150-250 g of generated stool, about one third of them are bacteria.

The nature of the stool and its amount depend on the composition of the food.When feeding mainly plant food stool mass is much more than when feeding mixed or meat food. After eating rye bread or potatoes, 5-6 times more feces are formed than after the same amount of meat.

The act of defecation has a reflex effect on the cardiovascular system. At this time, the maximum and minimum arterial blood pressure rises, the heart rate increases by 15-20 beats per minute. Most healthy people have a stool once a day.

The liberation of the intestine from fecal matter is provided by active peristalsis, which occurs when the intestinal wall receptors are irritated by the colonic masses. When eating foods that contain a sufficient amount of vegetable fiber, its coarse undigested fibers irritate nerve endings in the muscles of the thin, and especially the large intestine, and thus cause peristaltic movements that accelerate the movement of the food gruel. Lack of fiber complicates the release of the intestine, since a weak peristalsis, much less its absence, causes a prolonged delay in guts of food remnants, which can cause various diseases of the digestive system (eg, dysfunction of the gallbladder, hemorrhoids). With chronic constipation, the feces strongly dehydrate, as in the colon there is an excessive absorption of water, which under normal conditions is to be removed with feces. In addition, too long a stool in the large intestine (ie, e. chronic constipation) breaks the intestinal "barrier and the walls of the intestine begin to flow into the blood not only water with small molecules nutrients, but also harmful to the body large molecules of products of decay and fermentation - self-poisoning takes place organism.



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