Questions and tasks. Pancreatic hormone regulating carbohydrate metabolism What hormones are involved in the regulation of carbohydrate metabolism
Scientists point out that carbohydrate metabolism important for the body, as it affects the work of different systems. The main task of such a process is to participate in the production of energy that a person needs to carry out his life.
Carbohydrates belong to organic elements that can enrich the body with energy. But their role is not only that. All processes that occur in the body are important and interconnected. Therefore, carbohydrates in the body can be either separate components or be associated with proteins or fats.
Violation of the production of carbohydrates in the body will cause a failure in all systems. This is confirmed by biochemistry. The body will not be able to produce enough hormones involved in metabolism, as well as other biochemical reactions.
About the role of carbohydrates in the body, what hormonal processes they regulate, as well as metabolism will be discussed in this article below.
When eating is usually consumed by a person a large number of carbohydrates. They can provide the body with the necessary energy, and also provide about 50% of the values \u200b\u200bthat are important for the functioning of systems in the body. Therefore, they must be consumed daily in large quantities. As the load on the body increases, it will require more carbohydrates, which help produce hormones.
But these elements act not only as a replenisher of energy costs. Together with fats and proteins, they can participate in the process of cell regeneration and growth. They are able to produce acids, providing and controlling the right amount of glucose in the body.
It is worth noting that almost all foods contain carbohydrates. They are also present in all living organisms, taking part in the growth and construction of the structure.
The main functions of carbohydrates are:
- Making the brain work.
- Energy supply.
- Controlling the amount of lipids and proteins.
- production of certain types of molecules.
- Improvement of the digestive tract.
- Removal of toxins from the body.
- Activation of food digestion processes.
Biochemistry confirms that impaired carbohydrate metabolism can become not only the cause of the pathologies listed above. These elements not only help the body replenish the spent energy, but can also participate in metabolic processes and generation in cells.
Kinds
Modern biochemistry distinguishes several types of carbohydrates, which may differ in their structure and components. They are usually divided into two groups:
- Complex.
- Simple.
Also, according to their chemical characteristics, they are also divided into:
- Monosaccharides.
- Polysaccharides.
- Oligosaccharides.
A feature of monosaccharides is that they can have a sugar molecule in their structure. When split, such elements can enter the bloodstream and increase the level of sugar in it.
The basis of the polysaccharide is a large number of monosaccharides. Their synthesis and processing in the gastrointestinal tract after a meal takes a long time. But with the help of them, a person will have a stable indicator of blood sugar levels.
Although the main process of carbohydrate breakdown occurs in the gastrointestinal tract, the process itself begins in the mouth. Saliva helps this, and therefore it is recommended to chew food thoroughly.
carbohydrate metabolism
Of course, as experts define it, the main role of carbohydrates is to provide the body with energy. Glucose, which is produced in the body with the participation of carbohydrates, is the main source of energy.
If all human systems work smoothly and correctly, then under stress on the body, an increase in glucose consumption occurs, which makes it possible for the brain and organs to provide psychological and physical processes.
Carbohydrate metabolism is a set of processes that guarantees the processing of carbohydrates themselves into energy. Synthesis begins in the mouth, where the substance can be broken down by enzymes.
But the main process is carried out in the gastrointestinal tract, where a polysaccharide and a monosaccharide are produced, which are then carried by the bloodstream to the cells. At the same time, most of the produced particles remain and accumulate in the liver.
The blood carries glucose around the body all the time. It primarily delivers such a substance to those organs that need it most. Therefore, the speed of glucose transportation depends on the activity of processes in the body.
We must remember that all processes in the body are interconnected. Therefore, when carbohydrates, proteins or fats are exchanged, intermediate substances can also be produced that also take part in metabolism, although they are not so important for it.
With the help of such substances, the body is able to produce a large amount of energy from the food received. It is about 60%.
Lack or excess of carbohydrates
For the regulatory process, these indicators are important. If there are few carbohydrates in the body, this can lead to liver degeneration. Muscles can also be affected. Ketones will begin to accumulate in the blood. At high concentrations, intoxication of the body occurs and the brain is affected.
A large amount of carbohydrates also does not benefit a person. At the initial stage, an increase in carbohydrates can cause an increase in blood sugar, which will negatively affect the work of the pancreas. This leads to the appearance of diabetes and other pathologies.
If the body cannot process all the carbohydrates that it receives with food, then this will cause fat to begin to be deposited in the body. This will lead to obesity, which can negatively affect the body.
Carb imbalance
The balance of these elements in the body can be disturbed for various reasons. It can also lead to the manifestation of pathologies. The main reasons for the violation are:
- Violations of the genetic plan in the central nervous system and endocrine system.
- Disturbances in the development of the fetus in the womb.
- Irrational and improper nutrition.
- The use of sweets in large quantities.
- Drinking alcohol in large quantities.
- Disruptions in the hormonal system.
- Passive lifestyle.
When the process of carbohydrate metabolism is disrupted, a person has problems. He begins to feel bad and experience negative symptoms. This is usually due to the fact that a large or small amount of sugar appears in the blood. It can also cause malfunctions in the work of the WSS.
Possible manifestation of such pathologies:
- Hypoglycemia. It dramatically reduces the amount of sugar in the body. A person may experience blurred vision or dizziness. Also, a person will become nervous, he will have an unclear mind, his skin will turn pale and coordination will be disturbed. When the pathology manifests itself for a long time, it can lead to coma. You can correct the situation by consuming sweets in large quantities.
- Diabetes. When carbohydrate metabolism is disturbed, a person almost always develops diabetes. The main reason is that the amount of insulin in the body decreases and the cells no longer interact properly. The organs also cease to receive the required energy and cannot perform their functions. With such a pathology, a person will have a constant feeling of fatigue, he will lose weight and will not be able to fully have sex. Vision may also deteriorate, wounds will begin to heal more slowly, numbness of the limbs will be felt and other negative symptoms will appear.
Exchange features
Hormones secreted by the thyroid gland can also participate in the normalization and conduct of the metabolic process. They accelerate the formation of glucose and enable cells to absorb it faster.
This exchange is especially important for pregnant women. During this process, the fetus receives the right amount of glucose, which ensures its proper development. The intensity of the metabolic process can also affect the appearance of hypoxia.
It was also noted by doctors that if the body begins to quickly gain weight, then this indicates that it cannot tolerate certain foods that contain a lot of carbohydrates in their composition. This will be especially noticeable in children.
Therefore, when the first negative symptoms appear, which are described above, it is important to immediately visit the clinic and conduct an examination there. This will enable the doctor to start treatment on time if the pathology is detected.
Hormonal regulation and pathologies of carbohydrate metabolism
An excess of glucose in the blood, usually occurring after a meal, stimulates the synthesis of the pancreatic hormone. insulin a, which involves the formation of osmotically inert glycogen in the liver and muscles. Glycogen is a polymeric glucose, similar to starch in plants. Glycogen, in turn, is broken down to glucose under the influence of the hormone glucagon, the secretion of which by the cells of the pancreas begins very quickly when blood glucose levels decrease. If glycogen reserves are exhausted, then complex biochemical systems for the formation of glucose from amino acids are stimulated, and each of the amino acids requires an individual cycle of reactions. Normally, this process occurs constantly, due to the self-renewal of proteins. With a balanced diet, the amino acids of food proteins provide about 10% of the energy needs of the body. Syndromes that lead to impaired blood glucose balance, type 1 diabetes and type 2 diabetes, are the most common chronic diseases in economically developed countries. According to the World Health Organization (WHO), 171 million people were diagnosed with diabetes in 2000, with the United States having the highest incidence of diabetes of any country in the world, at 17.7 million cases. In the Russian Federation, diabetes has been diagnosed in 4.5 million people. Among Asian countries, India (31.7 million diabetics) significantly outpaced China (20.7 million). On the entire African continent, according to WHO, diabetes was detected in 7 million people.
Diabetes-1, which currently accounts for about 8% of carbohydrate metabolic diseases, is a genetic anomaly that manifests itself already in childhood. In this case, the cells of the pancreas that produce insulin are destroyed, and the body loses the ability to regulate blood glucose levels and convert excess glucose into glycogen. The absence of a glycogen reserve of glucose in the liver makes the concentration of glucose in the blood very unstable, and most diabetic patients died in the past, not
This text is an introductory piece. From the book Propaedeutics of childhood diseases author O. V. Osipova From the book Propaedeutics of childhood diseases: lecture notes author O. V. Osipova author Mikhail Borisovich Ingerleib From the book Analyzes. Complete reference author Mikhail Borisovich Ingerleib From the book Analyzes. Complete reference author Mikhail Borisovich Ingerleib From the book Analyzes. Complete reference author Mikhail Borisovich Ingerleib From the book What the tests say. Secrets of medical indicators - for patients author Evgeny Alexandrovich Grin author Yulia Sergeevna Popova From the book How to stop snoring and let others sleep author Yulia Sergeevna Popova author Mikhail Borisovich Ingerleib From the book A complete guide to analyzes and research in medicine author Mikhail Borisovich Ingerleib From the book A complete guide to analyzes and research in medicine author Mikhail Borisovich Ingerleib From the book A complete guide to analyzes and research in medicine author Mikhail Borisovich Ingerleib From the book Diabetes Mellitus. New understanding author Mark Yakovlevich Zholondz From the book Diabetes. Prevention, diagnosis and treatment by traditional and non-traditional methods author Violetta Romanovna Khamidova From the book Learning to understand your analyzes author Elena V. PoghosyanMINISTRY OF EDUCATION OF THE REPUBLIC OF BELARUS
BELARUSIAN STATE ACADEMY OF PHYSICAL CULTURE
DEPARTMENT: "BIOCHEMISTRY"
TOPIC: "HORMONAL REGULATION OF CARBOHYDRATE METABOLISM DURING MUSCLE ACTIVITY"
PERFORMED:
KOVALEVICH
EKATERINA VLADIMIROVNA
1st YEAR STUDENT GROUP No. 112
FACULTY SI and E
MINSK 2002
The concept of hormones, their biological role.
ENDOCRINE SYSTEM- a system of glands that produce hormones and secrete them directly into the blood. These glands, called endocrine or endocrine glands, do not have excretory ducts; they are located in different parts of the body, but are functionally closely interconnected. The figure shows the location of the main endocrine glands in the human body. The pineal gland (pineal gland), which is missing in the figure, has not been studied enough, but at present it is attributed to the endocrine system. This gland is a small formation in the midbrain, and in mammals it plays the role of a neuroendocrine transducer, in which nerve impulses coming from the eyes through the brain are converted into a hormonal signal, causing the secretion of the hormone melatonin. Melatonin affects biological rhythms, including daily fluctuations in physiological functions and seasonal sexual cycles. In lower vertebrates, the pineal gland can directly perceive light (the "third eye").
HORMONES, organic compounds produced by certain cells and designed to control body functions, their regulation and coordination. Higher animals have two regulatory systems by which the body adapts to constant internal and external changes. One is the nervous system, which rapidly transmits signals (in the form of impulses) through a network of nerves and nerve cells; the other is endocrine, which carries out chemical regulation with the help of hormones that are carried by the blood and have an effect on tissues and organs distant from the place of their release. The chemical communication system interacts with the nervous system; Thus, some hormones function as mediators (intermediaries) between the nervous system and organs that respond to exposure. Thus, the distinction between neural and chemical coordination is not absolute.
All mammals, including humans, have hormones; they are also found in other living organisms. The physiological action of hormones is aimed at:
1) providing humoral, i.e. carried out through the blood, the regulation of biological processes;
2) maintaining the integrity and constancy of the internal environment, harmonious interaction between the cellular components of the body;
3) regulation of growth, maturation and reproduction processes.
The pituitary gland is the main gland of internal secretion, on the activity of which the activity of other glands depends. The pituitary gland is located in the cranium under the brain, therefore it is also called the lower cerebral appendage. And by location, and by structure, and by origin, the pituitary gland is connected with the nervous system, which exerts influence on it, enhancing or inhibiting the production of its hormones.
Despite the small size and weight of only about half a gram, the pituitary gland is essentially two glands combined in one organ (the anterior lobe is one gland, and the posterior and intermediate lobe is the second gland).
The pituitary gland consists of three lobes - the anterior, consisting of glandular tissue cells, the posterior, consisting of nervous tissue cells, and the intermediate, closely associated with the posterior lobe. Each of the lobes of the pituitary gland produces its own hormones.
Hormones regulate the activity of all body cells. They affect mental acuity and physical mobility, physique and height, determine hair growth, voice tone, sexual desire and behavior. Thanks to the endocrine system, a person can adapt to strong temperature fluctuations, excess or lack of food, physical and emotional stress. The study of the physiological action of the endocrine glands made it possible to reveal the secrets of sexual function and the miracle of childbearing, and also to answer the question why some people are tall and others are short, some are full, others are thin, some are slow, others are agile, some are strong, others are weak.
In the normal state, there is a harmonious balance between the activity of the endocrine glands, the state of the nervous system and the response of target tissues (tissues that are affected). Any violation in each of these links quickly leads to deviations from the norm. Excessive or insufficient production of hormones causes various diseases, accompanied by profound chemical changes in the body.
What are hormones? According to the classical definition, hormones are secretion products of the endocrine glands that are released directly into the bloodstream and have a high physiological activity. Main endocrine glands mammals - pituitary, thyroid and parathyroid glands, adrenal cortex, adrenal medulla, pancreatic islet tissue, gonads (testes and ovaries), placenta and hormone-producing parts of the gastrointestinal tract. Some hormone-like compounds are also synthesized in the body. For example, studies of the hypothalamus have shown that a number of substances secreted by it are necessary for the release of pituitary hormones. These "releasing factors", or liberins, have been isolated from various regions of the hypothalamus. They enter the pituitary gland through a system of blood vessels connecting both structures. Since the hypothalamus is not a gland in its structure, and releasing factors seem to enter only the very closely located pituitary gland, these substances secreted by the hypothalamus can be considered hormones only with a broad understanding of this term.
Other questions are even more difficult. The kidneys secrete the enzyme renin into the bloodstream, which, through the activation of the angiotensin system (this system causes the expansion of blood vessels), stimulates the production of the adrenal hormone aldosterone. The regulation of aldosterone release by this system is very similar to how the hypothalamus stimulates the release of the pituitary hormone ACTH (adrenocorticotropic hormone, or corticotropin), which regulates the function of the adrenal glands. The kidneys also secrete erythropoietin, a hormonal substance that stimulates the production of red blood cells. Can the kidney be classified as an endocrine organ? All these examples prove that the classical definition of hormones and endocrine glands is not exhaustive enough.
The action of the hormone |
||
Growth hormone or growth hormone |
In children, it stimulates the growth of the body. Increases protein synthesis, helps cells absorb nutrients, enhances the breakdown of fats in adipose tissue. |
Increases, ensuring the breakdown of fats in adipose tissue and their use as an energy source for muscle contraction. |
Hormone that regulates the activity of the adrenal cortex or adrenocorticotropic hormone or andrenocorticotropin |
Enhances the secretion of adrenal hormones. |
Increases, since the activity of the adrenal glands is necessary for muscle work. |
Thyroid hormone or thyroid-stimulating hormone or thyrotropin |
Enhances the secretion of thyroid hormones. |
Probably increasing. |
A group of hormones that regulate the activity of the gonads, or gonadotropic hormones or gonadotropins |
Stimulates the functions of the gonads. |
It decreases, since the specific activity of the gonads is not required to perform muscle work. |
A hormone that regulates the activity of the mammary glands or luteotropic hormone or prolactin (often included in the group gonadotropic hormones) |
Stimulates the development of the corpus luteum (female endocrine gland, formed at the site of a mature follicle) in women and the release of testosterone (male sex hormone) in men. Causes the manifestation of maternal instinct. During pregnancy and lactation, it stimulates the production of milk by the mammary glands. |
It decreases because the changes caused by the hormone are not required to perform muscle work. |
The role of adrenal and pancreatic hormones thyroid gland in the regulation of carbohydrate metabolism.
ADRENAL, small flattened paired glands of yellowish color, located above the upper poles of both kidneys. The right and left adrenal glands differ in shape: the right is triangular, and the left is crescent-shaped. These are the endocrine glands, i.e. the substances (hormones) they secrete enter directly into the bloodstream and participate in the regulation of the body's vital functions. The average weight of one gland is from 3.5 to 5 g. Each gland consists of two anatomically and functionally different parts: the outer cortical and the inner medulla.
The cortical layer comes from the mesoderm (middle germ layer) of the embryo. The sex glands, the gonads, also develop from the same leaf. Like the gonads, the cells of the adrenal cortex secrete (secrete) sex steroids - hormones that are similar in chemical structure and biological action to the hormones of the sex glands. In addition to sex cells, cortical cells produce two more very important groups of hormones: mineralocorticoids (aldosterone and deoxycorticosterone) and glucocorticoids (cortisol, corticosterone, etc.).
Decreased secretion of adrenal hormones leads to a condition known as Addison's disease. These patients are treated with replacement therapy.
Excessive production of cortical hormones underlies the so-called. Cushing's syndrome. In this case, surgical removal of the adrenal tissue with excessive activity is sometimes performed, followed by the appointment of replacement doses of hormones.
Increased secretion of male sex steroids (androgens) is the cause of virilism - the appearance of masculine features in women. Usually this is a consequence of a tumor in the adrenal cortex, so the best treatment is removal of the tumor.
The medulla originates from the sympathetic ganglia of the nervous system of the embryo. The main hormones of the medulla are adrenaline and norepinephrine. Adrenaline was isolated by J. Abel in 1899; it was the first hormone obtained in a chemically pure form. It is a derivative of the amino acids tyrosine and phenylalanine. Norepinephrine, the precursor of adrenaline in the body, has a similar structure and differs from the latter only in the absence of one methyl group. The role of epinephrine and norepinephrine is to enhance the effects of the sympathetic nervous system; they increase heart rate and breathing, blood pressure, and also affect the complex functions of the nervous system itself.
Hormones of the adrenal cortex
Biology. The nervous system responds to many external influences (including stress) by sending nerve impulses to a special part of the brain - the hypothalamus. In response to these signals, the hypothalamus secretes corticoliberin, which is carried by the blood along the so-called. portal system directly to the pituitary gland (located at the base of the brain) and stimulates the secretion of corticotropin (adrenocorticotropic hormone, ACTH). The latter enters the general circulation and, once in the adrenal glands, in turn stimulates the production and secretion of cortisol by the adrenal cortex.
PANCREAS, digestive and endocrine glands. Found in all vertebrates except lampreys, hagfish and other primitive vertebrates. Elongated shape, in outline resembles a bunch of grapes.
Structure. In humans, the pancreas weighs from 80 to 90 g, is located along the posterior wall of the abdominal cavity and consists of several sections: the head, neck, body and tail. The head is on the right, in the bend of the duodenum - part small intestine- and directed downwards, while the rest of the gland lies horizontally and ends next to the spleen. The pancreas is made up of two types of tissue with completely different functions. Actually, the pancreatic tissue is made up of small lobules - acini, each of which is equipped with its own excretory duct. These small ducts merge into larger ones, which in turn flow into the duct of Wirsung, the main excretory duct of the pancreas. The lobules almost entirely consist of cells that secrete pancreatic juice (pancreatic juice, from Latin pancreas - pancreas). pancreatic juice contains digestive enzymes. From the lobules through the small excretory ducts, it enters the main duct, which flows into duodenum. The main pancreatic duct is located near the common bile duct and connects with it before flowing into the duodenum. Interspersed between the lobules are numerous groups of cells that do not have excretory ducts - the so-called. islets of Langerhans. Islet cells secrete the hormones insulin and glucagon.
Functions. The pancreas has both endocrine and exocrine functions, i.e. carries out internal and external secretion. The exocrine function of the gland is participation in digestion.
Digestion. The part of the gland involved in digestion secretes pancreatic juice through the main duct directly into the duodenum. It contains 4 enzymes necessary for digestion: amylase, which converts starch into sugar; trypsin and chymotrypsin are proteolytic (protein-splitting) enzymes; lipase, which breaks down fats; and rennin, curdling milk. Thus, pancreatic juice plays an important role in the digestion of essential nutrients.
endocrine functions. The islets of Langerhans function as endocrine glands (endocrine glands), releasing directly into the bloodstream glucagon and insulin, hormones that regulate carbohydrate metabolism. These hormones have the opposite effect: glucagon raises and insulin lowers blood sugar levels.
Diseases. Pancreatic diseases include acute or chronic inflammation (pancreatitis), atrophy, tumors, fat necrosis, cysts, sclerosis, and abscesses. Insufficient secretion of insulin leads to a decrease in the ability of cells to absorb carbohydrates, i.e. to diabetes. Nutritional disorders cause atrophy or fibrosis of the pancreas. The cause of acute pancreatitis is the action of secreted enzymes on the tissue of the gland itself.
Hormone |
The action of the hormone |
Changes in hormone secretion during moderate muscle activity |
thyroxine or tetraiodothyronine |
Practically does not change. |
|
It facilitates the penetration of sugar from the blood into the cells of muscles and adipose tissue, facilitates the penetration of amino acids from the blood into the cells, promotes the synthesis of protein and fats. Promotes the deposition of glucose in the store (in the liver). |
At the beginning of work, it increases, facilitating the penetration of glucose into cells, and then it decreases, as it causes changes that are opposite to those necessary for effective muscle activity. |
|
Glucagon |
It has an effect in many respects opposite to insulin. It enhances the breakdown of glucose chains in cells and the release of glucose from its storage sites into the blood. Stimulates the breakdown of fat in adipose tissue. |
It increases, ensuring the breakdown and release into the blood of carbohydrates and fats, which provide energy for muscle contraction. |
THYROID, endocrine gland in vertebrates and humans. The hormones it produces (thyroid hormones) affect reproduction, growth, tissue differentiation and metabolism; it is also believed that they activate migration processes in salmonids. The main function of the thyroid gland in humans is the regulation of metabolic processes, including oxygen consumption and the use of energy resources in cells. Increasing the amount of thyroid hormones speeds up the metabolism; deficiency causes it to slow down.
The structure of the thyroid gland in different vertebrates is different. In birds, for example, it consists of two small formations in the neck, while in most fish it is represented by small clusters of cells (follicles) in the pharynx. In humans, the thyroid gland is a dense, butterfly-like structure located just below the larynx (glottis). The two "wings" of this "butterfly", the lobes of the thyroid gland, usually about the size of a flattened peach pit, stretch upward on both sides of the trachea. The lobes are connected by a narrow strip of tissue (isthmus) that runs along the anterior surface of the trachea.
Production of hormones. The thyroid gland actively absorbs iodine from the blood, and also synthesizes a specific protein - thyroglobulin, which contains many residues of the amino acid tyrosine and is a precursor of gland hormones. Iodine binds to tyrosine in this protein, and the subsequent pairwise association (oxidative condensation) of iodinated tyrosine residues ultimately leads to the formation of thyroid hormones - triiodothyronine (T3) or tetraiodothyronine (T4). The latter is usually called thyroxine. Under the action of tissue enzymes, thyroglobulin breaks down, and free thyroid hormones enter the bloodstream. Their main form in the blood is T4. It consists of two-thirds (by weight) of iodine and is produced only in the thyroid gland. T3 contains one atom of iodine less, but 10 times more active than T4. Although some of it is secreted by the thyroid gland, it is mainly formed from T4 (by splitting off one iodine atom) in other tissues of the body, mainly in the liver and kidneys.
The amount of hormones produced by the thyroid gland is normally regulated by a feedback system, the links of which are the thyroid-stimulating hormone (TSH) of the pituitary gland and the thyroid hormones themselves. When TSH levels rise, the thyroid gland produces and secretes more hormones, and an increase in their level suppresses the production and secretion of pituitary TSH.
The third thyroid hormone, calcitonin, is involved in the regulation of calcium levels in the blood.
The action of the hormone |
Changes in hormone secretion during moderate muscle activity |
|
thyroxine or tetraiodothyronine |
It enhances the processes of oxidation of fats, carbohydrates and proteins in cells, thus accelerating the metabolism in the body. Increases the excitability of the central nervous system. |
Practically does not change. |
Triiodothyronine |
The action is in many ways similar to thyroxine. |
Practically does not change. |
thyrocalcitonin |
Regulates the exchange of calcium in the body, reducing its content in the blood, and increasing its content in bone tissue (has an effect opposite to the parathyroid hormone of the parathyroid glands). A decrease in the level of calcium in the blood reduces the excitability of the central nervous system. |
Increases with significant fatigue occurring during prolonged muscular activity. |
clinical disorders. In most regions of the world, ordinary food provides the body with enough iodine for normal production of thyroid hormones. However, in areas where there is a deficiency of iodine in the soil and, of course, food, the use of iodized salt can solve this problem.
Insufficient production of thyroid hormones leads to hypothyroidism, or myxedema. In hypothyroidism, the thyroid gland may be enlarged (goiter), but may disappear completely. This condition is more common in women than in men, and is often the result of damage to the thyroid gland of one's own immune system body (autoantibodies). Drowsiness and cold intolerance are usually noted. AT severe cases sometimes a coma develops and death may occur. For the treatment of hypothyroidism, preparations of the dried thyroid gland of animals are used, and more recently, synthetic T4 tablets.
Excess secretion of thyroid hormones leads to hyperthyroidism, or thyrotoxicosis. The most common form of hyperthyroidism is diffuse toxic goiter, or Graves' disease, which is described in the article GOI.
Thyroid cancer usually requires surgical treatment, sometimes combined with radioactive iodine administration. This type of cancer is more common in people who have had radiation to the head and neck.
Features of hormonal regulation of carbohydrate metabolism during muscle activity.
Energy is expended for any process of vital activity of an organism. This energy is formed as a result of the breakdown of various chemicals - carbohydrates, fats (less often - proteins) that enter the body with food.
Carbohydrates enter the body with plant foods and, to a lesser extent, with animal foods. In addition, they are synthesized in it from the breakdown products of amino acids and fats. Carbohydrates are an important component of a living organism, although their amount in the body is much less than proteins and fats - only about 2% of the dry matter of the body.
If the energy stored in the chemical bonds of substances supplied with food is greater than the body's energy consumption for vital processes, part of the energy is deposited in the reserve. In mammals, adipose tissue is the reserve source of energy. Any substance, the amount of which in the body exceeds the required level, turns into fats and is deposited in the reserve in adipose tissue. In other words, if a person consumes more food than he expends energy, then he gets fat. If the amount of energy coming from food is less than the energy expenditure of the body, then the body is forced to take the missing energy from the reserves. Initially, the body spends the carbohydrates in the cells and in the blood. The process of carbohydrate breakdown is quite easy and fast, in contrast to the complex and lengthy process of fat breakdown. When the amount of carbohydrates reaches a certain minimum, the body begins to break down fats. Thus, if a person eats less than he expends energy, he loses weight.
In some cases, when extremely little or no energy is supplied with food (starvation), and the energy demands of the body are high (more or less intense muscle activity), the body does not expend energy on the complex process of splitting fats. In these cases, it is easier for the body to break down certain types of low molecular weight proteins. These proteins include, first of all, immune proteins. Cleavage of immune proteins in blood plasma significantly reduces the body's immune defenses. Therefore, with an active lifestyle, fasting can be very dangerous.
The influence of the central nervous system on carbohydrate metabolism is carried out mainly through sympathetic innervation. Irritation of the sympathetic nerves enhances the formation of adrenaline in the adrenal glands. It causes the breakdown of glycogen in the liver and skeletal muscles and, in connection with this, an increase in the concentration of glucose in the blood. The pancreatic hormone glucagon also stimulates these processes. The pancreatic hormone insulin is an antagonist of adrenaline and glucagon. It directly affects the carbohydrate metabolism of liver cells, activates the synthesis of glycogen and thereby contributes to its deposition. The hormones of the adrenal, thyroid, and pituitary glands are involved in the regulation of carbohydrate metabolism.
Energy expenditure is usually measured in kilocalories (kcal). There are other values for estimating energy costs.
Carbohydrates serve as the main source of energy in the body. When 1 g of carbohydrates are oxidized, 4.1 kcal of energy is released. Much less oxygen is required to oxidize carbohydrates than to oxidize fats. This especially increases the role of carbohydrates in muscle activity. Their significance as a source of energy is confirmed by the fact that with a decrease in the concentration of glucose in the blood, physical performance is sharply reduced. Great importance carbohydrates are necessary for the normal functioning of the nervous system.
Basal metabolism is the body's energy expenditure associated with maintaining a minimum level of vital activity under standard conditions during wakefulness.
Even in a state of absolute rest, deep sleep, anesthesia or coma, the body expends energy on the following vital processes:
- activity of constantly working organs - respiratory muscles, heart, kidneys, liver, brain
- maintaining a vital biochemical imbalance between the internal composition of the cell and the composition of the intercellular fluid
- ensuring intracellular processes of respiration, constantly ongoing synthesis of vital substances
- maintaining a minimum level of muscle tone
- ensuring a constantly ongoing process of cell division
- other processes
The value of the basic metabolism is determined in the morning on an empty stomach at rest after sleep at an ambient temperature of 18-200 C.
The main factors on which the level of basic metabolism depends
- Age. The relative basal metabolism (in terms of body weight) in children is higher than in adults, in middle-aged people it is higher than in the elderly.
- Growth. The greater the growth, the higher the basal metabolic rate.
- Body mass. The greater the mass, the higher the basal metabolic rate.
- Floor. In men, the basal metabolism is higher than in women, even with the same height, weight and age.
In a middle-aged man - 35 years old, average weight - 70 kg, average height - 165 cm, the main metabolism is approximately 1,700 kilocalories (kcal) per day. In a woman under the same conditions, the basal metabolism is approximately 5-10% lower (1,530 kcal).
The activity of the thyroid gland also significantly affects the magnitude of the basal metabolism. In cases of diseases associated with an increase in its function - Basedow's disease, hyperthyroidism - the basal metabolism increases disproportionately. In diseases associated with inhibition of the activity of the thyroid gland - myxedema, hypothyroidism - the basal metabolism is disproportionately reduced. Similarly, the level of basal metabolism is affected by the activity of the pituitary gland (to a significant extent) and the gonads (to a much lesser extent).
Food contains mainly complex carbohydrates, which are broken down in the intestines and absorbed into the blood, mainly in the form of glucose. Small amounts of glucose are found in all tissues. Its concentration in the blood ranges from 0.08 to 0.12%. Entering the liver and muscles, glucose is used there for oxidative processes, and also turns into glycogen and is deposited in the form of reserves.
During fasting, liver glycogen stores and blood glucose levels decrease. The same thing happens with long and strenuous physical work without additional intake of carbohydrates. A decrease in blood glucose concentration below 0.07% is called hypoglycemia, and an increase above 0.12% is called hyperglycemia.
With hypoglycemia, muscle weakness, a feeling of hunger appear, body temperature drops. Violation of the activity of the nervous system is manifested in this case in the occurrence of convulsions, stupefaction and loss of consciousness.
Hyperglycemia can occur after eating a meal rich in easily digestible carbohydrates, with emotional arousal, as well as with diseases of the pancreas or when it is removed in animals for experimental purposes. Excess glucose is excreted from the blood by the kidneys (glycosuria). In a healthy person, this can be observed after taking 150-200 g of sugar on an empty stomach.
The liver contains about 10% glycogen, in skeletal muscles no more than 2%. Its total reserves in the body average 350 g. With a decrease in the concentration of glucose in the blood, there is an intensive breakdown of liver glycogen and the release of glucose into the blood. Thanks to this, a constant level of glucose in the blood is maintained and the need for it of other organs is satisfied.
In the body there is a constant exchange of glucose between the liver, blood, muscles, brains and other organs. The main consumer of glucose is skeletal muscle. The breakdown of carbohydrates in them is carried out according to the type of anaerobic and aerobic reactions. One of the breakdown products of carbohydrates is lactic acid.
Carbohydrate reserves are especially intensively used during physical work. However, they are never completely exhausted. With a decrease in glycogen stores in the liver, its further breakdown stops, which leads to a decrease in the concentration of glucose in the blood to 0.05-0.06%, and in some cases to 0.04-0.038%. In the latter case, muscular activity cannot continue. Thus, a decrease in blood glucose is one of the factors that reduce the body's performance during prolonged and intense muscle activity. With such work, it is necessary to replenish carbohydrate reserves in the body, which is achieved by increasing carbohydrates in the diet, additionally introducing them before starting work and immediately during its implementation. Saturation of the body with carbohydrates helps to maintain a constant concentration of glucose in the blood, which is necessary to maintain a high human performance.
The effect of carbohydrate intake on performance has been established by laboratory experiments and observations during sports activities. The effect of carbohydrates taken before work, ceteris paribus, depends on the amount and time of intake.
The level of basic metabolism is regulated by the nervous system and the system of endocrine glands.
Additional energy costs - the body's energy costs for the performance of any acts of vital activity in excess of the basic metabolism.
Additional energy expenditure increases after eating - this is the energy expended by the body, not the processes of digestion.
When taking carbohydrate foods, energy expenditure increases by 5-10%, fat - by 10-15%, when taking protein foods - by 20-30%.
To a small extent, energy consumption increases with mental activity. Even extremely intense mental work causes an increase in energy consumption by only 2-3%. The feeling of hunger that a person may experience in this case is due to the fact that the brain, in conditions of intense mental activity, requires a large amount of pure glucose. Taking a cup of sweet tea fully satisfies the brain's glucose requirements under these conditions. Additional energy costs increase under the influence of emotional experiences (on average by 11-19%).
An increase in the energy expenditure of the body is recorded with a decrease in temperature environment. Under these conditions, the body increases the intensity of decay processes several times in order to release the energy used to maintain a constant body temperature.
The body's energy expenditure increases most significantly during muscle activity. Energy expenditure is the higher, the more intense the muscular work done by the body. For example, running at maximum speed causes energy expenditure of the body up to 3-4 kcal per second. But since such activity can last only a few seconds, the total energy consumption is negligible (about 20-30 kcal). At the same time, low-intensity running for several tens of minutes with relative energy consumption of 0.4-0.3 kcal per second will cause body losses from 500 kcal to 2000 kcal and more, depending on the duration of the run.
According to modern experts (Vereshchagin L.I., 1990), in order to maintain their health, a person must spend at least 1200 kcal of energy on muscle work during the day.
When performing muscular activity in conditions of emotional experiences (game activity, martial arts, activities associated with risk, performances in competitions), the body expends energy both to perform the activity itself and to provide emotional experiences. Therefore, running a distance in training will cause less energy expenditure than the same activity in a competition.
Additional energy expenditure during certain types of physical exercise
An exercise |
Additional energy consumption (kcal) |
Ski race: |
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Ice skating: |
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Swimming: |
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Additional energy expenditure of the body (in excess of the basic metabolism)
LITERATURE
- N.N. Yakovlev. "Biochemistry": textbook for IFC. Mn. FIS 1974.
- N.I. Volkov, N.I. Nensin. "Biochemistry of muscular activity" textbook for universities. Kyiv 2000.
- J.H. Wilmore, D.L. Bones. "Physiology of sports and motor activity". Kyiv: Olympic Literature 1997.
- N.I Yakovlev "Chemistry of motion". Leningrad: Nauka 1983.
- V.V. Vasiliev "Carbohydrate metabolism and its regulation".
Regulation of carbohydrate metabolism is carried out at all its stages by the nervous system and hormones. In addition, activity enzymes a separate pathway of carbohydrate metabolism is regulated by the "feedback" principle, which is based on the allosteric mechanism of the interaction of the enzyme with the effector. Regulation of carbohydrate metabolism is carried out at all its stages by the nervous system and hormones. In addition, activity enzymes a separate pathway of carbohydrate metabolism is regulated by the "feedback" principle, which is based on the allosteric mechanism of the interaction of the enzyme with the effector. Allosteric effectors include reaction end products, substrates, some metabolites, and adenyl mononucleotides. The most important role in focus carbohydrate metabolism (synthesis or breakdown of carbohydrates) is played by the ratio of coenzymes NAD + / NADH ∙ H + and the energy potential of the cell.
The constancy of the level of glucose in the blood is the most important condition for maintaining the normal functioning of the body. Normoglycemia is the result of the coordinated work of the nervous system, hormones and liver.
Liver- the only organ that stores glucose (in the form of glycogen) for the needs of the whole organism. Due to the active phosphatase of glucose-6-phosphate, hepatocytes are able to form free glucose, which, unlike its phosphorylated forms, can penetrate through the cell membrane into the general circulation.
Of the hormones, an outstanding role is played by insulin. Insulin has its effect only on insulin-dependent tissues, primarily on muscle and fat. The brain, lymphatic tissue, erythrocytes are insulin-independent. Unlike other organs, the action of insulin is not associated with the receptor mechanisms of its effect on hepatocyte metabolism. Although glucose freely enters the liver cells, this is possible only if its concentration in the blood is increased. In hypoglycemia, on the contrary, the liver releases glucose into the blood (even though high level serum insulin).
The most significant effect of insulin on the body is the reduction of normal or elevated blood glucose levels - up to the development of hypoglycemic shock with the introduction of high doses of insulin. The level of glucose in the blood decreases as a result of: 1. Accelerating the entry of glucose into cells. 2. Increasing the use of glucose by cells.
1. Insulin accelerates the entry of monosaccharides into insulin-dependent tissues, especially glucose (as well as sugars of a similar configuration in position C 1 -C 3), but not fructose. Binding of insulin to its receptor on the plasma membrane results in the movement of storage glucose transport proteins ( glut 4) from intracellular depots and their incorporation into the membrane.
2. Insulin activates the use of glucose by cells by:
activation and induction of the synthesis of key enzymes of glycolysis (glucokinase, phosphofructokinase, pyruvate kinase).
· Increased incorporation of glucose into the pentose phosphate pathway (activation of glucose-6-phosphate and 6-phosphogluconate dehydrogenases).
Increase in glycogen synthesis by stimulating the formation of glucose-6-phosphate and activating glycogen synthase (at the same time, insulin inhibits glycogen phosphorylase).
Inhibition of the activity of key enzymes of gluconeogenesis (pyruvate carboxylase, phosphoenol PVA carboxykinase, biphosphatase, glucose-6-phosphatase) and repression of their synthesis (the fact of repression of the phosphoenol PVA carboxykinase gene was established).
Other hormones tend to increase blood glucose levels.
Glucagon and a adrenaline lead to an increase in glycemia by activating glycogenolysis in the liver (activation of glycogen phosphorylase), however, unlike adrenaline, glucagon does not affect glycogen phosphorylase muscles. In addition, glucagon activates gluconeogenesis in the liver, which also results in an increase in the concentration of glucose in the blood.
Glucocorticoids contribute to an increase in blood glucose levels by stimulating gluconeogenesis (accelerating the catabolism of proteins in muscle and lymphoid tissues, these hormones increase the content of amino acids in the blood, which, entering the liver, become substrates of gluconeogenesis). In addition, glucocorticoids interfere with the utilization of glucose by body cells.
A growth hormone causes an increase in glycemia indirectly: by stimulating the breakdown of lipids, it leads to an increase in the level of fatty acids in the blood and cells, thereby reducing the need for glucose in the latter ( fatty acids - inhibitors of the use of glucose by cells).
thyroxin, especially produced in excess quantities in hyperthyroidism, it also contributes to an increase in blood glucose levels (due to increased glycogenolysis).
At normal glucose levels in the blood, the kidneys completely reabsorb it and sugar in the urine is not detected. However, if glycemia exceeds 9-10 mmol / l ( renal threshold ), then it appears glycosuria . With some kidney damage, glucose can be detected in the urine and with normoglycemia.
Testing the body's ability to regulate blood glucose ( glucose tolerance ) is used to diagnose diabetes when administering oral glucose tolerance test:
The first blood sample is taken on an empty stomach after an overnight fast. Then the patient for 5 minutes. give to drink a solution of glucose (75 g of glucose dissolved in 300 ml of water). Thereafter every 30 min. for 2 hours determine the content of glucose in the blood
in biological chemistry
for students of _____2nd_____ year of ___medical ___________________ faculty
Topic: ___ Carbohydrates 4. Pathology of carbohydrate metabolism
Time__90 min___________________
Learning goal:
1. To form ideas about the molecular mechanisms of the main disorders of carbohydrate metabolism.
LITERATURE
1. Human biochemistry:, R. Murray, D. Grenner, P. Meyes, V. Rodwell. - M. book, 2004. - v. 1. p.
2. Fundamentals of biochemistry: A. White, F. Hendler, E. Smith, R. Hill, I. Leman.-M. book,
1981, vol. -.2,.s. 639-641,
3. Visual biochemistry: Kolman., Rem K.-G-M.book 2004.
4. Biochemical basics ... under. ed. corresponding member RAS E.S. Severin. M. Medicine, 2000.-p. 179-205.
MATERIAL SUPPORT
1.Multimedia presentation
CALCULATION OF STUDY TIME
The main energy resources of a living organism - carbohydrates and fats have a high potential energy reserve, easily extracted from them in cells with the help of enzymatic catabolic transformations. The energy released during the biological oxidation of carbohydrate and fat metabolism, as well as glycolysis, is converted to a large extent into the chemical energy of the phosphate bonds of the synthesized ATP. The chemical energy of macroergic bonds accumulated in ATP, in turn, is spent on different kind cellular work - the creation and maintenance of electrochemical gradients, muscle contraction, secretory and some transport processes, protein biosynthesis, fatty acids, etc. In addition to the "fuel" function, carbohydrates and fats, along with proteins, play the role of important suppliers of building, plastic materials that are part of the basic structures of the cell - nucleic acids, simple proteins, glycoproteins, a number of lipids, etc. Synthesized due to the breakdown of carbohydrates and fats, ATP not only provides cells with the energy necessary for work, but is also a source of cAMP formation, and also participates in the regulation of the activity of many enzymes, the state of structural proteins, ensuring their phosphorylation.
Carbohydrate and lipid substrates that are directly utilized by cells are monosaccharides (primarily glucose) and non-esterified fatty acids (NEFA), as well as ketone bodies in some tissues. Their sources are foods absorbed from the intestines, deposited in organs in the form of carbohydrate glycogen and lipids in the form of neutral fats, as well as non-carbohydrate precursors, mainly amino acids and glycerol, forming carbohydrates (gluconeogenesis). The depositing organs in vertebrates include the liver and adipose (adipose) tissue, while the organs of gluconeogenesis are the liver and kidneys. In insects, the depositing organ is the fat body. In addition, some reserve or other products stored or formed in a working cell can also be sources of glucose and NEFA. Different ways and stages of carbohydrate and fat metabolism are interconnected by numerous mutual influences. The direction and intensity of these metabolic processes depend on a number of external and internal factors. These include, in particular, the quantity and quality of food consumed and the rhythms of its entry into the body, the level of muscle and nervous activity, etc.
The animal organism adapts to the nature of the diet, to the nervous or muscular load with the help of a complex set of coordinating mechanisms. Thus, the control of the course of various reactions of carbohydrate and lipid metabolism is carried out at the cell level by the concentrations of the corresponding substrates and enzymes, as well as by the degree of accumulation of the products of a particular reaction. These control mechanisms are related to self-regulation mechanisms and are implemented both in unicellular and multicellular organisms. In the latter, the regulation of the utilization of carbohydrates and fats can occur at the level of intercellular interactions. In particular, both types of metabolism are reciprocally mutually controlled: NEFA in muscles inhibit the breakdown of glucose, while glucose breakdown products in adipose tissue inhibit the formation of NEFA. In the most highly organized animals, a special intercellular mechanism for the regulation of interstitial metabolism appears, determined by the appearance in the process of evolution endocrine system, which is of paramount importance in the control of metabolic processes of the whole organism.
Among the hormones involved in the regulation of fat and carbohydrate metabolism in vertebrates, the central place is occupied by the following: hormones of the gastrointestinal tract, which control the digestion of food and the absorption of digestive products into the blood; insulin and glucagon are specific regulators of the interstitial metabolism of carbohydrates and lipids; STH and functionally related "somatomedins" and CIF, glucocorticoids, ACTH and adrenaline are factors of nonspecific adaptation. It should be noted that many of these hormones are also directly involved in the regulation of protein metabolism (see Chapter 9). The rate of secretion of these hormones and the realization of their effects on tissues are interrelated.
We cannot specifically dwell on the functioning of the hormonal factors of the gastrointestinal tract secreted during the neurohumoral phase of sap secretion. Their main effects are well known from the course of general human and animal physiology and, in addition, they have already been quite fully mentioned in Chap. 3. Let us dwell in more detail on the endocrine regulation of the interstitial metabolism of carbohydrates and fats.
Hormones and regulation of interstitial carbohydrate metabolism. An integral indicator of the balance of carbohydrate metabolism in the body of vertebrates is the concentration of glucose in the blood. This indicator is stable and in mammals is approximately 100 mg% (5 mmol / l). Its deviations from the norm usually do not exceed ± 30%. The level of glucose in the blood depends, on the one hand, on the influx of monosaccharide into the blood, mainly from the intestines, liver, and kidneys, and, on the other hand, on its outflow into working and depositing tissues (Fig. 2).
The influx of glucose from the liver and kidneys is determined by the ratio of the activities of the glycogen phosphorylase and glycogen synthetase reactions in the liver, the ratio of the intensity of glucose breakdown and the intensity of gluconeogenesis in the liver and partly in the kidney. The entry of glucose into the blood directly correlates with the levels of the phosphorylase reaction and the processes of gluconeogenesis. The outflow of glucose from blood to tissues is directly dependent on the rate of its transport to muscle, adipose and lymphoid cells, the membranes of which create a barrier to the penetration of glucose into them (recall that the membranes of liver, brain and kidney cells are easily permeable to monosaccharide); metabolic utilization of glucose, which in turn depends on the permeability of membranes to it and on the activity of key enzymes of its breakdown; conversion of glucose to glycogen in liver cells (Levin et al., 1955; Newsholm and Randle, 1964; Foa, 1972). All these processes associated with the transport and metabolism of glucose are directly controlled by a complex of hormonal factors.
Fig.2. Ways to Maintain Dynamic Blood Glucose Balance Muscle and adipose cell membranes have a "barrier" to glucose transport; Gl-b-f -- glucose-b-phosphate.
Hormonal regulators of carbohydrate metabolism according to their effect on the general direction of metabolism and the level of glycemia can be divided into two types. The first type of hormones stimulates the utilization of glucose by tissues and its deposition in the form of glycogen, but inhibits gluconeogenesis, and, consequently, causes a decrease in the concentration of glucose in the blood. The hormone of this type of action is insulin. The second type of hormone stimulates the breakdown of glycogen and gluconeogenesis, and therefore causes an increase in blood glucose. These hormones include glucagon (as well as secretin and VIP) and adrenaline. Hormones of the third type stimulate gluconeogenesis in the liver, inhibit the utilization of glucose by various cells, and although they increase the formation of glycogen by hepatocytes, as a result of the predominance of the first two effects, as a rule, they also increase blood glucose levels. The hormones of this type include glucocorticoids and growth hormone - "somatomedins". At the same time, having a unidirectional effect on the processes of gluconeogenesis, glycogen synthesis and glycolysis, glucocorticoids and growth hormone - "somatomedins" differently affect the permeability of cell membranes of muscle and adipose tissue to glucose.
In terms of the direction of action on the concentration of glucose in the blood, insulin is a hypoglycemic hormone (“rest and satiety” hormone), while hormones of the second and third types are hyperglycemic (“stress and starvation” hormones) (Fig. 3).
Figure 3. Hormonal regulation of carbohydrate homeostasis: solid arrows indicate stimulation of the effect, dotted arrows indicate inhibition.
Insulin can be called the hormone of absorption and storage of carbohydrates. One of the reasons for the increased utilization of glucose in tissues is the stimulation of glycolysis. It is carried out, possibly, at the level of activation of the key enzymes of glycolysis, hexokinase, especially one of its four known isoforms, hexokinase II, and glucokinase (Weber, 1966; Ilyin, 1966, 1968). Apparently, the acceleration of the pentose phosphate pathway at the stage of the glucose-6-phosphate dehydrogenase reaction also plays a certain role in the stimulation of glucose catabolism by insulin (Leites and Lapteva, 1967). It is believed that hormonal induction of the specific hepatic enzyme glucokinase, which selectively phosphorylates glucose at high concentrations, plays an important role in stimulating glucose uptake by the liver during food hyperglycemia under the influence of insulin.
The main reason for the stimulation of glucose utilization by muscle and fat cells is primarily a selective increase in the permeability of cell membranes to the monosaccharide (Lunsgaard, 1939; Levin, 1950). In this way, an increase in the concentration of substrates for the hexokinase reaction and the pentose phosphate pathway is achieved.
Increased glycolysis under the influence of insulin in skeletal muscles and myocardium plays a significant role in the accumulation of ATP and ensuring the performance of muscle cells. In the liver, an increase in glycolysis is apparently important not so much for increasing the incorporation of pyruvate into the tissue respiration system, but for the accumulation of acetyl-CoA and malonyl-CoA as precursors for the formation of polyhydric fatty acids, and, consequently, triglycerides (Newsholm, Start, 1973). Glycerophosphate formed during glycolysis is also included in the synthesis of neutral fat. In addition, in the liver, and especially in the adipose tissue, to increase the level of lipogenesis from glucose, an important role is played by the hormone stimulation of the glucose-6-phosphate dehydrogenase reaction, leading to the formation of NADPH, a reducing cofactor necessary for the biosynthesis of fatty acids and glycerophosphate. At the same time, in mammals, only 3-5% of absorbed glucose is converted into hepatic glycogen, and more than 30% accumulates in the form of fat deposited in depositing organs.
Thus, the main direction of action of insulin on glycolysis and the pentose phosphate pathway in the liver and especially in adipose tissue is to ensure the formation of triglycerides. In mammals and birds in adipocytes, and in lower vertebrates in hepatocytes, glucose is one of the main sources of deposited triglycerides. In these cases, the physiological meaning of the hormonal stimulation of carbohydrate utilization is reduced to a large extent to the stimulation of lipid deposition. At the same time, insulin directly affects the synthesis of glycogen - the deposited form of carbohydrates - not only in the liver, but also in muscles, kidneys, and, possibly, adipose tissue.
In terms of its effect on carbohydrate metabolism, adrenaline is close to glucagon, since the mechanism of mediation of their effects is the adenylate cyclase complex (Robizon et al., 1971). Adrenaline, like glucagon, enhances the breakdown of glycogen and the processes of gluconeogenesis. At physiological concentrations, glucagon is predominantly recep- ted by the liver and adipose tissue, and adrenaline by muscles (primarily the myocardium) and adipose tissue. Therefore, for glucagon, to a greater extent, and for adrenaline, to a lesser extent, delayed stimulation of gluconeogenetic processes is characteristic. However, for adrenaline, to a much greater extent than for glucagon, an increase in glycogenolysis is typical and, apparently, as a result of this, glycolysis and respiration in the muscles. In terms of not mechanisms, but a general effect on glycolytic processes in muscle cells, adrenaline is partly a synergist of insulin, not glucagon. Apparently, insulin and glucagon are mostly nutritional hormones, and adrenaline is a stress hormone.
Currently, a number of biochemical mechanisms underlying the action of hormones on lipid metabolism have been established.
It is known that prolonged negative emotional stress, accompanied by an increase in the release of catecholamines into the bloodstream, can cause noticeable weight loss. It is appropriate to recall that the adipose tissue is abundantly innervated by the fibers of the sympathetic nervous system, the excitation of these fibers is accompanied by the release of norepinephrine directly into the adipose tissue. Adrenaline and norepinephrine increase the rate of lipolysis in adipose tissue; as a result, the mobilization of fatty acids from fat depots is enhanced and the content of non-esterified fatty acids in the blood plasma increases. As noted, tissue lipases (triglyceride lipase) exist in two interconvertible forms, one of which is phosphorylated and catalytically active, and the other is non-phosphorylated and inactive. Adrenaline stimulates cAMP synthesis through adenylate cyclase. In turn, cAMP activates the corresponding protein kinase, which promotes lipase phosphorylation, i.e. formation of its active form. It should be noted that the effect of glucagon on the lipolytic system is similar to that of catecholamines.
There is no doubt that the secret of the anterior pituitary gland, in particular somatotropic hormone, has an effect on lipid metabolism. Hypofunction of the gland leads to the deposition of fat in the body, pituitary obesity occurs. On the contrary, increased production of growth hormone stimulates lipolysis, and the content of fatty acids in the blood plasma increases. It has been proven that the stimulation of GH lipolysis is blocked by inhibitors of mRNA synthesis. In addition, it is known that the effect of growth hormone on lipolysis is characterized by the presence of a lag phase lasting about 1 hour, while adrenaline stimulates lipolysis almost instantly. In other words, it can be considered that the primary effect of these two types of hormones on lipolysis is manifested in different ways. Adrenaline stimulates the activity of adenylate cyclase, and growth hormone induces the synthesis of this enzyme. The specific mechanism by which GH selectively increases adenylate cyclase synthesis is still unknown.
Insulin has an opposite effect to adrenaline and glucagon on lipolysis and fatty acid mobilization. Insulin has recently been shown to stimulate phosphodiesterase activity in adipose tissue. Phosphodiesterase plays an important role in maintaining a constant level of cAMP in tissues; therefore, an increase in insulin content should increase the activity of phosphodiesterase, which in turn leads to a decrease in the concentration of cAMP in the cell, and, consequently, to the formation of an active form of lipase.
Undoubtedly, other hormones, in particular thyroxine, sex hormones, also affect lipid metabolism. For example, it is known that the removal of the gonads (castration) causes excessive deposition of fat in animals. However, the information that we have does not yet give grounds to speak with confidence about the specific mechanism of their action on lipid metabolism.
Thyroid hormones thyroxine (T3) is involved in the hormonal regulation of protein metabolism; it enhances protein synthesis; Conversely, high concentrations of T3 inhibit protein synthesis; growth hormone, insulin testosterone, estrogen increase protein breakdown, especially in muscle and lymphoid tissues, but stimulate protein synthesis in the liver.
The regulation of water-salt metabolism occurs in the neuro-hormonal way. When the osmotic concentration of blood changes, special sensitive formations (osmoreceptors) are excited, information from which is transmitted to the center, nervous system, and from it to the posterior lobe of the pituitary gland. With an increase in the osmotic concentration of blood, the release of antidiuretic hormone increases, which reduces the release of water in the urine; with an excess of water in the body, the secretion of this hormone decreases and its excretion by the kidneys increases. The constancy of the volume of body fluids is ensured by a special system of regulation, the receptors of which react to changes in the blood filling of large vessels, heart cavities, etc.; as a result, the secretion of hormones is reflexively stimulated, under the influence of which the kidneys change the excretion of water and sodium salts from the body. The most important hormones in the regulation of water metabolism are vasopressin and glucocorticoids, sodium - aldosterone and angiotensin, calcium - parathyroid hormone and calcitonin.
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