Digestion of lipids in the gastrointestinal tract. Biochemistry nutrition and digestion

Thank you

The site provides reference information solely to familiarize yourself. Diagnosis and treatment of diseases must be under the supervision of a specialist. All drugs have contraindications. Consultation of a specialist is obligatory!

What kind of lipid substances?

Lipids represent one of the groups of organic compounds having a great importance for living organisms. In the chemical structure, all lipids are divided into simple and complex. The molecule of simple lipids consists of alcohol and bile acids, while the composition of complex lipids includes other atoms or connections.

In general, lipids are of great importance for humans. These substances are included in a significant portion of food, used in medicine and pharmacy, play an important role in many industries. In the living organism of lipids in one form or another part of all cells. From the point of view of nutrition is a very important source of energy.

What is the difference between lipids and fats?

In principle, the term "lipids" comes from the Greek root, meaning "fat", but these definitions still have some differences. Lipids are a more extensive group of substances, while only some types of lipids are understood under fats. The synonym for "fats" are "triglycerides", which are obtained from the compound of alcohol glycerol and carboxylic acids. Both lipids in general and triglycerides in particular play a significant role in biological processes.

Lipids in the human body

Lipids are part of almost all body tissues. There are molecules in any live cage, and without these substances, life is simply impossible. There are a lot of different lipids in the human body. Each type or class of these connections has its own functions. Many biological processes depends on the normal receipt and formation of lipids.

From the point of view of biochemistry, lipids take part in the following most important processes:

• production of energy;

• cell division;
• transmission of nerve impulses;
• the formation of blood components, hormones and other important substances;
• protection and fixation of some internal organs;
• cellular division, breathing, etc.

Thus, lipids are vital chemical compounds. A significant part of these substances enters the body with food. After that, the structural components of lipids are absorbed by the body, and the cells produce new lipid molecules.

Biological role of lipids in a living cell

Lipid molecules perform a huge number of functions not only on the scale of the entire body, but also in each living cell separately. In fact, the cell is a structural unit of a living organism. It takes assimilation and synthesis ( education) certain substances. Some of these substances goes to maintain the vital activity of the cell itself, part of the division of the cell, part - on the needs of other cells and tissues.

In the living organism of lipids, the following functions perform:

• energy;
• reserve;
• structural;
• transport;
• enzymatic;
• stocking;
• signal;
• regulatory.

Energy function

The energy function of lipids is reduced to their decay in the body, in the process of which a large amount of energy is distinguished. Alive cells this energy is necessary to maintain various processes ( breathing, growth, division, synthesis of new substances). Lipids enter the cage with the influx of blood and postponed inside ( in cytoplasm) In the form of small drops of fat. If necessary, these molecules are split, and the cell receives energy.

Backup ( flashing) Function

The backup function is closely related to the energy. In the form of fats inside cells, the energy can be postponed "about the supply" and stand out as needed. Special cells are responsible for the accumulation of fats - adipocytes. Most of Their volume is occupied by a large drop of fat. It is from adipocytes that the body fabric consists in the body. The greatest reserves of adipose tissue are in subcutaneous fatty tissue, a large and small seal ( in abdominal cavity ). With long starvation, adipose tissue is gradually decaying, as lipid reserves are used to produce energy.

Also, fatty fabric, peculiar in subcutaneous fluid, carries out thermal insulation. Fabrics rich in lipids are generally worse than spending warmth. This allows the body to support permanent temperature Bodies and not so quickly cooled or overheat in various conditions of the external environment.

Structural and barrier functions ( membrane lipids)

Lipids are played a huge role in the structure of living cells. In the human body, these substances form a special double layer, which forms the cell wall. Due to this, the live cell can perform its functions and adjust the metabolism with the external environment. Lipids forming the cell membrane also allow you to preserve the shape of the cell.

Why lipids monomers form a double layer ( bisoy)?

Monomers are called chemical substances (in this case, molecules) who are capable of connecting, forming more complex compounds. Cell wall consists of a double layer ( bISOTEY.) Lipid. Each molecule forming this wall has two parts - hydrophobic ( not in contact with water) and hydrophilic ( contact with water). The double layer is obtained due to the fact that lipid molecules are deployed by hydrophilic parts inside the cell and the dust. The hydrophobic parts are practically contacting, since they are between two layers. In the thicker of lipid bilaying, other molecules can be located ( proteins, carbohydrates, complex molecular structures), which regulate the passage of substances through the cell wall.

Transport function

Lipid transport function has a secondary value in the body. It is performed only by some connections. For example, lipoproteins consisting of lipids and proteins carry some substances from one body to another. However, this function is rarely isolated, not counting its main for these substances.

Enzymatic function

In principle, lipids are not part of the enzymes involved in the splitting of other substances. However, without lipids, the organs of organs will not be able to synthesize enzymes, the final product of vital activity. In addition, some lipids play a significant role in assimilating fats coming from food. The bile contains a significant amount of phospholipids and cholesterol. They neutralize the excess of the pancreas enzymes and do not give them damage the intestinal cells. Also in bile there is a dissolution ( emulsification) Exogenous lipids coming with food. Thus, lipids play a huge role in digestion and help in the work of other enzymes, although the enzymes themselves are not.

Signal function

Some of the complex lipids performs a signal function in the body. It is to maintain various processes. For example, glycolipids in nerve cells take part in the transmission of the nerve impulse from one nervous cell to another. In addition, signals inside the cell itself are of great importance. She needs to "recognize" the substances that come with the blood to transport them inside.

Regulatory function

The regulatory function of lipids in the body is secondary. The lipids themselves are little affected by the course of various processes. However, they are part of other substances that are of great importance in the regulation of these processes. First of all, these are steroid hormones ( hormones of adrenal and sex hormones). They play an important role in the exchange of substances, the growth and development of the body, reproductive functionaffect the work immune system. Also lipids are included in the composition of prostaglandins. These substances are produced under inflammatory processes and affect some processes in nervous system (for example, pain perception).

Thus, the lipids themselves do not perform the regulatory function, but their drawback can affect many processes in the body.

Biochemistry of lipids and their connection with other substances ( squirrels, Carbohydrates, ATP, Nucleic Acids, Amino Acid, Steroids)

Lipid exchange is closely related to the exchange of other substances in the body. First of all, this connection is traced in human nutrition. Any food consists of proteins, carbohydrates and lipids, which should fall into the body in certain proportions. In this case, a person will receive and enough energy, and enough structural elements. Otherwise ( for example, with a lack of lipids) Proteins and carbohydrates will be cleaving for energy production.

Also lipids to one degree or another are associated with the exchange of the following substances:

• Adenosine trifosphoric acid ( ATF). ATP is a peculiar unit of energy inside the cell. When lipids splitting, part of the energy goes to the production of ATP molecules, and these molecules take part in all intracellular processes ( transportation of substances, cell division, neutralization of toxins, etc.).
• Nucleic acids. Nucleic acids are structural elements of DNA and are in the nuclei of living cells. The energy generated by fats when splitting fats is partly for cell division. During division, the formation of new DNA chains from nucleic acids occurs.
• Amino acids. Amino acids are the structural components of proteins. In conjunction with lipids, they form complex complexes, lipoproteins responsible for the transport of substances in the body.
• Steroids. Steroids are the form of hormones containing a significant amount of lipids. With a bad assimiment of lipids from food, patient may begin problems with the endocrine system.

Thus, the exchange of lipids in the body in any case should be considered in the complex, in terms of interconnection with other substances.

Digestion and suction of lipids ( metabolism metabolism)

Digestion and suction of lipids is the first stage of the exchange of these substances. The main part of lipids enters the body with food. IN oral cavity Food grinding and mixing it with saliva. Next, the lump falls in the stomach, where chemical bonds are partially destroyed under the action of hydrochloric acid. Also, some chemical bonds in lipids are destroyed by the enzyme of the lipase contained in saliva.

Lipids are insoluble in water, so in duodenalistician They are not immediately exposed to enzymes. First, the so-called emulsification of fats occurs. After that, chemical ties are split under the action of lipase coming from the pancreas. In principle, for each type of lipids, its enzyme is now defined, which is responsible for the splitting and absorption of this substance. For example, phospholipase cleaves phospholipids, cholesterol easerase - cholesterol compounds, etc. All these enzymes in one or another quantity are contained in the pancreas juice.

Split fragments of lipids are absorbed separately by cells fine intestine. In general, the digestion of fats is quite difficult processwhich is regulated by a plurality of hormones and hormone-like substances.

What is lipid emulsification?

Emulsification is an incomplete dissolution of fatty substances in water. In the food lump falling into a duodenum, fats are contained in the form of large droplets. This prevents their interaction with enzymes. In the process of emulsifying, large fat drops are "crushed" on the smaller droplets. As a result, the area of \u200b\u200bcontact of fat droplets and surrounding water soluble substances increases, and it becomes possible to split lipids.

The emulsification process of lipids in digestive system Passes in several stages:

• At the first stage, the liver produces bile, which will emulsify fats. It contains salts cholesterol and phospholipids that interact with lipids and contribute to their "crushing" into small drops.
• The bile, isolated from the liver, accumulates in the bustling bubble. Here it concentrates and stands out as needed.
• When consuming fatty foods, to smooth muscles Gallbladder comes to reduce. As a result, the bile portion of biliary ducts is highlighted in the duodenum.
• In the duodenum intestine, there is actually emulsification of fats and their interaction with pancreatic enzymes. Reducing the walls of the small intestine contribute to this process, "stirring" content.

In some people, after removing the gallbladder, problems may arise with the absorption of fats. Bile enters the duodenum continuously, directly from the liver, and it lacks it for emulsifying the entire volume of lipids if too much is eaten.

Lipid splitting enzymes

To digest each substance in the body there are their enzymes. Their task is to destroy the chemical bonds between molecules ( or between atoms in molecules) So that the useful substances can normally be absorbed by the body. Different enzymes are responsible for splitting different lipids. Most of them are contained in the juice allocated to the pancreas.

The following groups of enzymes are responsible for splitting lipids:

• lipases;
• phospholipase;
• cholesterolhesterase, etc.

What vitamins and hormones are involved in the regulation of lipid levels?

The level of most lipids in human blood is relatively constant. It can fluctuate under certain limits. It depends on the biological processes occurring in the body itself, and from a number of external factors. Regulation of the level of lipids in the blood is a complex biological process in which many different organs and substances take part.

The greatest role in assimilating and maintaining the permanent level of lipids is played by the following substances:

• Enzymes. A number of pancreatic enzymes take part in the splitting of lipids entering the body with food. With the lack of these enzymes, the level of lipids in the blood may decrease, since these substances simply will not be used in the intestine.
• Bile acids and their salts. The bile contains bile acids and a number of their compounds that contribute to the emulsification of lipids. Without these substances, the normal absorption of lipids is also impossible.
• Vitamins. Vitamins have a comprehensive strengthening effect on the body and directly or indirectly affect lipids. For example, with a lack of vitamin A, the regeneration of cells in mucous membranes deteriorates, and the digestion of substances in the intestine is also slowed down.
• Intracellular enzymes. In the cell epithelial cells contain enzymes, which, after suction of fatty acids, convert them into transport shapes and sent to the bloodstream.
• Hormones. A number of hormones affect the exchange of substances in general. For example, high level Insulin can greatly affect the level of lipids in the blood. That is why for patients with diabetes mellitus, some norms are revised. Thyroid hormones, glucocorticoid hormones or norepinephrine can stimulate the decay of adipose tissue with energy release.

Thus, maintaining a normal level of lipids in the blood is a very complex process, which is directly or indirectly affected by different hormones, vitamins and other substances. In the process of diagnostics, the doctor must be determined at what stage this process was broken.

Biosynthesis ( education) and hydrolysis ( decay) Lipids in the body ( anabolism and catabolism)

Metabolism is called aggregate exchange processes in organism. All metabolic processes can be divided into catabolic and anabolic. Catabolic processes include splitting and decomposition of substances. In relation to lipids, this is characterized by their hydrolysis ( disintegration) In the gastrointestinal tract. Anabolism unites biochemical reactions aimed at the formation of new, more complex substances.

Lipid biosynthesis occurs in the following fabrics and cells:

• Cells of the intestine epithelial. In the intestinal wall there is absorption of fatty acids, cholesterol and other lipids. Immediately after that, new, transport forms of lipids are formed in the same cells, which fall into venous blood and are sent to the liver.
• Liver cells. In the liver cells, some of the lipid transport forms will break up, and new substances are synthesized from them. For example, there is a formation of cholesterol and phospholipids compounds, which are then highlighted with bile and promote normal digestion.
• Cells of other organs. Part of lipids falls with blood to other organs and fabrics. Depending on the type of cells, lipids are converted into a certain type of compounds. All cells, one way or another, synthesize lipids for the formation of a cell wall ( lipid bisloga). In adrenal glands and sex glasses, steroid hormones are synthesized from the part of lipids.

The combination of the processes described above and is the metabolism of lipids in the human body.

Resintez lipids in the liver and other organs

The reintestas is called the formation process of certain substances from the simpler, which was learned before. In the body, this process proceeds in the inner medium of some cells. Resintez is necessary in order for the fabrics and organs to receive all the necessary types of lipids, and not just those that were used with food. Resintezed lipids are called endogenous. The organism exists in their formation.

At the first stage, the residence of lipids occurs in the intestinal walls. Here, the fatty acids come from food are converted into transport forms that will go with blood to the liver and other organs. Part of the resintezed lipids will be delivered to the tissue, from the other part are formed by the substances necessary for life ( lipoproteins, bile, hormones, etc.) The excess is converted into fatty tissue and postponed "stock".

Do lipids enter the composition of the brain?

Lipids are a very important component of the nerve cells not only in the brain, but also in the entire nervous system. As is known, nerve cells control various processes in the body by transferring the nerve impulses. At the same time, all the nerve paths are "isolated" from each other, so that the impulse comes to certain cells and did not affect other nervous paths. Such "insulation" is possible due to myelin shell of nerve cells. Myelin that prevents the chaotic spread of impulses, about 75% consists of lipids. As in the cell membranes, here they form a double layer ( bisoy), which is wrapped several times around the nervous cell.

The composition of the myelin shell in the nervous system includes the following lipids:

• phospholipids;
• cholesterol;
• galactolipids;
• glycolipids.

In some congenital violations of the formation of lipids, neurological problems are possible. This is due precisely by thinning or interruption of myelin shell.

Lipid hormones

Lipids play an important structural role, including those present in the structure of many hormones. Hormones, which include fatty acids, are called steroid. In the body they are produced by sex and adrenal glands. Some of them are present in the cells of adipose tissue. Steroid hormones take part in the regulation of many vital important processes. Their imbalance may affect the body weight, the ability to conceive a child, the development of any inflammatory processes, work of the immune system. The key to normal production of steroid hormones is balanced lipid consumption.

Lipids are part of the following vital hormones:

• corticosteroids ( cortisol, aldosterone, hydrocortisone, etc.);
• men's sex hormones - Androgens ( androtandion, Dihydrotestosterone, etc.);
• women's sex hormones - estrogens ( estriol, estradiol, etc.).

Thus, the lack of some fatty acids in food can seriously affect the work of the endocrine system.

Lipid role for leather and hair

Lipids for the health of the skin and its appendages are of great importance ( hair and nails). The skin contains the so-called sebaceous glandswhich allocate a certain amount rich in fats on the surface. This substance performs many useful features.

For hair and skin lipids are important for the following reasons:

• a significant part of the hair substance consists of complex lipids;
• skin cells change rapidly, and lipids are important as an energy resource;
• secret ( selected substance) song hardware moisturizes the skin;
• thanks to the fats, the elasticity, elasticity and smoothness of the skin are maintained;
• a small amount of lipids on the surface of the hair gives them a healthy shine;
• the lipid layer on the surface of the skin protects it from the aggressive impact of external factors ( cold, sun rays, microbes on the surface of the skin, etc.).

In the skin cells, like in the hair onion, lipids come with blood. Thus, normal nutrition provides skin and hair health. The use of shampoos and creams containing lipids ( especially indispensable fatty acids) It is also important because some of these substances will be absorbed from the cell surface.

Lipid classification

In biology and chemistry there are quite a lot different classifications lipids. The main is chemical classificationAccording to which lipids are divided depending on their structure. From this point of view, all lipids can be divided into simple ( consisting only of oxygen, hydrogen and carbon atoms) and complex ( including at least one atom of other elements). Each of these groups has appropriate subgroups. This classification is most convenient, as it reflects not only the chemical structure of substances, but also partially determines the chemical properties.

In biology and medicine, there are additional classifications that use other criteria.

Exogenous and endogenous lipids

All lipids in the human body can be divided into two large groups - Exogenous and endogenous. The first group includes all substances falling into the body from the external environment. The greatest amount of exogenous lipids enters the body with food, however, there are other ways. For example, when applying various cosmetics or medicinal preparations The body can also receive a certain amount of lipids. Their action will be mainly local.

After entering the body, all exogenous lipids are split and digested by alive cells. Here, other lipid compounds will be formed from their structural components in which the body needs. These lipids synthesized with their own cells are called endogenous. They may have a completely different structure and functions, but consist of the same "structural components", which fell into the body with exogenous lipids. That is why, with a lack of food in food, certain types of fat may develop various diseases. A part of the components of complex lipids cannot be synthesized by the body independently, which is reflected in the course of certain biological processes.

Fatty acid

Fatty acids are called the class of organic compounds that are structural part of lipids. Depending on which fatty acids are part of the lipid, the properties of this substance may vary. For example, triglycerides, the most important source of energy for the human body, are derivatives of glycerin alcohol and several fatty acids.

In nature, fatty acids are contained in various substances - from oil to vegetable oils. In the human body, they fall mainly with food. Each acid is a structural component for certain cells, enzymes or connections. After suction, the body converts it and uses in various biological processes.

The most important sources of fatty acids for humans are:

• animal fats;
• vegetable fats;
• tropical oils ( citrus, palm, etc.);
• fats for the food industry ( margarine et al.).

In the human body, fatty acids can be delayed in adipose tissue as part of triglycerides or circulated in blood. In the blood, they are contained both in free form and in the form of connections ( various fractions of lipoproteins).

Saturated and unsaturated fatty acids

All fatty acids in their chemical structure are divided into saturated and unsaturated. Saturated acids are less useful for the body, and some of them are even harmful. This is due to the fact that there are no double ties in the molecule of these substances. These are chemically stable compounds, and they are worse assimilated by the body. Currently, the connection of some saturated fatty acids with the development of atherosclerosis has been proved.

Unsaturated fatty acids are divided into two large groups:

• Mononanaturated. These acids have one double bond in their structure and are thus more active. It is believed that their eating can reduce cholesterol levels and prevent the development of atherosclerosis. The largest number of monon-saturated fatty acids is contained in a number of plants ( avocado, olives, pistachios, forest nuts) And, accordingly, in the oils obtained from these plants.
• Polyunsaturated. Polyunsaturated fatty acids have several double bonds in their structure. A distinctive feature these substances are that human body It is not capable of synthesize them. In other words, if the body does not flow with food polyunsaturated fatty acids, over time it will inevitably lead to certain violations. The best sources of these acids are seafood, soy and flaxseed oil, sesame seeds, poppy, germinated wheat, etc.

Phospholipids

Phospholipids are complex lipids containing in their composition the residue of phosphoric acid. These substances, along with cholesterol, are the main component of cell membranes. Also these substances take part in the transport of other lipids in the body. FROM medical point Phospholipids can also perform a signal role. For example, they are part of bile, as they contribute to emulsification ( dissolution) Other fats. Depending on what substance in bile more, cholesterol or phospholipids, it is possible to determine the risk of developing biliary diseases.

Glycerin and triglycerides

According to the chemical structure, the glycerin is not lipid, however, it is an important structural component of triglycerides. This is a group of lipids playing a huge role in the human body. The most important feature of these substances is the supply of energy. Triglycerides entering the body with food are split into glycerin and fatty acids. As a result, a very large amount of energy is distinguished, which goes to the work of the muscles ( skeletal muscles, heart muscles, etc.).

Fat fabric in the human body is represented mainly triglycerides. Most of these substances, before postponing in adipose tissue, undergoes some chemical transformation in the liver.

Beta lipids

Beta lipids are sometimes called beta lipoproteins. The duality of the name is explained by differences in classifications. This is one of the fractions of lipoproteins in the body, which plays an important role in the development of some pathologies. First of all, we are talking about atherosclerosis. Beta lipoproteins are transported by cholesterol from some cells to others, but due to the characteristics of the structure of molecules, this cholesterol is often "stuck" in the vessel walls, forming atherosclerotic plaques and preventing normal blood flow. Before use, you must consult with a specialist.

In the cavity of the mouth of the lipids are only machined. The stomach has a small amount of lipase, which hydrolyzes fats. The small activity of the gastric juice lipase is associated with the acidic reaction of the contents of the stomach. In addition, lipase can only affect emulsified fats, there are no conditions in the stomach for the formation of fat emulsion. Only in children and monotrustic animals of lipase gastric juice plays an important role in digesting lipids.

The intestine is the main place of digestion of lipids. In the twelfth gauge, the bile liver and the pancreas juice affects the lipids, at the same time there is neutralization of intestinal contents (chimus). There is an emulsification of fats under the action of bile acids. The bile includes: chill acid, deoxychole (3.12 dihydroxycholane), minoroxychole (3.7 dihydroxycholane) acid, sodium salts of paired bile acids: glycochole, glycodeoxychole, Taurochole, Taurodezoxychole. They consist of two components: chill and deoxycolic acids, as well as glycine and taurine.

deoxycholic acid Henodoxicole acid

glycochole acid

taurocholic acid

Salts of bile acids well emulsified fats. At the same time, the area of \u200b\u200bcontact with fats enzymes increases and the enzyme action increases. Insufficiency of the synthesis of bile acids or delay of admission violates the effectiveness of enzymes. Fats, as a rule, are absorbed after hydrolysis, but some of the finely emulsified fats are absorbed through the intestinal wall and proceeds to lymph without hydrolysis.

Esterase breaks into fats the essential bond between, alcohol group and carboxyl group of carboxylic acids and inorganic acids (lipase, phosphatases).

Under the action of lipase, fats are hydrolyzed on glycerin and higher fatty acids. The activity of lipase increases under the action of bile, i.e. Bile directly activates lipase. In addition, the activity of the lipase increases CA ++ ions due to the fact that Ca ++ ions form insoluble salts (soaps) with exemplary fatty acids and prevent their overwhelming effect on the activity of the lipase.

Under the action of lipase, essential bonds at α and α 1 (side) carbon atoms of glycerol are hydrolyzed, then in the β-carbon atom:

Under the action of lipase, up to 40% of triacyl glycerides are cleaved to glycerol and fatty acids, 50-55% hydrolyzed to 2 monoacyl glycerolins and 3-10% is not hydrolyzed and absorbed in the form of triacylglycerin.

The sherids of the feed are split by the enzyme cholesterol elase to cholesterol and higher fatty acids. Phosphatides are hydrolyzed under the influence of phospholipase A, A 2, C and D. Each enzyme is valid for a certain ester bond of lipid. Points of application phospholipas are represented in the diagram:

Pancreas phospholipases, tissue phospholipases are produced in the form of pro-ferrises and activated by trypsin. Phospholipase A 2. snake poison Catalyzes the cleavage of unsaturated fatty acid in position 2 of phosphoglycerides. At the same time, lizolecitins are formed with a hemolytic action.

phosphothidilcholine Lizolecin

Therefore, when this poison appears in blood, severe hemolysis occurs .. In the intestine, this danger is eliminated by the effect of phospholipase A 1, quickly inactivating lysophosphatid as a result of the remnant of saturated fatty acid from it with the transformation of it into inactive glyceluphospholine.

Lysolecitins in low concentrations stimulate differentiation of lymphoid cells, the activity of protein kinase C, reinforce cell proliferation.

ColoMindhosphatides and serinal phosphatides are cleaved by phospholipase A to lesocolminofosphatides, lysoserinphosphatides, which are further split by phospholipasis A 2 . Phospholipase C and D hydrolyzing the links of choline; Collamin and serine with phosphoric acid and phosphoric acid residue with glycerin.

The absorption of lipids occurs in the subtle intestinal department. Fatty acids with a chain length of less than 10 carbon atoms are absorbed in a non-esterified form. For suction it is necessary to the presence of emulsifying substances - bile acids and bile.

Resintez fat characteristic of this organism, occurs in the intestinal wall. The concentration of blood lipids for 3-5 hours after feeding the feed is high. Hilomikrons - Small fat particles formed after suction in the intestinal wall are lipoproteins surrounded by phospholipids and a protein shell, inside contain fat and bile acid molecules. They enter the liver, where lipids are subjected to intermediate exchange, and bile acids pass in gall-bubble And then back to the intestines (see Fig. 9.3 on page 192). As a result of such a circuit, a small amount of bile acids is lost. It is believed that the molecule of bile acid per day performs 4 circles.

Digestion of lipids in the intestine.

19.1.1. The main place of digestion of lipids is top department small intestine. For digesting lipids, the following conditions are necessary:

the presence of lipolytic enzymes;

conditions for lipid emulsification;

the optimal pH values \u200b\u200bof the medium (in the range of 5.5 - 7.5).

19.1.2. Various enzymes participate in lipid splitting. Food fats in an adult are split in mainly pancreatic lipase; Lipase in intestinal juice is also found, in saliva, in breast children are active in the stomach. Lipases refer to the hydrolyz class, they hydrolyze the ester bonds -O-method formation of free fatty acids, diacyl glycerols, monoacyl glycers, glycerol (Figure 19.1).

Figure 19.1. Scheme of hydrolysis of fats.

The glyceluphospolipids incoming with food are exposed to specific hydrolauses - phospholipas, splitting the ester bonds between phospholipid components. The specificity of the effect of phospholipas is shown in Figure 19.2.

Figure 19.2. The specificity of the action of enzyme splitting phospholipids.

Products of phospholipid hydrolysis are fatty acids, glycerol, inorganic phosphate, nitrogenous bases (choline, ethanolamine, serine).

Cholesterol food esters are hydrolyzed by pancreatic cholesterol elase with cholesterol and fatty acids.

19.1.3. Understand the features of the structure of bile acids and their role in digesting fats. Bile acids - the final product of cholesterol sharing, are formed in the liver. These include: chill (3,7,12-trioxichane), minoroxychole (3.7-dioxicolane) and deoxychole (3, 12-dioxicolane) acids (Figure 19.3, a). The first two are primary bile acids (are formed directly in hepatocytes), deoxychole - secondary (as it is formed from primary bile acids under the influence of intestinal microflora).

In bile, these acids are present in conjugated form, i.e. In the form of compounds with glycine H 2 N -CH 2 -Con or Taurine H 2 N -CH 2 -CH 2 - SO 3 H (Figure 19.3, b).

Figure 19.3. The structure of non-conjugated (a) and conjugated (b) bile acids.

19.1.4. Gallers have amphilic properties: hydroxyl groups and side chain hydrophilic, cyclic structure of hydrophobic. These properties determine the participation of bile acids in the digestion of lipids:

1) bile acids are capable of emulsifying fats, their molecules are adsorbed on the surface of fat droplets, at the same time, hydrophilic groups are involved in interaction with the surrounding water. As a result, the surface tension on the boundary of the lipid and aqueous phase section is reduced, as a result of which large fat drops are broken into smaller;

2) bile acids along with Kolindase bile are involved in the activation of pancreatic lipase, shifting it with the optimum pH in the acidic side;

3) bile acids form water-soluble complexes with hydrophobic products, which contributes to their absorption into the wall of the small intestine.

Bile acids penetrating in the process of suction together with hydrolysis products in enterocytes, through the portal system is entered into the liver. These acids can be re-secreted with bile in the intestines and participate in digestion and suction processes. Such an entero-hepatic circulation of bile acids can be carried out up to 10 or more times a day.

19.1.5. Features of suction of hydrolysis products of fats in the intestine are presented in Figure 19.4. In the process of digestion of food triacyl glycers, about 1/3 are split completely to glycerol and free fatty acids, approximately 2/3 is hydrolyzed partially with the formation of mono and diacylglycers, the small part is not split at all. Glycerol and free fatty acids with a chain length of up to 12 carbon atoms are soluble in water and penetrate into enterocytes, and from there through a duty vein in the liver. Longer fatty acids and monoacilglycerol are absorbed with the participation of conjugated bile acids forming micelles. Unstressed fats seem to be absorbed by cells of the intestinal mucosa by pinocytosis. Cholesterol insoluble in water, like fatty acids, is absorbed in the intestine in the presence of bile acids.

Figure 19.4. Digestion and suction of acyl glycers and fatty acids.

Section 19.2.

Resintez lipids in the intestinal wall and the formation of chylomikrons.

19.2.1. In the cells of the intestinal mucosa, lipids specific to the digestion of food lipids are synthesized (the fatty acid composition of such lipids corresponds to the fatty acid composition of endogenous fats). In the process of resintez, the triacylglycerols, as well as phospholipids and cholesterol esters, are formed.

19.2.2. Transportation of resintezed lipids from the intestinal wall occurs in the form of chylomicon. Hilomikrons are complex particles consisting of lipids and proteins. They have a spherical shape, their diameter is about 1 μm. Lipid kernel of chylomicrons form triacylglycerol (80% or more) and cholesterol esters. The chilomicron shell is amphiphilic compounds - proteins (apolipoproteins), phospholipids and free cholesterol (see Figure 19.5).

Figure 19.5. The scheme of the Hilomicron structure.

Hilomikrons are the transport form of lipids from the intestine to other organs and tissues; They come from the cells of the mucosa first in lymph, and then into blood. The cells of the endothelium of blood capillaries of adipose tissue, liver cells and other organs contain an enzyme lipoproteinlipase. Lipoproteinlipase affects the chylomicon, the hydrolysis of fats included in their composition (see below 19.5.2 and Figure 19.9).

19.2.3. The free fatty acids (CZP) are generated during catabolism (SZhK) are transported in the blood in the complex with albumin proteins. The blood samples are absorbed and used by cells of adipose tissue and other organs.

The CZhK is also entered into blood as a result of lipolysis of tiacyl glycers of adipose tissue. These lipolysis reactions catalyze tissue lipase. The activity of this enzyme is regulated by hormones. For example, the hormones are adrenaline and glucagon activate lipase and enhance lipolyase processes, hormone insulin contributes to the slowdown of lipolysis in adipose tissue.

The main ways of education and the use of free fatty acids are presented in Figure 19.6.

Figure 19.6. The main ways of formation and use of fatty acids.

The first two stages of digestion of lipids, emulsification and hydrolysis, occur almost simultaneously. At the same time, hydrolysis products are not removed, while remaining the composition of lipid droplets, facilitate further emulsification and operation of enzymes.

Digestion in the oral cavity

In adults in the oral cavity, the digestion of lipids does not go, although prolonged food chewing contributes to partial emulsification of fats.

Digestion in the stomach

The own lipase of the stomach in an adult does not play a significant role in digesting lipids due to its small number and that its optimum pH is 4.5-5.5. Also affects the absence of emulsified fats in ordinary food (except for milk).

However, adults have a warm medium and a stomach peristalistic causes some emulsification Fats. At the same time, even low active lipase splits minor quantities of fat, which is important for further digestion of fats in the intestine, because The presence of at least minimal amount of free fatty acids facilitates the emulsification of fats in the duodenum and stimulates the secretion of pancreatic lipase.

Digestion in the intestines

Under influence peristaltics TGC and composite components bile Food fat is emulsified. Formed during digestion lizophospholipids Also are a good surfactant, so they contribute to the further emulsification of food fats and the formation of micelles. The size of the drops of such a fat emulsion does not exceed 0.5 microns.

HS hydrolysis is carried out cholesterol-Esterates pancreatic juice.

The digestion of the tag in the intestine is carried out under the influence pancreatic lipase with an optimum pH 8.0-9.0. In the intestine it comes in the form prolipasesFor the manifestation of its activity requires a colipase that helps lipase to settle on the surface of the lipid drop.

KolipaseIn turn, activated by trypsin and then forms a complex with a lipase in a ratio of 1: 1. Pancreatic lipase clears fatty acids associated with 1 and with 3 carbon atoms of glycerol. As a result of its work, 2-monoacilglycerol (2-magazine), which are absorbed or turning monoglycerol Isomerase in 1 magazine. The latter is hydrolyzed to glycerol and fatty acid. Approximately 3/4 tag after hydrolysis remain in the form 2-magazine and only 1/4 part of the tag is hydrolyzed completely.

Full enzymatic hydrolysis of triacylglycerol

IN pancreaticthe juice also has activated phospholipase A 2 activated by trypsin, pouring fatty acid from C 2 in phospholipids from C 2, phospholipase activity with and lysophospholipase.

The effect of phospholipase A 2 and lysophospholipase on the example of phosphatidylcholine

IN intestinalthe juice also has the activity of phospholipase A 2 and phospholipase S.

For the operation of all these hydrolytic enzymes in the intestine, ions of Ca 2+ are needed, contributing to the removal of fatty acids from the catalysis zone.

Points of action phospholipas

Mizel

As a result of the impact on emulsified fats, the enzymes of pancreatic and intestinal juices are formed 2 monoacilglycerol.s, free fatty acid and free cholesterolforming the structures of micellar type (size is already about 5 nm). Free glycerol is absorbed directly into the blood.

Page 1

In the digestive processes, all washesy lipids (fats, phospholipids, glycolipids, sherids) are subjected to hydrolysis on composite parts, already mentioned earlier, the sterols are not subjected to chemical changes. When studying this material, attention should be paid to the differences in the digestion of lipids from the respective processes for carbohydrates and proteins: a special role of bile acids in the decay of lipids and the transport of digestion products.

Food lipids prevail triglycerides. Phospholipids, streynes and other lipids are consumed significantly less.

Most of the triglycerides coming from food is split to monoglycerides and fatty acids in the small intestine. The hydrolysis of fats occurs under the influence of lipases of the pancreatic juice and the mucous membrane of the small intestine. Salts of bile acids and phospholipids penetrating from the liver into the clearance of the small intestine in the composition of bile, contribute to the formation of stable emulsions. As a result of emulsification, the area of \u200b\u200bcontact of the resulting fat droplets of fat has increased dramatically. aqueous solution Lipases, and this most increases the lipolytic effect of the enzyme. The salts of bile acids stimulate the process of splitting fat not only participating in their emulsification, but also by activating lipase.

The splitting of steroids occurs in the intestine with the participation of the enzyme of the cholinesterase released with the pancreas juice. As a result of hydrolysis of steroids, fatty acids and cholesterol are formed.

Phospholipids are split completely or partially under the action of hydrolytic enzymes - specific phospholipas. The product of full phospholipid hydrolysis is: glycerin, higher fatty acids, phosphate acid and nitrogen bases.

The absorption of fat digestion products is preceded by the formation of micelles - supramolecular formations or associates. Micelles contain as the main component of the salts of bile acids, in which fatty acids, monoglycerides, cholesterol, and the like are dissolved.

In the cells of the intestinal wall of the digestion products, and in the cells of the liver, adipose tissue and other organs from precursors arising in the exchange of carbohydrates and proteins, the molecules of specific lipids of the human body - residence of triglycerides and phospholipids are constructed. However, their fatty acid composition compared with food fats is changed: in triglycerides, the intestine synthesized in the mucous membrane contains arachidon and linolenic acid even if they are absent in food. In addition, in the cells of the intestinal epithelium, the fatty drop is covered with a protein shell and the formation of chylomikrons is a large fat drop, surrounded by a small amount of protein. Transports exogenous lipids to the liver, adipose tissue, connect fabric, myocardium. Since lipids and some of their components are insoluble in water, for transferring from one body to another, they form special transport particles, as part of which is a protein component. Depending on the place of formation, these particles differ in the structure, the ratio of components and density. If the particles are dominated in such a particle in the percentage ratio of fats over proteins, then such particles are called very low density lipoproteins (LPONP) or low density lipoproteins (LDL). As increasing percentage content Protein (up to 40%) The particle turns into high density lipoproteins (HDL). Currently, the study of such transport particles makes it possible with a large degree of accuracy to estimate the condition of the body's lipid metabolism and the use of lipids as sources of energy.

If the formation of lipids is derived from carbohydrates or proteins, the glycerin precursor becomes an intermediate product of glycolysis - phosphodioxyacetone, fatty acids and cholesterol - acetylcooferment A, amino acids - some amino acids. Lipid synthesis requires large energy to activate the starting materials.

The main part of the decomposition of fat is absorbed from the cells of the intestinal epithelium in lymphatic system intestines, breast lymphatic duct and only then - in blood. A minor part of short-chain fatty acids and glycerin is capable of absorbed directly into the blood of the carrier vein.