Thank you

The site provides reference information for informational purposes only. Diagnosis and treatment of diseases must be carried out under the supervision of a specialist. All drugs have contraindications. Consultation with a specialist is required!

What kind of substances are lipids?

Lipids represent one of the groups of organic compounds that are of great importance for living organisms. According to their chemical structure, all lipids are divided into simple and complex. Simple lipids are made up of alcohol and bile acids, while complex lipids contain other atoms or compounds.

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

What is the difference between lipids and fats?

Basically, the term "lipids" comes from a Greek root meaning "fat", but there are still some differences between these definitions. Lipids are a larger group of substances, while fats refer to only certain types of lipids. A synonym for “fats” are “triglycerides,” which are obtained from a combination of glycerol alcohol 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 tissues of the body. Their molecules are present in any living cell, and without these substances life is simply impossible. There are many different lipids found in the human body. Each type or class of these compounds has its own functions. Many biological processes depend on the normal supply and formation of lipids.

From a biochemical point of view, lipids take part in the following important processes:

• energy production by the body;

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

Thus, lipids are vital chemical compounds. A significant portion of these substances enters the body with food. After this, 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 organism, but also in each living cell individually. In essence, a cell is a structural unit of a living organism. It is where assimilation and synthesis occurs ( education) certain substances. Some of these substances go to maintaining the life of the cell itself, some to cell division, and some to the needs of other cells and tissues.

In a living organism, lipids perform the following functions:

• energy;
• reserve;
• structural;
• transport;
• enzymatic;
• storing;
• signal;
• regulatory

Energy function

The energy function of lipids is reduced to their breakdown in the body, during which a large amount of energy is released. Living cells need this energy to maintain various processes ( respiration, growth, division, synthesis of new substances). Lipids enter the cell with blood flow and are deposited inside ( in the cytoplasm) in the form of small drops of fat. If necessary, these molecules are broken down and the cell receives energy.

Reserve ( storing) function

The reserve function is closely related to the energy function. In the form of fats inside cells, energy can be stored “in reserve” and released as needed. Special cells - adipocytes - are responsible for the accumulation of fats. Most of their volume is occupied by a large drop of fat. It is adipocytes that make up adipose tissue in the body. The largest reserves of adipose tissue are located in the subcutaneous fat, the greater and lesser omentum ( in the abdominal cavity). During prolonged fasting, adipose tissue gradually breaks down, as lipid reserves are used to obtain energy.

Also, adipose tissue deposited in subcutaneous fat provides thermal insulation. Tissues rich in lipids are generally poorer conductors of heat. This allows the body to maintain a constant body temperature and not cool down or overheat so quickly under different environmental conditions.

Structural and barrier functions ( membrane lipids)

Lipids play a huge role in the structure of living cells. In the human body, these substances form a special double layer that forms the cell wall. Thanks to this, a living cell can perform its functions and regulate metabolism with the external environment. Lipids that form the cell membrane also help maintain the shape of the cell.

Why do lipid monomers form a double layer ( bilayer)?

Monomers are chemical substances ( in this case – molecules), which are capable of combining to form more complex compounds. The cell wall consists of a double layer ( bilayer) lipids. Each molecule that forms this wall has two parts - hydrophobic ( not in contact with water) and hydrophilic ( in contact with water). The double layer is obtained due to the fact that the lipid molecules are deployed with hydrophilic parts inside and outside the cell. The hydrophobic parts practically touch, as they are located between the two layers. Other molecules may also be located in the depth of the lipid bilayer ( proteins, carbohydrates, complex molecular structures), which regulate the passage of substances through the cell wall.

Transport function

The transport function of lipids is of secondary importance in the body. Only some connections do this. For example, lipoproteins, consisting of lipids and proteins, transport certain substances in the blood from one organ to another. However, this function is rarely isolated, without considering it to be the main one for these substances.

Enzymatic function

In principle, lipids are not part of the enzymes involved in the breakdown of other substances. However, without lipids, organ cells will not be able to synthesize enzymes, the end product of vital activity. In addition, some lipids play a significant role in the absorption of dietary fats. Bile contains significant amounts of phospholipids and cholesterol. They neutralize excess pancreatic enzymes and prevent them from damaging intestinal cells. Dissolution also occurs in bile ( emulsification) exogenous lipids coming from food. Thus, lipids play a huge role in digestion and help in the work of other enzymes, although they are not enzymes themselves.

Signal function

Some complex lipids perform a signaling function in the body. It consists of maintaining various processes. For example, glycolipids in nerve cells take part in the transmission of nerve impulses from one nerve cell to another. In addition, signals within the cell itself are of great importance. She needs to “recognize” substances entering the blood in order to transport them inside.

Regulatory function

The regulatory function of lipids in the body is secondary. The lipids themselves in the blood have little effect on 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 ( adrenal hormones and sex hormones). They play an important role in metabolism, growth and development of the body, reproductive function, and affect the functioning of the immune system. Lipids are also part of prostaglandins. These substances are produced during inflammatory processes and affect certain processes in the nervous system ( for example, pain perception).

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

Biochemistry of lipids and their relationship with other substances ( proteins, carbohydrates, ATP, nucleic acids, amino acids, steroids)

Lipid metabolism is closely related to the metabolism of other substances in the body. First of all, this connection can be traced in human nutrition. Any food consists of proteins, carbohydrates and lipids, which must enter the body in certain proportions. In this case, a person will receive both enough energy and enough structural elements. Otherwise ( for example, with a lack of lipids) proteins and carbohydrates will be broken down to produce energy.

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

• Adenosine triphosphoric acid ( ATP). ATP is a unique unit of energy inside a cell. When lipids are broken down, part of the energy goes into the production of ATP molecules, and these molecules take part in all intracellular processes ( transport of substances, cell division, neutralization of toxins, etc.).
• Nucleic acids. Nucleic acids are structural elements of DNA and are found in the nuclei of living cells. The energy generated during the breakdown of fats is partially used for cell division. During division, new DNA chains are formed from nucleic acids.
• Amino acids. Amino acids are structural components of proteins. In combination with lipids, they form complex complexes, lipoproteins, responsible for the transport of substances in the body.
• Steroids. Steroids are a type of hormone that contains significant amounts of lipids. If lipids from food are poorly absorbed, the patient may experience problems with the endocrine system.

Thus, lipid metabolism in the body in any case must be considered in its entirety, from the point of view of its relationship with other substances.

Digestion and absorption of lipids ( metabolism, metabolism)

Digestion and absorption of lipids is the first stage in the metabolism of these substances. The main part of lipids enters the body with food. In the oral cavity, food is crushed and mixed with saliva. Next, the lump enters the stomach, where the chemical bonds are partially destroyed by hydrochloric acid. Also, some chemical bonds in lipids are destroyed by the enzyme lipase contained in saliva.

Lipids are insoluble in water, so they are not immediately broken down by enzymes in the duodenum. First, the so-called emulsification of fats occurs. After this, the chemical bonds are broken down by lipase coming from the pancreas. In principle, for each type of lipid, its own enzyme has now been identified, which is responsible for the breakdown and absorption of this substance. For example, phospholipase breaks down phospholipids, cholesterol esterase breaks down cholesterol compounds, etc. All these enzymes are contained in varying quantities in pancreatic juice.

The split lipid fragments are absorbed individually by the cells of the small intestine. In general, fat digestion is a very complex process that is regulated by many hormones and hormone-like substances.

What is lipid emulsification?

Emulsification is the incomplete dissolution of fatty substances in water. In the bolus of food entering the duodenum, fats are contained in the form of large droplets. This prevents them from interacting with enzymes. During the emulsification process, large fat droplets are “crushed” into smaller droplets. As a result, the contact area between fat droplets and surrounding water-soluble substances increases, and lipid breakdown becomes possible.

The process of emulsification of lipids in the digestive system takes place in several stages:

• At the first stage, the liver produces bile, which will emulsify fats. It contains salts of cholesterol and phospholipids, which interact with lipids and contribute to their “crushing” into small droplets.
• Bile secreted from the liver accumulates in the gallbladder. Here it is concentrated and released as needed.
• When consuming fatty foods, a signal is sent to the smooth muscles of the gallbladder to contract. As a result, a portion of bile is released through the bile ducts into the duodenum.
• In the duodenum, fats are actually emulsified and interact with pancreatic enzymes. Contractions in the walls of the small intestine facilitate this process by “mixing” the contents.

Some people may have trouble absorbing fat after having their gallbladder removed. Bile enters the duodenum continuously, directly from the liver, and there is not enough of it to emulsify the entire volume of lipids if too much is eaten.

Enzymes for lipid breakdown

To digest each substance, the body has its own enzymes. Their task is to break chemical bonds between molecules ( or between atoms in molecules) so that nutrients can be properly absorbed by the body. Different enzymes are responsible for breaking down different lipids. Most of them are contained in the juice secreted by the pancreas.

The following groups of enzymes are responsible for the breakdown of lipids:

• lipases;
• phospholipases;
• cholesterol esterase, etc.

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

The levels of most lipids in human blood are relatively constant. It can fluctuate within certain limits. This depends on the biological processes occurring in the body itself, and on a number of external factors. Regulation of blood lipid levels is a complex biological process in which many different organs and substances are involved.

The following substances play the greatest role in the absorption and maintenance of constant lipid levels:

• Enzymes. A number of pancreatic enzymes take part in the breakdown of lipids entering the body with food. With a lack of these enzymes, the level of lipids in the blood may decrease, since these substances simply will not be absorbed in the intestines.
• Bile acids and their salts. Bile contains bile acids and a number of their compounds, which contribute to the emulsification of lipids. Without these substances, normal absorption of lipids is also impossible.
• Vitamins. Vitamins have a complex strengthening effect on the body and also directly or indirectly affect lipid metabolism. For example, with a lack of vitamin A, cell regeneration in the mucous membranes deteriorates, and the digestion of substances in the intestines also slows down.
• Intracellular enzymes. The intestinal epithelial cells contain enzymes that, after absorption of fatty acids, convert them into transport forms and send them into the bloodstream.
• Hormones. A number of hormones affect metabolism in general. For example, high insulin levels can greatly affect blood lipid levels. That is why some standards have been revised for patients with diabetes. Thyroid hormones, glucocorticoid hormones, or norepinephrine can stimulate the breakdown of fat tissue to release energy.

Thus, maintaining normal levels of lipids in the blood is a very complex process, which is directly or indirectly influenced by various hormones, vitamins and other substances. During the diagnostic process, the doctor needs to determine at what stage this process was disrupted.

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

Metabolism is the totality of metabolic processes in the body. All metabolic processes can be divided into catabolic and anabolic. Catabolic processes include the breakdown and breakdown of substances. In relation to lipids, this is characterized by their hydrolysis ( breakdown into simpler substances) in the gastrointestinal tract. Anabolism combines biochemical reactions aimed at the formation of new, more complex substances.

Lipid biosynthesis occurs in the following tissues and cells:

• Intestinal epithelial cells. Absorption of fatty acids, cholesterol and other lipids occurs in the intestinal wall. Immediately after this, new transport forms of lipids are formed in these same cells, which enter the venous blood and are sent to the liver.
• Liver cells. In liver cells, some of the transport forms of lipids will disintegrate, and new substances are synthesized from them. For example, cholesterol and phospholipid compounds are formed here, which are then excreted in bile and contribute to normal digestion.
• Cells of other organs. Some lipids travel with the blood to other organs and tissues. Depending on the cell type, lipids are converted into a specific type of compound. All cells, one way or another, synthesize lipids to form the cell wall ( lipid bilayer). In the adrenal glands and gonads, steroid hormones are synthesized from some lipids.

The combination of the above processes constitutes lipid metabolism in the human body.

Resynthesis of lipids in the liver and other organs

Resynthesis is the process of formation of certain substances from simpler ones that were absorbed earlier. In the body, this process occurs in the internal environment of some cells. Resynthesis is necessary so that tissues and organs receive all the necessary types of lipids, and not just those consumed with food. Resynthesized lipids are called endogenous. The body spends energy on their formation.

At the first stage, lipid resynthesis occurs in the intestinal walls. Here, fatty acids ingested from food are converted into transport forms that are transported through the blood to the liver and other organs. Part of the resynthesized lipids will be delivered to the tissues; from the other part, substances necessary for life will be formed ( lipoproteins, bile, hormones, etc.), the excess is converted into adipose tissue and stored “in reserve.”

Are lipids part of the brain?

Lipids are a very important component of nerve cells, not only in the brain, but throughout the nervous system. As you know, nerve cells control various processes in the body by transmitting nerve impulses. In this case, all nerve pathways are “isolated” from each other so that the impulse comes to certain cells and does not affect other nerve pathways. This “isolation” is possible thanks to the myelin sheath of nerve cells. Myelin, which prevents the chaotic propagation of impulses, consists of approximately 75% lipids. As in cell membranes, here they form a double layer ( bilayer), which is wrapped several times around the nerve cell.

The myelin sheath in the nervous system contains the following lipids:

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

Some congenital lipid disorders may cause neurological problems. This is explained precisely by the thinning or interruption of the myelin sheath.

Lipid hormones

Lipids play an important structural role, including being present in the structure of many hormones. Hormones that contain fatty acids are called steroid hormones. In the body they are produced by the gonads and adrenal glands. Some of them are also present in adipose tissue cells. Steroid hormones take part in the regulation of many vital processes. Their imbalance can affect body weight, the ability to conceive a child, the development of any inflammatory processes, and the functioning of the immune system. The key to normal production of steroid hormones is a balanced intake of lipids.

Lipids are part of the following vital hormones:

• corticosteroids ( cortisol, aldosterone, hydrocortisone, etc.);
• male sex hormones - androgens ( androstenedione, dihydrotestosterone, etc.);
• female sex hormones - estrogens ( estriol, estradiol, etc.).

Thus, a lack of certain fatty acids in food can seriously affect the functioning of the endocrine system.

The role of lipids for skin and hair

Lipids are of great importance for the health of the skin and its appendages ( hair and nails). The skin contains so-called sebaceous glands, which secrete a certain amount of secretion rich in fats onto the surface. This substance performs many useful functions.

Lipids are important for hair and skin 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 ( secreted substance) sebaceous glands moisturize the skin;
• Thanks to fats, the firmness, elasticity and smoothness of the skin is maintained;
• a small amount of lipids on the surface of the hair gives it a healthy shine;
• the lipid layer on the surface of the skin protects it from the aggressive effects of external factors ( cold, sun rays, microbes on the surface of the skin, etc.).

Lipids enter skin cells, as well as hair follicles, with the blood. Thus, proper nutrition ensures healthy skin and hair. The use of shampoos and creams containing lipids ( especially essential fatty acids) is also important because some of these substances will be absorbed from the surface of the cells.

Classification of lipids

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

Biology and medicine have their own 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 that enter the body from the external environment. The largest amount of exogenous lipids enters the body with food, but there are other routes. For example, when using various cosmetics or medications, the body can also receive a certain amount of lipids. Their action will be predominantly local.

After entering the body, all exogenous lipids are broken down and absorbed by living cells. Here, from their structural components, other lipid compounds that the body needs will be formed. These lipids, synthesized by one's own cells, are called endogenous. They may have a completely different structure and function, but they consist of the same “structural components” that entered the body with exogenous lipids. That is why, with a lack of certain types of fats in food, various diseases can develop. Some components of complex lipids cannot be synthesized by the body independently, which affects the course of certain biological processes.

Fatty acids

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

In nature, fatty acids are found in a variety of substances - from petroleum to vegetable oils. They enter the human body mainly through food. Each acid is a structural component for specific cells, enzymes or compounds. Once absorbed, the body converts it and uses it 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, etc.).

In the human body, fatty acids can be stored in adipose tissue as triglycerides or circulate in the blood. They are found in the blood both in free form and in the form of compounds ( various fractions of lipoproteins).

Saturated and unsaturated fatty acids

All fatty acids according to their chemical structure are divided into saturated and unsaturated. Saturated acids are less beneficial for the body, and some of them are even harmful. This is explained by the fact that there are no double bonds in the molecule of these substances. These are chemically stable compounds and are less easily absorbed by the body. Currently, the connection between some saturated fatty acids and the development of atherosclerosis has been proven.

Unsaturated fatty acids are divided into two large groups:

• Monounsaturated. These acids have one double bond in their structure and are therefore more active. It is believed that eating them can lower cholesterol levels and prevent the development of atherosclerosis. The greatest amount of monounsaturated fatty acids is found in a number of plants ( avocado, olives, pistachios, hazelnuts) and, accordingly, in oils obtained from these plants.
• Polyunsaturated. Polyunsaturated fatty acids have several double bonds in their structure. A distinctive feature of these substances is that the human body is not able to synthesize them. In other words, if the body does not receive polyunsaturated fatty acids from food, over time this will inevitably lead to certain disorders. The best sources of these acids are seafood, soybean and flaxseed oil, sesame seeds, poppy seeds, wheat germ, etc.

Phospholipids

Phospholipids are complex lipids containing a phosphoric acid residue. These substances, along with cholesterol, are the main components of cell membranes. These substances also take part in the transport of other lipids in the body. From a medical point of view, phospholipids can also play a signaling role. For example, they are part of bile, as they promote emulsification ( dissolution) other fats. Depending on which substance is more in bile, cholesterol or phospholipids, you can determine the risk of developing cholelithiasis.

Glycerol and triglycerides

In terms of its chemical structure, glycerol is not a lipid, but it is an important structural component of triglycerides. This is a group of lipids that play a huge role in the human body. The most important function of these substances is to supply energy. Triglycerides that enter the body with food are broken down into glycerol and fatty acids. As a result, a very large amount of energy is released, which goes to muscle work ( skeletal muscles, cardiac muscles, etc.).

Adipose tissue in the human body is represented mainly by triglycerides. Most of these substances, before being deposited in adipose tissue, undergo some chemical transformations 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 certain pathologies. First of all, we are talking about atherosclerosis. Beta lipoproteins transport cholesterol from one cell to another, but due to the structural features of the molecules, this cholesterol often “gets stuck” in the walls of blood vessels, forming atherosclerotic plaques and preventing normal blood flow. Before use, you should consult a specialist.

Lipid metabolism in the body (fat metabolism)

Biochemistry of lipid metabolism

Fat metabolism is the totality of processes of digestion and absorption of neutral fats (triglycerides) and their breakdown products in the gastrointestinal tract, intermediate metabolism of fats and fatty acids and the removal of fats, as well as their metabolic products from the body. The terms “fat metabolism” and “lipid metabolism” are often used interchangeably, because components of the tissues of animals and plants include neutral fats and fat-like compounds, collectively called lipids .

According to average statistics, an adult’s body receives an average of 70 g of fats of animal and plant origin with food every day. In the oral cavity, fats do not undergo any changes, because saliva does not contain fat-digesting enzymes. The partial breakdown of fats into glycerol and fatty acids begins in the stomach. However, it proceeds at a low speed, since in the gastric juice of an adult the activity of the lipase enzyme, which catalyzes the hydrolytic breakdown of fats, is extremely low, and the pH value of the gastric juice is far from optimal for the action of this enzyme (the optimal pH value for gastric lipase is within 5.5 --7.5 pH units). In addition, there are no conditions in the stomach for the emulsification of fats, and lipase can only actively hydrolyze fat in the form of a fat emulsion. Therefore, in adults, fats, which make up the bulk of dietary fat, do not undergo any special changes in the stomach.

However, in general, gastric digestion greatly facilitates the subsequent digestion of fat in the intestines. In the stomach, partial destruction of lipoprotein complexes of food cell membranes occurs, which makes fats more accessible for the subsequent action of pancreatic juice lipase on them. In addition, even a small breakdown of fats in the stomach leads to the appearance of free fatty acids, which, without being absorbed in the stomach, enter the intestines and there contribute to the emulsification of fat.

Bile acids that enter the duodenum with bile have the most powerful emulsifying effect. A certain amount of gastric juice containing hydrochloric acid is introduced into the duodenum along with the food mass, which in the duodenum is neutralized mainly by bicarbonates contained in pancreatic and intestinal juice and bile. The bubbles of carbon dioxide formed during the reaction of bicarbonates with hydrochloric acid loosen the food pulp and facilitate its more complete mixing with digestive juices. At the same time, fat emulsification begins. Bile salts are adsorbed in the presence of small amounts of free fatty acids and monoglycerides on the surface of fat droplets in the form of a thin film that prevents the merging of these droplets. In addition, bile salts, by reducing the surface tension at the water-fat interface, promote the fragmentation of large fat droplets into smaller ones. Conditions are created for the formation of a thin and stable fat emulsion with particles with a diameter of 0.5 microns or less. As a result of emulsification, the surface of fat droplets sharply increases, which increases the area of ​​their interaction with lipase, i.e. accelerates enzymatic hydrolysis and absorption.

The main part of dietary fats undergoes breakdown in the upper parts of the small intestine under the action of pancreatic juice lipase. The so-called pancreatic lipase exhibits optimal action at a pH of about 8.0.

Intestinal juice contains lipase, which catalyzes the hydrolytic breakdown of monoglycerides and has no effect on di- and triglycerides. Its activity, however, is low, so practically the main products formed in the intestines during the breakdown of dietary fats are fatty acids and β-monoglycerides.

Absorption of fats, like other lipids, occurs in the proximal part of the small intestine. The limiting factor for this process, apparently, is the size of the fat emulsion droplets, the diameter of which should not exceed 0.5 microns. However, the bulk of the fat is absorbed only after it is broken down by pancreatic lipase into fatty acids and monoglycerides. Absorption of these compounds occurs with the participation of bile.

Small amounts of glycerol formed during the digestion of fats are easily absorbed in the small intestine. Glycerol is partially converted into b-glycerophosphate in the cells of the intestinal epithelium, and partially enters the bloodstream. Fatty acids with a short carbon chain (less than 10 carbon atoms) are also easily absorbed in the intestine and enter the bloodstream, bypassing any transformations in the intestinal wall.

The products of the breakdown of dietary fats, formed in the intestine and entering its wall, are used for the resynthesis of triglycerides. The biological meaning of this process is that fats that are specific to humans and qualitatively different from dietary fat are synthesized in the intestinal wall. However, the body's ability to synthesize body-specific fat is limited. Foreign fats can also be deposited in its fat depots when they are increased in the body.

The mechanism of resynthesis of triglycerides in the cells of the intestinal wall is generally identical to their biosynthesis in other tissues.

2 hours after eating a meal containing fats, so-called nutritional hyperlipemia develops, characterized by an increase in the concentration of triglycerides in the blood. After eating too fatty foods, the blood plasma takes on a milky color, which is explained by the presence of a large number of chylomicrons (a class of lipoproteins formed in the small intestine during the absorption of exogenous lipids). The peak of nutritional hyperlipemia is observed 4-6 hours after ingestion of fatty foods, and after 10-12 hours the fat content in the blood serum returns to normal, i.e. it is 0.55-1.65 mmol/l, or 50 --150 mg/100 ml. By this time, in healthy people, chylomicrons completely disappear from the blood plasma. Therefore, taking blood for research in general, and especially to determine its lipid content, should be carried out on an empty stomach, 14 hours after the last meal.

The liver and adipose tissue play the most important role in the further fate of chylomicrons. It is assumed that hydrolysis of chylomicron triglycerides can occur both inside liver cells and on their surface. Liver cells have enzyme systems that catalyze the conversion of glycerol into b-glycerophosphate, and non-esterified fatty acids (NEFA) into the corresponding acyl-CoAs, which are either oxidized in the liver to release energy or are used for the synthesis of triglycerides and phospholipids. Synthesized triglycerides and partially phospholipids are used to form very low-density lipoproteins (pre-β-lipoproteins), which are secreted by the liver and released into the blood. Very low density lipoproteins (in this form, from 25 to 50 g of triglycerides are transported in the human body per day) are the main transport form of endogenous triglycerides.

Due to their large size, chylomicrons are not able to penetrate the cells of adipose tissue; therefore, triglycerides of chylomicrons undergo hydrolysis on the surface of the endothelium of capillaries penetrating adipose tissue under the action of the enzyme lipoprotein lipase. As a result of the cleavage of chylomicron triglycerides (as well as triglycerides of pre-β-lipoproteins) by lipoprotein lipase, free fatty acids and glycerol are formed. Some of these fatty acids pass into fat cells, and some bind to serum albumin. Glycerol, as well as particles of chylomicrons and pre-b-lipoproteins remaining after the breakdown of their triglyceride component and called remnants, leave the adipose tissue with the bloodstream. In the liver, remnants undergo complete disintegration.

After penetration into fat cells, fatty acids are converted into their metabolically active forms (acyl-CoA) and react with b-glycerophosphate, which is formed in adipose tissue from glucose. As a result of this interaction, triglycerides are resynthesized, which replenish the total supply of triglycerides in adipose tissue.

The breakdown of triglycerides of chylomicrons in the blood capillaries of adipose tissue and liver leads to the actual disappearance of chylomicrons themselves and is accompanied by clearing of the blood plasma, i.e. loss of milky color. This clearing can be accelerated by heparin. Intermediate fat metabolism includes the following processes: mobilization of fatty acids from fat depots and their oxidation, biosynthesis of fatty acids and triglycerides and conversion of unsaturated fatty acids.

Human adipose tissue contains large amounts of fat, mainly in the form of triglycerides. which perform the same function in fat metabolism as liver glycogen does in carbohydrate metabolism. Triglyceride stores can be consumed during fasting, physical work, and other conditions that require high energy expenditure. The reserves of these substances are replenished after food consumption. The body of a healthy person contains about 15 kg of triglycerides (140,000 kcal) and only 0.35 kg of glycogen (1410 kcal).

Triglycerides from adipose tissue, with an average adult energy requirement of 3500 kcal per day, are theoretically sufficient to meet the body's 40-day energy requirement.

Triglycerides in adipose tissue undergo hydrolysis (lipolysis) under the action of lipase enzymes. Adipose tissue contains several lipases, of which the most important are the so-called hormone-sensitive lipase (triglyceride lipase), diglyceride lipase and monoglyceride lipase. Resynthesized triglycerides remain in adipose tissue, thus contributing to the preservation of its total reserves.

Increased lipolysis in adipose tissue is accompanied by an increase in the concentration of free fatty acids in the blood. The transport of fatty acids is very intensive: from 50 to 150 g of fatty acids are transferred in the human body per day.

Fatty acids bound to albumin (simple water-soluble proteins exhibiting high binding capacity) enter the bloodstream into organs and tissues, where they undergo beta-oxidation (fatty acid degradation reaction cycle), and then oxidation in the tricarboxylic acid cycle (Krebs cycle) . About 30% of fatty acids are retained in the liver even after blood passes through it once. Some fatty acids not used for triglyceride synthesis are oxidized in the liver to ketone bodies. Ketone bodies, without undergoing further transformations in the liver, enter through the bloodstream into other organs and tissues (muscles, heart, etc.), where they are oxidized to CO 2 and H 2 O.

Triglycerides are synthesized in many organs and tissues, but the most important role in this regard is played by the liver, intestinal wall and adipose tissue. In the intestinal wall, monoglycerides, which come in large quantities from the intestine after the breakdown of dietary fats, are used for the resynthesis of triglycerides. In this case, the reactions are carried out in the following sequence: monoglyceride + fatty acid acyl-CoA (activated acetic acid) > diglyceride; diglyceride + fatty acid acyl-CoA > triglyceride.

Normally, the amount of triglycerides and fatty acids released from the human body unchanged does not exceed 5% of the amount of fat taken with food. Basically, the removal of fat and fatty acids occurs through the skin with the secretions of the sebaceous and sweat glands. The secretion of sweat glands contains mainly water-soluble fatty acids with a short carbon chain; the secretion of the sebaceous glands is dominated by neutral fats, cholesterol esters with higher fatty acids and free higher fatty acids, the removal of which causes the unpleasant odor of these secretions. A small amount of fat is released as part of the sloughing cells of the epidermis.

In case of skin diseases accompanied by increased secretion of the sebaceous glands (seborrhea, psoriasis, acne, etc.) or increased keratinization and desquamation of epithelial cells, the excretion of fat and fatty acids through the skin increases significantly.

During the digestion of fats in the gastrointestinal tract, about 98% of the fatty acids that make up dietary fats and almost all of the resulting glycerol are absorbed. The remaining small amount of fatty acids is excreted unchanged in the feces or is converted under the influence of intestinal microbial flora. In general, a person excretes about 5 g of fatty acids in feces per day, and at least half of them are entirely of microbial origin. A small amount of short-chain fatty acids (acetic, butyric, valeric), as well as β-hydroxybutyric and acetoacetic acids are excreted in the urine, the amount of which in daily urine ranges from 3 to 15 mg. The appearance of higher fatty acids in the urine is observed in lipoid nephrosis, fractures of long bones, in diseases of the urinary tract accompanied by increased desquamation of the epithelium, and in conditions associated with the appearance of albumin in the urine (albuminuria).

A schematic representation of the key processes in the lipid metabolism system is presented in Appendix A.

Lipid metabolism is a fat metabolism that takes place in the organs of the digestive tract with the participation of enzymes produced by the pancreas. If this process is disrupted, symptoms may vary depending on the nature of the failure - an increase or decrease in lipid levels. With this dysfunction, the amount of lipoproteins is examined, since they can identify the risk of developing cardiovascular diseases. Treatment is determined strictly by the doctor based on the results obtained.

What is lipid metabolism?

When entering the body along with food, fats undergo primary processing in the stomach. However, complete digestion does not occur in this environment, since it is highly acidic but lacks bile acids.

Lipid metabolism scheme

When they enter the duodenum, which contains bile acids, the lipids undergo emulsification. This process can be described as partial mixing with water. Since the environment in the intestines is slightly alkaline, the acidic contents of the stomach are loosened under the influence of released gas bubbles, which are a product of the neutralization reaction.

The pancreas synthesizes a specific enzyme called lipase. It is he who acts on fat molecules, breaking them down into two components: fatty acids and glycerol. Typically, fats are transformed into polyglycerides and monoglycerides.

Subsequently, these substances enter the epithelium of the intestinal wall, where the biosynthesis of lipids necessary for the human body occurs. They then combine with proteins to form chylomicrons (a class of lipoproteins), after which they are distributed throughout the body along with the flow of lymph and blood.

In body tissues, the reverse process of obtaining fats from blood chylomicrons occurs. The most active biosynthesis occurs in the fat layer and liver.

Symptoms of a disrupted process

If lipid metabolism is disturbed in the human body, the result is various diseases with characteristic external and internal signs. The problem can only be identified after laboratory tests.

Impaired fat metabolism can manifest itself in the following symptoms of elevated lipid levels:

• the appearance of fatty deposits in the corners of the eyes;
• increased volume of the liver and spleen;
• increased body mass index;
• manifestations characteristic of nephrosis, atherosclerosis, endocrine diseases;
• increased vascular tone;
• formation of xanthomas and xanthelasmas of any localization on the skin and tendons. The first are nodular neoplasms containing cholesterol. They affect the palms, feet, chest, face and shoulders. The second group also represents cholesterol neoplasms, which have a yellow tint and appear on other areas of the skin.

When lipid levels are low, the following symptoms appear:

• weight loss;
• separation of the nail plates;
• hair loss;
• nephrosis;
• disorders of the menstrual cycle and reproductive functions in women.

Lipidogram

Cholesterol moves in the blood along with proteins. There are several types of lipid complexes:

1. 1. Low-density lipoproteins (LDL). They are the most harmful fraction of lipids in the blood, with a high ability to form atherosclerotic plaques.
2. 2. High density lipoproteins (HDL). They have the opposite effect, preventing the formation of deposits. They transport free cholesterol to liver cells, where it is subsequently processed.
3. 3. Very low density lipoproteins (VLDL). They are the same harmful atherogenic compounds as LDL.
4. 4. Triglycerides. They are fatty compounds that are a source of energy for cells. When they are excessive in the blood, the vessels are predisposed to atherosclerosis.

Assessing the risk of developing cardiovascular diseases by cholesterol levels is not effective if a person has a disorder of lipid metabolism. With a predominance of atherogenic fractions over conditionally harmless ones (HDL), even with normal cholesterol levels, the likelihood of developing atherosclerosis seriously increases. Therefore, if fat metabolism is disturbed, a lipid profile should be performed, that is, blood biochemistry (analysis) should be performed to determine the amount of lipids.

Based on the obtained indicators, the atherogenicity coefficient is calculated. It shows the ratio of atherogenic lipoproteins to non-atherogenic ones. Defined as follows:

Formula for calculating the atherogenic coefficient

Normally, KA should be less than 3. If it is between 3 and 4, then there is a high risk of developing atherosclerosis. When the value is exceeded 4, progression of the disease is observed.

How is fat formed in the human body?

The human body can form lipids or triglycerides not only from fats coming from food, but also from carbohydrates and proteins. Fats from incoming food enter the gastrointestinal tract, are absorbed in the small intestine, undergo a transformation process and are broken down into fatty acids and glycerol. There are also internal, endogenous fats that are synthesized in the liver. Fatty acids are a source of large amounts of energy, being a kind of body “fuel”.

They are absorbed into the blood and, with the help of special transport forms - lipoproteins, chylomicrons, are carried to various organs and tissues. Fatty acids can again be used for the synthesis of triglycerides and fat, and if they are in excess, they can be stored in the liver and in adipose tissue cells - adipocytes. It is adipocytes with a large supply of triglycerides that create discomfort for a person and manifest themselves as excess deposits of subcutaneous fat and excess weight. Fat deposits can also be formed from carbohydrates.

Glucose and fructose entering the blood with the help of the hormone insulin can be deposited in the form of triglycerides in the liver and cells. Proteins supplied with food are also capable of being transformed into triglycerides through a cascade of transformations: proteins are broken down into amino acids, absorbed into the blood, penetrate into the liver, converted into glucose and, under the action of insulin, become triglycerides stored in adipocytes. This is a very simplified way to imagine the process of lipid formation in the human body.

2 Functions of lipids in the body

The role of fats in the human body is difficult to overestimate. They are:

• the main energy source in the body;
• building material for cell membranes, organelles, a number of hormones and enzymes;
• a protective “cushion” for internal organs.

Fat cells carry out thermoregulation, increase the body's resistance to infection, secrete hormone-like substances - cytokines, and also regulate metabolic processes.

3 How are fats used?

Triglycerides stored “in reserve” can leave adipocytes and be used for cell needs when they receive insufficient energy or require structural material to build membranes. Hormones of the body that have a lipolytic effect - adrenaline, glucagon, somatotropin, cortisol, thyroid hormones - send a signal to adipocytes - lipolysis or the process of fat breakdown occurs.

Having received “instructions” from hormones, triglycerides are broken down into fatty acids and glycerol. Fatty acids are transported into the blood using carriers called lipoproteins. Lipoproteins in the blood interact with cell receptors, which break down lipoproteins and take fatty acids for further oxidation and use: building membranes or producing energy. Lipolysis can be activated under stress and excessive physical activity.

4 Why is lipid metabolism disrupted?

Dyslipidemia or a disorder of lipid metabolism is a condition in which, for various reasons, there is a change in the content of lipids in the blood (increase or decrease), or the appearance of pathological lipoproteins. The condition is caused by pathological processes in the synthesis, breakdown of fats or their inadequate removal from the blood. Problems in lipid metabolism can lead to excess fats in the blood - hyperlipidemia.

According to research, this condition is typical for 40% of the adult population, and occurs even in childhood.

Disorders of lipid metabolism can be provoked by a number of factors that trigger pathological processes of imbalance in the supply and utilization of lipids. Risk factors include:

• physical inactivity or a sedentary lifestyle,
• smoking,
• alcohol abuse,
• increased activity of thyroid hormones,
• excess body weight,
• diseases that provoke lipid metabolic disorders.

5 Primary disorders of lipid metabolism

All lipid metabolism disorders are classified into primary and secondary. Primary ones are caused by genetic defects and are hereditary in nature. There are several forms of primary disorders in lipid metabolism, the most common being familial hypercholesterolemia. This condition is caused by a defect in the gene encoding the synthesis and function of receptors that bind to certain lipoproteins. There are several forms of pathology (homo- and heterozygous), they are united by the hereditary nature of the disease, high cholesterol levels from birth, early development of atherosclerosis and ischemic heart disease.

A doctor may suspect hereditary dyslipoproteinemia in a patient if:

• early myocardial infarction;
• significant damage to blood vessels by the atherosclerotic process at a young age;
• available data on the incidence of coronary artery disease and cardiovascular accidents in close relatives at a young age.

6 Secondary disorders of lipid metabolism

These lipid metabolism disorders develop as a consequence of many diseases, as well as as a result of the use of certain medications.

Causes of high blood lipids:

• diabetes mellitus,
• obesity,
• hypothyroidism,
• taking medications: progesterone, thiazides, estrogens, glucocorticoids,
• chronic renal failure,
• stress.

Reasons for low lipid levels:

• malabsorption syndrome,
• reduced, insufficient nutrition,
• tuberculosis,
• chronic liver diseases,
• AIDS.

Dyslipidemia of secondary origin is very often observed in type 2 diabetes mellitus. It is always accompanied by atherosclerosis - changes in the walls of blood vessels with the deposition of “plaques” of excess cholesterol and other lipid fractions on them. Among patients with diabetes, the most common cause of death is coronary artery disease caused by atherosclerotic disorders.

7 Consequences of high blood lipids

Excessively “fatty” blood is enemy number 1 for the body. Excessive amounts of lipid fractions, as well as defects in their utilization, inevitably lead to the fact that “all the excess” settles on the vascular wall with the formation of atherosclerotic plaques. Metabolic lipid disorders lead to the development of atherosclerosis, which means that in such patients the risk of developing coronary heart disease, stroke, and heart rhythm disturbances increases many times.

8 Signs indicating lipid metabolism disorders

An experienced physician may suspect dyslipidemia in a patient upon examination. External signs indicating existing advanced violations will be:

• multiple yellowish formations - xanthomas, located on the torso, abdomen, forehead skin, as well as xanthelasmas - yellow spots on the eyelids;
• Men may experience early graying of hair on the head and chest;
• matte ring around the edge of the iris.

All external signs are a relative indication of a lipid metabolism disorder, and to confirm it, a set of laboratory and instrumental studies is required to confirm the doctor’s assumptions.

9 Diagnosis of lipid metabolism disorders

There is an examination program to identify dyslipidemia, which includes:

• general blood test, urine test,
• BAC: determination of total cholesterol, TG, LDL cholesterol, VLDL, HDL, ASAT, ALAT, bilirubin, protein, protein fractions, urea, alkaline phosphatase,
• determining blood glucose, and if there is a tendency to increase, performing a glucose tolerance test,
• determination of abdominal circumference, Quetelet index,
• blood pressure measurement,
• Examination of the vessels of the fundus,
• EchoCG,
• radiography of the OGK.

This is a general list of studies, which, in case of lipid metabolism disorders, can be expanded and supplemented at the discretion of the doctor.

10 Treatment of lipid metabolism disorders

Therapy for secondary dyslipidemia is aimed, first of all, at eliminating the underlying disease that caused the disorder of lipid metabolism. Correction of glucose levels in diabetes mellitus, normalization of body weight in obesity, treatment of absorption disorders and in the gastrointestinal tract are guaranteed to improve lipid metabolism. Elimination of risk factors and a lipid-lowering diet for lipid metabolism disorders is the most important part on the path to recovery.

Patients should forget about smoking, stop drinking alcohol, lead an active lifestyle and combat physical inactivity. Food should be enriched with PUFAs (they contain liquid vegetable oils, fish, seafood), and the overall consumption of fats and foods containing saturated fats (butter, eggs, cream, animal fat) should be reduced. Drug therapy for lipid metabolism disorders includes taking statins, fibrates, nicotinic acid, and bile acid sequestrants according to indications.

The YouTube ID of T1sovCwX-Z0?rel=0 is invalid.

>> Digestion of fats, regulation of metabolism

Metabolism of fats (lipids) in the human body

Fat (lipid) metabolism in the human body consists of three stages

1. Digestion and absorption of fats in the stomach and intestines

2. Intermediate metabolism of fats in the body

3. Excretion of fats and their metabolic products from the body.

Fats are part of a large group of organic compounds - lipids, therefore the concepts of “fat metabolism” and “lipid metabolism” are synonymous.

An adult's body receives about 70 grams of fats of animal and plant origin per day. Fat breakdown does not occur in the oral cavity, since saliva does not contain the corresponding enzymes. Partial breakdown of fats into components (glycerol, fatty acids) begins in the stomach, but this process is slow for the following reasons:

1. in the gastric juice of an adult, the activity of the enzyme (lipase) for the breakdown of fats is very low,

2. the acid-base balance in the stomach is not optimal for the action of this enzyme,

3. in the stomach there are no conditions for emulsification (splitting into small droplets) of fats, and lipase actively breaks down fats only in the composition of a fat emulsion.

Therefore, in an adult, most of the fat passes through the stomach without significant changes.

Unlike adults, in children the breakdown of fats in the stomach occurs much more actively.

The main part of dietary lipids undergoes breakdown in the upper part of the small intestine, under the influence of pancreatic juice.

Successful breakdown of fats is possible if they first break down into small droplets. This occurs under the influence of bile acids entering the duodenum with bile. As a result of emulsification, the surface of fats sharply increases, which facilitates their interaction with lipase.

Absorption of fats and other lipids occurs in the small intestine. Together with the products of fat breakdown, fat-soluble acids (A, D, E, K) enter the body.

The synthesis of fats specific to a given organism occurs in the cells of the intestinal wall. Subsequently, the newly created fats enter the lymphatic system, and then into the blood. The maximum fat content in the blood plasma occurs between 4 and 6 hours after eating a fatty meal. After 10 - 12 hours, the fat concentration returns to normal.

The liver takes an active part in fat metabolism. In the liver, some of the newly formed fats are oxidized to form the energy necessary for the body’s functioning. The other part of the fats is converted into a form convenient for transportation and enters the blood. Thus, from 25 to 50 grams of fat are transferred per day. Fats that the body does not immediately use are carried through the bloodstream into fat cells, where they are stored as reserves. These compounds can be used during fasting, exercise, and so on.

Fats are an important source of energy for our body. During short-term and sudden loads, the energy of glycogen, which is located in the muscles, is first used. If the load on the body does not stop, then the breakdown of fats begins.

From here it is necessary to conclude that if you want to get rid of extra pounds through physical activity, it is necessary that these activities be long enough for at least 30 - 40 minutes.

Fat metabolism is very closely related to carbohydrate metabolism. With an excess of carbohydrates in the body, fat metabolism slows down, and work goes only in the direction of synthesizing new fats and storing them in reserve. If there is a lack of carbohydrates in food, on the contrary, the breakdown of fats from the fat reserve is activated. From this we can conclude that nutrition for weight loss should limit (within reasonable limits) not only the consumption of fats, but also carbohydrates.

Most of the fats we eat are used by our body or stored in reserve. Under normal conditions, only 5% of fats are excreted from our body, this is done with the help of the sebaceous and sweat glands.

Regulation of fat metabolism

Regulation of fat metabolism in the body occurs under the guidance of the central nervous system. Our emotions have a very strong influence on fat metabolism. Under the influence of various strong emotions, substances enter the bloodstream that activate or slow down fat metabolism in the body. For these reasons, one must eat in a calm state of consciousness.

Disorders of fat metabolism can occur with a regular lack of vitamins A and B in food.

The physicochemical properties of fat in the human body depend on the type of fat supplied with food. For example, if a person’s main source of fat is vegetable oils (corn, olive, sunflower), then the fat in the body will have a more liquid consistency. If animal fats (lamb, pork fat) predominate in human food, then fats more similar to animal fat (hard consistency with a high melting point) will be deposited in the body. There is experimental confirmation of this fact.

How to remove trans fatty acids from the body

One of the most important tasks that modern man faces is how to cleanse his own body of toxins and poisons that have accumulated “thanks to” poor quality daily nutrition. A significant role in polluting the body is played by trans fats, which are abundantly supplied with daily food and over time greatly inhibit the functioning of internal organs.

Basically, trans fatty acids are eliminated from the body due to the ability of cells to renew. Some cells die and new ones appear in their place. If there are cells in the body whose membranes consist of trans-fatty acids, then after they die, new cells may appear in their place, the membranes of which consist of high-quality fatty acids. This happens if a person excludes foods containing trans fatty acids from the diet.

To ensure that as little trans fatty acids as possible penetrate cell membranes, you need to increase the amount of Omega-3 fatty acids you consume daily. By consuming foods containing such oils and fats, you can ensure that the membranes of nerve cells have the correct structure, which will have a positive effect on the functioning of the brain and nervous system.

We must remember that during heat treatment, fats can decompose to form irritating and harmful substances. Overheating fats reduces their nutritional and biological value.

Additional articles with useful information

Why do humans need fats?

The lack of fats in food significantly undermines a person’s health, and if healthy fats are present in the diet, then a person’s life becomes much easier by increasing physical and mental performance.

Description of the types of obesity and methods of treating this disease

Obesity has recently become increasingly widespread among the world's population, and this disease requires long-term and systemic treatment.