Determination of blood lipid profile indices is necessary for the diagnosis, treatment and prevention of cardiovascular diseases. The most important mechanism for the development of such a pathology is the formation of atherosclerotic plaques on the inner wall of blood vessels. Plaques are collections of fatty compounds (cholesterol and triglycerides) and fibrin. The higher the concentration of lipids in the blood, the more likely the appearance of atherosclerosis. Therefore, it is necessary to systematically take a blood test for lipids (lipid profile), this will help to timely identify deviations of fat metabolism from the norm.
Lipidogram - a study that determines the level of lipids of various fractions
Atherosclerosis is dangerous with a high probability of complications - stroke, myocardial infarction, gangrene of the lower extremities. These diseases often end in the patient's disability, and in some cases, death.
The role of lipids
Lipid functions:
- Structural. Glycolipids, phospholipids, cholesterol are the most important components of cell membranes.
- Heat insulating and protective. Excess fat is deposited in the subcutaneous fat, reducing heat loss and protecting internal organs. When needed, the body uses the lipid reserve for energy and simple compounds.
- Regulatory. Cholesterol is necessary for the synthesis of adrenal steroid hormones, sex hormones, vitamin D, bile acids, is part of the myelin sheaths of the brain, and is needed for the normal functioning of serotonin receptors.
Lipidogram
A lipidogram can be prescribed by a doctor both in case of suspicion of an existing pathology, and for prophylactic purposes, for example, during medical examination. It includes several indicators that allow you to fully assess the state of fat metabolism in the body.
Lipid profile indicators:
- Total cholesterol (TC). This is the most important indicator of the blood lipid spectrum, includes free cholesterol, as well as cholesterol contained in lipoproteins and associated with fatty acids. A significant part of cholesterol is synthesized by the liver, intestines, sex glands, only 1/5 of the TC comes from food. With normally functioning mechanisms of lipid metabolism, a small deficiency or excess of cholesterol supplied with food is compensated by an increase or decrease in its synthesis in the body. Therefore, hypercholesterolemia is most often caused not by an excessive intake of cholesterol with food, but by a malfunction of the process of fat metabolism.
- High-density lipoproteins (HDL). This indicator has an inverse relationship with the likelihood of developing atherosclerosis - an increased level of HDL is considered an antiatherogenic factor. HDL transports cholesterol to the liver where it is utilized. Women have higher HDL levels than men.
- Low density lipoprotein (LDL). LDL cholesterol transports cholesterol from the liver to tissues, otherwise known as "bad" cholesterol. This is due to the fact that LDL can form atherosclerotic plaques that narrow the lumen of blood vessels.
This is what the LDL particle looks like.
- Very low density lipoproteins (VLDL). The main function of this group of particles, heterogeneous in size and composition, is the transport of triglycerides from the liver to the tissue. A high concentration of VLDL in the blood leads to clouding of the serum (chyle), and the possibility of atherosclerotic plaques also increases, especially in patients with diabetes mellitus and kidney pathologies.
- Triglycerides (TG). Like cholesterol, triglycerides are carried along the bloodstream as part of lipoproteins. Therefore, an increase in the concentration of TG in the blood is always accompanied by an increase in cholesterol levels. Triglycerides are considered the main source of energy for cells.
- Atherogenic coefficient. It allows you to assess the risk of developing vascular pathology and is a kind of result of the lipid profile. To determine the indicator, you need to know the value of OH and HDL.
Atherogenic coefficient = (OH - HDL) / HDL
Optimal values of the blood lipid profile
| Floor | Indicator, mmol / l | |||||
| OH | HDL | LDL | VLDL | TG | CA | |
| Male | 3,21 — 6,32 | 0,78 — 1,63 | 1,71 — 4,27 | 0,26 — 1,4 | 0,5 — 2,81 | 2,2 — 3,5 |
| Female | 3,16 — 5,75 | 0,85 — 2,15 | 1,48 — 4,25 | 0,41 — 1,63 | ||
It should be borne in mind that the value of the measured indicators may vary depending on the units of measurement, the analysis methodology. Normal values also vary depending on the age of the patient, the above values are averaged for persons 20 - 30 years old. The norm of cholesterol and LDL in men after 30 years of age tends to increase. In women, the indicators increase sharply with the onset of menopause, this is due to the cessation of the antiatherogenic activity of the ovaries. The decoding of the lipid profile must be carried out by a specialist, taking into account the individual characteristics of a person.
A study of the level of lipids in the blood can be prescribed by a doctor to diagnose dyslipidemias, to assess the likelihood of developing atherosclerosis, in certain chronic diseases (diabetes mellitus, diseases of the kidneys and liver, thyroid gland), as well as as a screening study for the early detection of persons with abnormal lipid profile ...
The doctor gives the patient a referral to the lipid profile
Preparation for research
The lipid profile values can fluctuate not only depending on the sex and age of the subject, but also on the impact on the body of various external and internal factors. To minimize the likelihood of an unreliable result, you must adhere to several rules:
- Blood should be donated strictly in the morning on an empty stomach; in the evening of the previous day, a light dietary dinner is recommended.
- Do not smoke or drink alcohol on the eve of the study.
- Avoid stressful situations and intense physical activity 2-3 days before donating blood.
- Refuse to use all medicines and dietary supplements, except for vital ones.
Methodology
There are several methods for laboratory assessment of the lipid profile. In medical laboratories, analysis can be performed manually or using automatic analyzers. The advantage of the automated measurement system is the minimum risk of erroneous results, the speed of obtaining the analysis, and the high accuracy of the study.
The analysis requires the patient's venous blood serum. Blood is drawn into a vacuum tube using a syringe or vacutainer. To avoid clotting, the blood tube should be inverted several times, then centrifuged to obtain serum. The sample can be stored in the refrigerator for up to 5 days.
Taking blood for lipid profile
Nowadays, blood lipids can be measured from the comfort of your home. To do this, you need to purchase a portable biochemical analyzer that allows you to assess the level of total cholesterol in the blood or several indicators at once in a matter of minutes. For the study, you need a drop of capillary blood, it is applied to the test strip. The test strip is impregnated with a special composition, for each indicator it is different. The results are read automatically after the strip is inserted into the device. The analyzer's small size and battery-powered operation make it easy to use at home and take with you on a trip. Therefore, persons with a predisposition to cardiovascular diseases are advised to have it at home.
Interpretation of results
The most ideal result of the analysis for the patient will be a laboratory conclusion about the absence of deviations from the norm. In this case, a person need not be afraid for the state of his circulatory system - there is practically no risk of atherosclerosis.
Unfortunately, this is not always the case. Sometimes the doctor, after reviewing the laboratory data, makes a conclusion about the presence of hypercholesterolemia. What it is? Hypercholesterolemia - an increase in the concentration of total cholesterol in the blood above normal values, while there is a high risk of developing atherosclerosis and related diseases. This condition may be due to a number of reasons:
- Heredity. Science knows cases of familial hypercholesterolemia (FHC), in such a situation the defective gene responsible for lipid metabolism is inherited. In patients, there is a constantly increased level of TC and LDL, the disease is especially severe in the homozygous form of FHC. In such patients, there is an early onset of coronary artery disease (at the age of 5-10 years), in the absence of proper treatment, the prognosis is poor and in most cases ends in death before reaching 30 years.
- Chronic diseases. Elevated cholesterol levels are observed in diabetes mellitus, hypothyroidism, kidney and liver pathology, due to lipid metabolism disorders due to these diseases.
For patients with diabetes, it is important to constantly monitor cholesterol levels.
- Improper nutrition. Prolonged abuse of fast food, fatty, salty foods leads to obesity, while, as a rule, lipid levels are abnormal.
- Bad habits. Alcoholism and smoking lead to disruptions in the mechanism of fat metabolism, as a result of which the lipid profile increases.
With hypercholesterolemia, you must adhere to a diet that is limited to fat and salt, but in no case should you completely abandon all foods rich in cholesterol. Only mayonnaise, fast food and all products containing trans fats should be excluded from the diet. But eggs, cheese, meat, sour cream must be present on the table, you just need to choose products with a lower percentage of fat. Also in the diet is important the presence of greens, vegetables, cereals, nuts, seafood. The vitamins and minerals they contain perfectly help to stabilize lipid metabolism.
An important condition for the normalization of cholesterol is also the rejection of bad habits. Constant physical activity is also useful for the body.
In the event that a healthy lifestyle in combination with a diet did not lead to a decrease in cholesterol, it is necessary to prescribe an appropriate drug treatment.
Drug treatment for hypercholesterolemia includes prescribing statins
Sometimes specialists are faced with a decrease in cholesterol levels - hypocholesterolemia. Most often, this condition is due to insufficient intake of cholesterol from food. Fat deficiency is especially dangerous for children, in such a situation there will be a lag in physical and mental development, cholesterol is vital for a growing body. In adults, hypocholesteremia leads to a violation of the emotional state due to malfunctions of the nervous system, problems with reproductive function, decreased immunity, etc.
A change in the lipid profile of the blood inevitably affects the work of the whole organism as a whole, therefore it is important to systematically monitor the indicators of fat metabolism for timely treatment and prevention.
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The site provides background information for informational purposes only. Diagnosis and treatment of diseases must be carried out under the supervision of a specialist. All drugs have contraindications. A specialist consultation is required!
What are lipids?
Lipids are one of the groups of organic compounds of great importance for living organisms. According to their chemical structure, all lipids are divided into simple and complex. The molecule of simple lipids is composed of alcohol and bile acids, while complex lipids also contain other atoms or compounds. In general, lipids are of great importance to humans. These substances are found 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 the Greek root meaning "fat", but these definitions still have some differences. Lipids are a broader group of substances, while fats are understood to mean only some types of lipids. Synonymous with "fats" are "triglycerides", which are derived from a 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 found in almost all body tissues. Their molecules are in any living cell, and without these substances life is simply impossible. A lot of different lipids are found in the human body. Each kind or class of these compounds has its own functions. Many biological processes depend on the normal intake and formation of lipids. From the point of view of biochemistry, lipids are involved in the following important processes:
- energy production by the body;
- cell division;
- transmission of nerve impulses;
- the formation of blood components, hormones and other important substances;
- protection and fixation of some internal organs;
- cell division, respiration, etc.
The biological role of lipids in a living cell
Lipid molecules perform a huge number of functions not only on the scale of the whole organism, but also in each living cell separately. In fact, a cell is a structural unit of a living organism. It contains assimilation and synthesis ( education) certain substances. Some of these substances are used to maintain the vital activity of the cell itself, some to divide the cell, 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. When 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 fat. Most of their volume is occupied by a large drop of fat. It is from adipocytes that adipose tissue in the body consists. The largest reserves of adipose tissue are found in the subcutaneous fat, the greater and lesser omentum ( in the abdominal cavity). With prolonged fasting, adipose tissue gradually breaks down, since lipid reserves are used to obtain energy.Also, adipose tissue deposited in the subcutaneous fat provides thermal insulation. Lipid-rich tissues are generally less conductive to heat. This allows the body to maintain a constant body temperature and not so quickly cool or overheat in 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. The lipids that form the cell membrane also help maintain the shape of the cell.Why do lipids-monomers form a double layer ( bilayer)?
Monomers are chemicals ( in this case - molecules), which are capable of connecting to form more complex connections. 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 formed due to the fact that lipid molecules are deployed with hydrophilic parts inside the cell and outside. The hydrophobic parts are practically in contact, since they are located between two layers. Other molecules ( 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 a few connections perform it. For example, lipoproteins, which are made up of lipids and proteins, carry substances in the blood from one organ to another. However, this function is rarely isolated, apart from considering it 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 a significant amount of phospholipids and cholesterol. They neutralize excess pancreatic enzymes and prevent them from damaging intestinal cells. Also, dissolution occurs in bile ( emulsification) exogenous lipids from food. Thus, lipids play a huge role in digestion and aid in the work of other enzymes, although they are not enzymes in themselves.Signal function
Some of the complex lipids have a signaling function in the body. It consists in maintaining various processes. For example, glycolipids in nerve cells are involved in the transmission of nerve impulses from one nerve cell to another. In addition, the signals within the cell itself are of great importance. She needs to "recognize" substances coming from 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. Also lipids are part of prostaglandins. These substances are produced during inflammatory processes and affect some processes in the nervous system ( e.g. perception of pain).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 generate energy.Also, lipids to one degree or another are associated with the metabolism of the following substances:
- Adenosine triphosphoric acid ( ATF). ATP is a kind of unit of energy inside the 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 the building blocks of DNA and are found in the nuclei of living cells. The energy generated by the breakdown of fats is partly used for cell division. During division, new DNA strands are formed from nucleic acids.
- Amino acids. Amino acids are the structural components of proteins. In combination with lipids, they form complex complexes, lipoproteins, which are responsible for the transport of substances in the body.
- Steroids. Steroids are a type of hormone that contains significant amounts of lipids. With poor absorption of lipids from food, the patient may have problems with the endocrine system.
Digestion and absorption of lipids ( metabolism, metabolism)
The digestion and absorption of lipids is the first step in the metabolism of these substances. The main part of lipids enters the body with food. In the oral cavity, food is chopped and mixed with saliva. Further, the lump enters the stomach, where chemical bonds are partially destroyed by the action of hydrochloric acid. Also, some chemical bonds in lipids are destroyed by the enzyme lipase contained in saliva.Lipids are insoluble in water, so in the duodenum they are not immediately digested by enzymes. First, the so-called emulsification of fats occurs. After that, the chemical bonds are cleaved by lipase coming from the pancreas. In principle, for each type of lipid, its own enzyme is now defined, which is responsible for the breakdown and assimilation of this substance. For example, phospholipase breaks down phospholipids, cholesterol esterase - cholesterol compounds, etc. All these enzymes are found in varying amounts in pancreatic juice.
The cleaved lipid fragments are absorbed separately by the cells of the small intestine. In general, the digestion of fats 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 food lump that enters the duodenum, fats are contained in the form of large drops. This prevents them from interacting with enzymes. In the process of emulsification, large fat droplets are "crushed" into smaller droplets. As a result, the area of contact between the fat droplets and the surrounding water-soluble substances increases, and lipid breakdown becomes possible.The process of emulsifying 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 promote their "crushing" into small droplets.
- Bile secreted from the liver accumulates in the gallbladder. Here she concentrates and stands out as needed.
- When fatty foods are consumed, a signal is sent to the smooth muscles of the gallbladder to contract. As a result, a portion of bile is secreted through the bile ducts into the duodenum.
- In the duodenum, the actual emulsification of fats and their interaction with pancreatic enzymes takes place. The contractions in the walls of the small intestine facilitate this process by “mixing” the contents.
Enzymes for the breakdown of lipids
For the digestion of each substance, the body has its own enzymes. Their task is to destroy chemical bonds between molecules ( or between atoms in molecules) so that nutrients can be normally absorbed by the body. Different enzymes are responsible for the breakdown of different lipids. Most of them are found in the juice secreted by the pancreas.The following groups of enzymes are responsible for the breakdown of lipids:
- lipase;
- phospholipases;
- cholesterol esterase, etc.
What vitamins and hormones are involved in lipid regulation?
Most lipids in human blood are relatively constant. It can fluctuate within certain limits. It depends on the biological processes occurring in the body itself, and on a number of external factors. The regulation of blood lipids is a complex biological process that involves many different organs and substances.The following substances play the greatest role in the assimilation and maintenance of a constant lipid level:
- Enzymes. A number of pancreatic enzymes are involved in the breakdown of lipids that enter 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. Normal lipid assimilation is also impossible without these substances.
- Vitamins. Vitamins have a complex strengthening effect on the body and directly or indirectly also affect lipid metabolism. For example, with a lack of vitamin A, the regeneration of cells in the mucous membranes worsens, and the digestion of substances in the intestine also slows down.
- Intracellular enzymes. The cells of the intestinal epithelium 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 have a profound effect on blood lipid levels. That is why some norms have been revised for patients with diabetes mellitus. Thyroid hormones, glucocorticoid hormones, or norepinephrine can stimulate the breakdown of adipose tissue with the release of energy.
Biosynthesis ( education) and hydrolysis ( decay) lipids in the body ( anabolism and catabolism)
Metabolism is a set of metabolic processes in the body. All metabolic processes can be divided into catabolic and anabolic. The catabolic processes include the splitting and disintegration of substances. For lipids, this is characterized by their hydrolysis ( decay 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 the 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 break down, and new substances are synthesized from them. For example, the formation of compounds of cholesterol and phospholipids occurs here, which are then excreted in the bile and contribute to normal digestion.
- Cells of other organs. Part of the lipids passes through the blood to other organs and tissues. Depending on the type of cells, lipids are converted into a certain type of compound. All cells, one way or another, synthesize lipids to form a cell wall ( lipid bilayer). In the adrenal glands and gonads, steroid hormones are synthesized from part of the lipids.
Resynthesis of lipids in the liver and other organs
Resynthesis is the process of formation of certain substances from simpler ones that were assimilated earlier. In the body, this process takes place in the internal environment of some cells. Resynthesis is necessary in order for tissues and organs to receive all the necessary types of lipids, and not just those that were 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, the fatty acids supplied with food are converted into transport forms, which are sent with the blood to the liver and other organs. A part of the resynthesized lipids will be delivered to the tissues, from the other part, the substances necessary for vital activity are 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 constituent of nerve cells, not only in the brain, but throughout the entire 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 due to the myelin sheath of nerve cells. Myelin, which prevents the chaotic propagation of impulses, is approximately 75% lipids. As in cell membranes, here they form a double layer ( bilayer), which is wrapped around the nerve cell several times.The myelin sheath in the nervous system contains the following lipids:
- phospholipids;
- cholesterol;
- galactolipids;
- glycolipids.
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 the cells of adipose tissue. Steroid hormones are involved 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 found in the following vital hormones:
- corticosteroids ( cortisol, aldosterone, hydrocortisone, etc.);
- male sex hormones - androgens ( androstenedione, dihydrotestosterone, etc.);
- female sex hormones - estrogens ( estriol, estradiol, etc.).
The role of lipids in skin and hair
Lipids are of great importance for the health of the skin and its appendages ( hair and nails). The skin contains the so-called sebaceous glands, which secrete to the surface a certain amount of secretion rich in fats. This substance has 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) the sebaceous glands moisturize the skin;
- thanks to fats, the firmness, elasticity and smoothness of the skin are maintained;
- a small amount of lipids on the surface of the hair gives it a healthy shine;
- the lipid layer on the skin surface protects it from the aggressive effects of external factors ( cold, sun rays, microbes on the surface of the skin, etc.).
Lipid classification
In biology and chemistry, there are quite a few different classifications of lipids. The main one is chemical classification, according 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 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 using 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 ways. For example, when using various cosmetics or drugs, the body can also receive some 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 will be formed, which the body needs. These lipids, synthesized by their 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 of the components of complex lipids cannot be synthesized by the body on its own, which is reflected in the course of certain biological processes.
Fatty acid
Fatty acids is a class of organic compounds that are the structural part of lipids. Depending on what kind of fatty acids are part of the lipid, the properties of this substance may change. For example, triglycerides, the most important energy source for the human body, are derived from glycerol alcohol and several fatty acids.Naturally, fatty acids are found in a wide variety of substances, from petroleum to vegetable oils. They enter the human body mainly with 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.).
Saturated and unsaturated fatty acids
All fatty acids are divided into saturated and unsaturated ones by their chemical structure. Saturated acids are less beneficial for the body, and some of them are even harmful. This is due to the fact that there are no double bonds in the molecule of these substances. These are chemically stable compounds, and they are less well absorbed by the body. Currently, the connection of some saturated fatty acids with 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 thus more active. It is believed that eating them can lower cholesterol levels and prevent the development of atherosclerosis. The largest 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 polyunsaturated fatty acids do not enter the body with 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, and more.
Phospholipids
Phospholipids are complex lipids containing a phosphoric acid residue. These substances, along with cholesterol, are the main component of cell membranes. Also, these substances are involved 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 in the bile is more, cholesterol or phospholipids, you can determine the risk of developing gallstone disease.Glycerin and triglycerides
In terms of 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 the supply of 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 work the muscles ( skeletal muscles, heart 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 due to differences in classifications. This is one of the lipoprotein fractions in the body, which plays an important role in the development of some pathologies. First of all, we are talking about atherosclerosis. Beta-lipoproteins transport cholesterol from one cell to another, but due to the structural characteristics of the molecules, this cholesterol often "gets stuck" in the walls of blood vessels, forming atherosclerotic plaques and interfering with normal blood flow. Before use, you must consult a specialist. Lipids - these are fat-like organic compounds, insoluble in water, but readily soluble in non-polar solvents (ether, gasoline, benzene, chloroform, etc.). Lipids belong to the simplest biological molecules.Chemically, most lipids are esters of higher carboxylic acids and a number of alcohols. The best known among them are fats. Each fat molecule is formed by a molecule of a triatomic alcohol of glycerol and attached to it ether bonds of three molecules of higher carboxylic acids. According to the accepted nomenclature, fats are called triacylglcherols.
The carbon atoms in the molecules of higher carboxylic acids can be connected to each other by both single and double bonds. Of the limiting (saturated) higher carboxylic acids, palmitic, stearic, arachidic acids are most often included in the composition of fats; from unsaturated (unsaturated) - oleic and linoleic.
The degree of unsaturation and the chain length of higher carboxylic acids (i.e., the number of carbon atoms) determine the physical properties of a particular fat.
Fats with short and unsaturated acid chains have a low melting point. At room temperature, these are liquids (oils) or greasy substances (fats). Conversely, fats with long and saturated chains of higher carboxylic acids become solid at room temperature. That is why, during hydrogenation (saturation of acid chains with hydrogen atoms along double bonds), liquid peanut oil, for example, becomes buttery-like, and sunflower oil turns into solid margarine. Compared to inhabitants of southern latitudes, animals living in cold climates (for example, fish from the Arctic seas) usually contain more unsaturated triacylglycerols. For this reason, their body remains flexible even at low temperatures.
In phospholipids, one of the extreme chains of the higher carboxylic acids of triacylglycerol is replaced by a group containing phosphate. Phospholipids have polar heads and non-polar tails. The groups forming the polar head are hydrophilic, and the non-polar tail groups are hydrophobic. The dual nature of these lipids determines their key role in the organization of biological membranes.
Another group of lipids are steroids (sterols). These substances are based on cholesterol alcohol. Sterols are poorly soluble in water and do not contain higher carboxylic acids. These include bile acids, cholesterol, sex hormones, vitamin D, etc.
Lipids also include terpenes (plant growth substances - gibberellins; carotenoids - photosynthetic pigments; essential oils of plants, as well as waxes).
Lipids can form complexes with other biological molecules - proteins and sugars.
The functions of lipids are as follows:
Structural. Phospholipids, together with proteins, form biological membranes. The membranes also contain sterols.
Energy. When fat is oxidized, a large amount of energy is released, which goes into the formation of ATP. A significant part of the body's energy reserves is stored in the form of lipids, which are consumed when there is a lack of nutrients. Hibernating animals and plants accumulate fats and oils and use them to maintain vital processes. The high content of lipids in plant seeds ensures the development of the embryo and seedling before their transition to independent feeding. The seeds of many plants (coconut palm, castor oil plant, sunflower, soybean, rapeseed, etc.) are used as raw materials for industrial production of vegetable oil.
Protective and heat-insulating. Accumulating in the subcutaneous tissue and around some organs (kidneys, intestines), the fat layer protects the animal body and its individual organs from mechanical damage. In addition, due to its low thermal conductivity, the layer of subcutaneous fat helps to retain heat, which allows, for example, many animals to live in cold climates. In addition, it plays another role in whales - it contributes to buoyancy.
Lubricating and water repellent. The wax covers the skin, wool, feathers, makes them more elastic and protects them from moisture. Leaves and fruits of many plants have a waxy coating.
Regulatory. Many hormones are derivatives of cholesterol, such as sex hormones (testosterone in men and progesterone in women) and corticosteroids (aldosterone). Cholesterol derivatives, vitamin D play a key role in calcium and phosphorus metabolism. Bile acids are involved in the processes of digestion (emulsification of fats) and the absorption of higher carboxylic acids.
Lipids are also the source of metabolic water formation. Oxidation of 100 g of fat gives about 105 g of water. This water is very important for some desert inhabitants, in particular for camels, which can go without water for 10-12 days: the fat stored in the hump is used for this very purpose. Bears, marmots and other hibernating animals receive the water necessary for life as a result of fat oxidation.
In the myelin sheaths of the axons of nerve cells, lipids are insulators during the conduction of nerve impulses.
The wax is used by bees to build honeycombs.
One of the biggest myths of modern mankind is the harmfulness of fats. Fat has become enemy number one. People spend dollars, rubles, euros and so on to buy fat-free cookies, fat-free cola, pills that can inhibit the absorption of fat, pills that dissolve fat. People are on all kinds of fat-free diets.
But ... In countries that are prosperous in all respects, the number of obese people is steadily growing. A growing number of people suffering from cardiovascular diseases and diabetes mellitus, that is, diseases that are largely associated with overweight. The war on fats continues ...
So what's wrong?
Fact 1: fats are good for you
The first and main mistake is to assume that all fats are the same, rejecting all fats is a blessing. However, the education of the population is quite high, now many people know that unsaturated fats (mainly vegetable) are useful. And saturated (mainly animals) are harmful.
Let's figure it out.
Saturated fats are structural components of cell membranes and are involved in the biochemistry of the body. Therefore, a complete rejection of them will lead to irreversible changes in health. Another thing is that their consumption should correspond to age indicators. Children and adolescents need them in sufficient quantities, their consumption can be reduced with age.
Unsaturated fats - reduce the level of "bad" cholesterol, are necessary for the assimilation of some vitamins (fat-soluble), are involved in metabolism. That is, these fats are also necessary for the body.
A little observation: saturated fats are solid, unsaturated fats are liquid.
According to physiological indicators for the average person, the ratio of saturated - unsaturated fats should be 1/3: 2/3. Eating healthy fats is essential!
Trans fats are definitely harmful. They are also found in nature (for example, in natural milk), but for the most part they are formed from other (vegetable) fats, by hydrogenation (a method of processing fats to give them a solid form).
Fact 2: body fat is not the result of eating fat
What?! Of course, if you simply increase your fat intake without reducing other foods, you will gain weight. The basis for maintaining a healthy weight is balance. You should be spending as many calories as you consume.
But diets with a sharp calorie restriction can lead to a sharp increase in weight after cancellation. Why? The body received the installation: hunger. Hence, it is necessary to accumulate fats in reserve. Therefore, all food is processed and goes to the "depot" - fatty deposits. In this case, you can fall into hungry faints. Processed carbohydrates are stored in fat stores.
Studies show that if a person is on a low-calorie, fat-free diet, then with great difficulty shed a few pounds will return, even if you continue to "sit" on this diet.
In addition, people who eat a small amount of fat are prone to obesity.
And observation of patients in the United States revealed a picture that a decrease in the amount of fat from 40% (which is considered the norm) to 33% in the diet is accompanied by an increase in overweight people.
Remember that unsaturated fats are involved in the metabolism. The ratio of protein: fat: carbohydrates for an adult should be approximately 14%: 33%: 53%.
Output: an increase in unsaturated fats in food with a constant calorie content will not lead to weight gain, but will contribute to improving health through metabolism.
Lipids- Substances very heterogeneous in their chemical structure, characterized by different solubility in organic solvents and, as a rule, insoluble in water. They play an important role in life processes. As one of the main components of biological membranes, lipids affect their permeability, participate in the transmission of nerve impulses, and the creation of intercellular contacts.
Other functions of lipids are the formation of an energy reserve, the creation of protective water-repellent and thermal insulating covers in animals and plants, the protection of organs and tissues from mechanical stress.
CLASSIFICATION OF LIPIDS
Depending on the chemical composition, lipids are divided into several classes.
- Simple lipids include substances whose molecules consist only of residues of fatty acids (or aldehydes) and alcohols. These include
- fats (triglycerides and other neutral glycerides)
- waxes
- Complex lipids
- derivatives of phosphoric acid (phospholipids)
- lipids containing sugar residues (glycolipids)
- sterols
- sterides
In this section, lipid chemistry will be considered only to the extent that is necessary for understanding lipid metabolism.
If animal or plant tissue is treated with one or more (more often sequentially) organic solvents, for example chloroform, benzene or petroleum ether, then some of the material goes into solution. The components of this soluble fraction (extract) are called lipids. The lipid fraction contains substances of various types, most of which are shown in the diagram. Note that due to the heterogeneity of the components included in the lipid fraction, the term "lipid fraction" cannot be regarded as a structural characteristic; it is only a working laboratory name for the fraction obtained from the extraction of biological material with low-polarity solvents. Nevertheless, most lipids share some common structural features that determine their important biological properties and similar solubility.
Fatty acid
Fatty acids - aliphatic carboxylic acids - in the body can be in a free state (trace amounts in cells and tissues) or serve as building blocks for most classes of lipids. Over 70 different fatty acids have been isolated from the cells and tissues of living organisms.
Fatty acids found in natural lipids contain an even number of carbon atoms and have a predominantly unbranched carbon chain. Below are the formulas for the most commonly found natural fatty acids.
Natural fatty acids, although somewhat conditionally, can be divided into three groups:
- saturated fatty acids [show]
- monounsaturated fatty acids [show]
Monounsaturated (with one double bond) fatty acids:
- polyunsaturated fatty acids [show]
Polyunsaturated (with two or more double bonds) fatty acids:
In addition to these main three groups, there is also a group of so-called unusual natural fatty acids [show] .
The fatty acids that make up the lipids of animals and higher plants have many properties in common. As already noted, almost all natural fatty acids contain an even number of carbon atoms, most often 16 or 18. Unsaturated fatty acids of animals and humans, which are involved in the construction of lipids, usually contain a double bond between the 9th and 10th carbon, additional double bonds, such as usually occur between the 10th carbon and the methyl end of the chain. The count comes from the carboxyl group: the C-atom closest to the COOH group is designated as α, the adjacent one is β, and the terminal carbon atom in the hydrocarbon radical is ω.
The peculiarity of double bonds of natural unsaturated fatty acids lies in the fact that they are always separated by two simple bonds, that is, there is always at least one methylene group between them (-CH = CH-CH 2 -CH = CH-). Such double bonds are referred to as "isolated". Naturally occurring unsaturated fatty acids have a cis configuration and trans configurations are extremely rare. It is believed that in unsaturated fatty acids with several double bonds, the cis configuration gives the hydrocarbon chain a curved and shortened appearance, which makes a biological sense (especially when you consider that many lipids are part of membranes). In microbial cells, unsaturated fatty acids usually contain one double bond.
Long chain fatty acids are practically insoluble in water. Their sodium and potassium salts (soaps) form micelles in water. In the latter, negatively charged carboxyl groups of fatty acids face the aqueous phase, and non-polar hydrocarbon chains are hidden inside the micellar structure. Such micelles have a total negative charge and remain suspended in solution due to mutual repulsion (Fig. 95).
Neutral fats (or glycerides)
Neutral fats are esters of glycerol and fatty acids. If all three hydroxyl groups of glycerol are esterified with fatty acids, then such a compound is called triglyceride (triacylglycerol), if two - diglyceride (diacylglycerol) and, finally, if one group is esterified - monoglyceride (monoacylglycerol).
Neutral fats are found in the body either in the form of protoplasmic fat, which is a structural component of cells, or in the form of reserve, reserve fat. The role of these two forms of fat in the body is not the same. Protoplasmic fat has a constant chemical composition and is contained in tissues in a certain amount, which does not change even with morbid obesity, while the amount of reserve fat is subject to large fluctuations.
The bulk of natural neutral fats are triglycerides. The fatty acids in triglycerides can be saturated or unsaturated. Palmitic, stearic and oleic acids are more common among fatty acids. If all three acid radicals belong to the same fatty acid, then such triglycerides are called simple (for example, tripalmitin, tristearin, triolein, etc.), but if they are different fatty acids, then they are called mixed. Mixed triglycerides are named from their constituent fatty acids; the numbers 1, 2 and 3 indicate the bond of the fatty acid residue with the corresponding alcohol group in the glycerol molecule (for example, 1-oleo-2-palmitostearin).
Fatty acids that make up triglycerides practically determine their physicochemical properties. Thus, the melting point of triglycerides increases with an increase in the number and length of saturated fatty acid residues. In contrast, the higher the content of unsaturated fatty acids or short-chain acids, the lower the melting point. Animal fats (lard) usually contain a significant amount of saturated fatty acids (palmitic, stearic, etc.), due to which they are solid at room temperature. Fats, which contain many mono- and polyunsaturated acids, are liquid at ordinary temperatures and are called oils. So, in hemp oil, 95% of all fatty acids are oleic, linoleic and linolenic acids, and only 5% are stearic and palmitic acids. Note that human fat melting at 15 ° C (it is liquid at body temperature) contains 70% oleic acid.
Glycerides are able to enter into all chemical reactions inherent in esters. Of greatest importance is the saponification reaction, as a result of which glycerol and fatty acids are formed from triglycerides. Saponification of fat can occur both by enzymatic hydrolysis and by the action of acids or alkalis.
Alkaline cleavage of fat by the action of caustic soda or caustic potash is carried out in the industrial production of soap. Recall that soap is sodium or potassium salts of higher fatty acids.
The following indicators are often used to characterize natural fats:
- iodine number - the number of grams of iodine, which, under certain conditions, binds 100 g of fat; this number characterizes the degree of unsaturation of fatty acids present in fats, the iodine number of beef fat 32-47, lamb 35-46, pork 46-66;
- acid number - the number of milligrams of caustic potassium required to neutralize 1 g of fat. This number indicates the amount of free fatty acids present in the fat;
- saponification number - the number of milligrams of caustic potassium consumed to neutralize all fatty acids (both included in triglycerides and free) contained in 1 g of fat. This number depends on the relative molecular weight of the fatty acids that make up the fat. The saponification number for the main animal fats (beef, lamb, pork) is practically the same.
Waxes are esters of higher fatty acids and higher monohydric or dihydric alcohols with the number of carbon atoms from 20 to 70. Their general formulas are shown in the diagram, where R, R "and R" are possible radicals.
Waxes can be part of the fat that covers the skin, wool, feathers. In plants, 80% of all lipids that form a film on the surface of leaves and trunks are waxes. It is also known that waxes are normal metabolites of some microorganisms.
Natural waxes (for example, beeswax, spermaceti, lanolin) usually contain, in addition to the aforementioned esters, a certain amount of free higher fatty acids, alcohols and hydrocarbons with 21-35 carbon atoms.
Phospholipids
This class of complex lipids includes glycerophospholipids and sphingolipids.
Glycerophospholipids are derivatives of phosphatidic acid: they contain glycerol, fatty acids, phosphoric acid, and usually nitrogen-containing compounds. The general formula of glycerophospholipids is shown in the diagram, where R 1 and R 2 are radicals of higher fatty acids, and R 3 is a radical of a nitrogenous compound.
It is characteristic of all glycerophospholipids that one part of their molecule (radicals R 1 and R 2) exhibits pronounced hydrophobicity, while the other part is hydrophilic due to the negative charge of the phosphoric acid residue and the positive charge of the radical R 3.
Of all lipids, glycerophospholipids have the most pronounced polar properties. When glycerophospholipids are placed in water, only a small part of them passes into a true solution, while the bulk of the "dissolved" lipid is in aqueous systems in the form of micelles. There are several groups (subclasses) of glycerophospholipids.
- [show]
.
- Phosphatidylserines [show]
.
In the phosphatidylserine molecule, the nitrogenous compound is the serine amino acid residue.
Phosphatidylserines are much less widespread than phosphatidylcholines and phosphatidylethanolamines, and their importance is determined mainly by the fact that they are involved in the synthesis of phosphatidylethanolamines.
- Plasmalogens (acetal phosphatides) [show]
.
They differ from the glycerophospholipids discussed above in that instead of one higher fatty acid residue, they contain a fatty acid aldehyde residue, which is linked to the hydroxyl group of glycerol by an unsaturated ester bond:
Thus, during hydrolysis, plasmalogen decomposes into glycerol, higher fatty acid aldehyde, fatty acid, phosphoric acid, choline, or ethanolamine.
[show]
.
Unlike triglycerides in the phosphatidylcholine molecule, one of the three hydroxyl groups of glycerol is associated not with fatty acid, but with phosphoric acid. In addition, phosphoric acid, in turn, is linked with an ether bond with a nitrogenous base [HO-CH 2 -CH 2 -N + = (CH 3) 3] - choline. Thus, glycerol, higher fatty acids, phosphoric acid and choline are combined in the phosphatidylcholine molecule.
[show] .
The main difference between phosphatidylcholines and phosphatidylethanolamines is that the latter include the nitrogenous base ethanolamine (HO-CH 2 -CH 2 -NH 3 +) instead of choline.
Of the glycerophospholipids in the body of animals and higher plants, phosphatidylcholines and phosphatidylethanolamines are found in the greatest amount. These two groups of glycerophospholipids are metabolically linked to each other and are the main lipid components of cell membranes.
The R 3 -radical in this group of glycerophospholipids is a six-carbon sugar alcohol - inositol:
Phosphatidylinositols are quite widespread in nature. They are found in animals, plants and microbes. In the animal body, they are found in the brain, liver and lungs.
[show] . 
It should be noted that free phosphatidic acid is found in nature, although in comparison with other glycerophospholipids in relatively small amounts.
Cardiolilin belongs to glycerophospholipids, more precisely to polyglycerol phosphates. The backbone of the cardiolipin molecule includes three glycerol residues connected to each other by two phosphodiester bridges through positions 1 and 3; the hydroxyl groups of the two outer glycerol residues are esterified with fatty acids. Cardiolipin is part of the mitochondrial membranes. Table 29 summarizes the data on the structure of the main glycerophospholipids.
Among the fatty acids that make up glycerophospholipids, both saturated and unsaturated fatty acids (more often stearic, palmitic, oleic and linoleic) are found.
It was also found that most phosphatidylcholines and phosphatidylethanolamines contain one saturated higher fatty acid esterified at position 1 (at the 1st carbon atom of glycerol), and one unsaturated higher fatty acid esterified at position 2. Hydrolysis of phosphatidylcholines and phosphatidylethanolamines with the participation of special enzymes , for example, in the venom of the cobra, which belong to phospholipases A 2, leads to the elimination of unsaturated fatty acids and the formation of lysophosphatidylcholines or lysophosphatidylethanolamines with a strong hemolytic effect.
Sphingolipids
Glycolipids
Complex lipids containing carbohydrate groups in the molecule (more often a D-galactose residue). Glycolipids play an essential role in the functioning of biological membranes. They are found predominantly in brain tissue, but they are also found in blood cells and other tissues. There are three main groups of glycolipids:
- cerebrosides
- sulfatides
- gangliosides
Cerebrosides contain neither phosphoric acid nor choline. They include hexose (usually D-galactose), which is linked by an ether bond to the hydroxyl group of the amino alcohol sphingosine. In addition, a fatty acid is a part of cerebroside. Among these fatty acids, the most common are lignoceric, nervous and cerebronic acids, i.e. fatty acids having 24 carbon atoms. The structure of cerebrosides can be represented by the diagram. Cerebrosides can also be classified as sphingolipids, since they contain the alcohol sphingosine.
The most studied representatives of cerebrosides are the nerve containing neurotic acid, the cerebron, which contains cerebronic acid, and kerazine, which contains lignocyric acid. The content of cerebrosides is especially high in the membranes of nerve cells (in the myelin sheath).
Sulfatides differ from cerebrosides in that they contain a sulfuric acid residue in the molecule. In other words, the sulfatide is a cerebroside sulfate in which the sulfate is esterified at the third carbon atom of the hexose. In the mammalian brain, sulfatides, like cerebrosides, are found in the white matter. However, their content in the brain is much lower than that of cerebrosides.
During the hydrolysis of gangliosides, one can find higher fatty acid, sphingosine alcohol, D-glucose and D-galactose, as well as derivatives of amino sugars: N-acetylglucosamine and N-acetylneuraminic acid. The latter is synthesized in the body from glucosamine.
Structurally, gangliosides are largely similar to cerebrosides, with the only difference that instead of one galactose residue they contain a complex oligosaccharide. One of the simplest gangliosides is hematoside, isolated from the stroma of erythrocytes (scheme)
Unlike cerebrosides and sulfatides, gangliosides are found mainly in the gray matter of the brain and are concentrated in the plasma membranes of nerve and glial cells.
All the lipids considered above are usually called saponifiable, since soaps are formed during their hydrolysis. However, there are lipids that are not hydrolyzed to release fatty acids. These lipids include steroids.
Steroids are naturally occurring compounds. They are derivatives of the core containing three fused cyclohexane and one cyclopentane ring. Steroids include numerous substances of a hormonal nature, as well as cholesterol, bile acids and other compounds.
In the human body, sterols occupy the first place among steroids. The most important representative of sterols is cholesterol:
It contains an alcoholic hydroxyl group at C 3 and a branched aliphatic chain of eight carbon atoms at C 17. The hydroxyl group at C 3 can be esterified with a higher fatty acid; in this case, cholesterol esters (cholesterides) are formed:
Cholesterol plays the role of a key intermediate in the synthesis of many other compounds. Plasma membranes of many animal cells are rich in cholesterol; in a significantly smaller amount, it is contained in the membranes of mitochondria and in the endoplasmic reticulum. Note that there is no cholesterol in plants. Plants have other sterols known collectively as phytosterols.
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