Hereditary diseases of carbohydrate metabolism
Jun 16, 2018
Carbohydrates are complex organic compounds that perform a number of important functions in the human body. Carbohydrates, consisting of one molecule, are called monosaccharides;of two bound molecules, disaccharides;of several molecules linked together, polysaccharides;consisting of several simple carbohydrates - oligosaccharides. The main monosaccharides of the human body are glucose, fructose, galactose and ribose. Disaccharides and oligosaccharides are part of a variety of food products. In addition, polysaccharides are common in the plant and animal world. The most important function of carbohydrates in the human body is to provide energy for all the processes occurring in it. Carbohydrates are also used as a building material, being a component of the basic substance of connective, bone and cartilaginous tissues. They perform a number of specific functions, in particular, they are structural elements of the glands of the human body( for example, salivary glands).Carbohydrates such as ribose and deoxyribose are the main component of RNA and DNA, respectively. A substance such as glucuronic acid is a glucose derivative and is involved in the process of neutralizing a variety of toxic substances in the body, and carbohydrate heparin is involved in the process of blood coagulation. The involvement of carbohydrates is proven in the protective reactions of the body's immune system. In the human body, oligo- and polysaccharides are supplied with food, which in this form can not be absorbed. In this connection, they undergo decomposition into monosaccharides under the influence of digestive juices in the gastrointestinal tract. In this form, they are absorbed in the intestine, then enter the bloodstream, thence to the liver, where they undergo further chemical transformations or accumulate in the tissues of the organ as stocks. Carbohydrates take part in the metabolism, turning, if necessary, into amino acids or fats.
In the blood of an adult human carbohydrate fructose is usually not found, but in the prenatal period it is a normal part of the fetal blood. This is due to the peculiarity of the metabolism in this age period. The exchange of glucose after its absorption in the intestine is determined by the body's needs for energy, as well as the supply of tissues with oxygen. With a lack of energy, glucose breaks down to lactic acid, and in the absence of oxygen in the tissues at this stage, glucose exchange ceases. In conditions of sufficient oxygen in the tissues of the human body, a further process of decomposition of glucose takes place to the final products, which are carbon dioxide and water. Both the disintegration of glycogen in the liver and the oxidation of lactic acid in the absence of sufficient oxygen are directed at compensating the energy expenditure of the organism. The process of decomposition of glycogen in the absence of oxygen is accompanied by the formation of a certain amount of energy used for the life of the organism. The conversion of glucose into lactic acid is also accompanied by the release of energy. This process takes place with the participation of 13 enzymes. The process of splitting glucose to carbon dioxide and water leads to the formation of an amount of energy that is 15 times greater than the amount of energy produced by the decomposition of liver glycogen in the absence of oxygen in the tissues of the body. The process of anoxic cleavage of glycogen is the more ancient mechanism of providing the human body with energy.
The content of glucose( sugar) in the blood is determined by some factors, including: the amount of glucose coming from the intestine, the intake of glucose into the blood from the organs that are its depot( mainly from the liver), the formation of glucose from other metabolic products. The amount of sugar in the blood is regulated by hormones, the main of which is the hormone of the pancreas - insulin. This hormone promotes the formation of glucose from a substance such as glycogen. The latter accumulates in the liver and, if necessary, undergoes reverse transformations, as a result of which glucose is again formed. In addition, insulin promotes the entry of glucose into various cells of the body, where as a result of numerous transformations, energy is generated, which is necessary for the realization of vital processes. When there is a lack of basic substances, from which glucose is formed, hormones are released from the adrenals, triggering the mechanisms of glucose formation from other initial substances. Insulin increases the use of glucose by peripheral tissues, reduces blood sugar, the glycogen content in the liver and increases its content in the muscles.
Another pancreatic hormone, glucagon, also has a multifaceted effect on glucose metabolism, and its effect is largely similar to that of adrenaline. Under the influence of glucagon and adrenaline, the decomposition of glycogen in the liver increases, but the absorption of glucose by tissues remains unchanged, as a result of which the sugar content in the blood rises. Thyroid hormones increase the intensity of metabolism and mobilize carbohydrates from the depot, although there is no influence on blood sugar. Although growth hormone( somatotropin) inhibits the formation of glucose from other source substances and simultaneously enhances its formation from liver glycogen, the level of glucose in the blood does not change. In a newborn child, the process of regulating carbohydrate metabolism has not yet been fully developed, which explains the decrease in blood sugar in the first days after birth. As a rule, the restoration of normal glucose level occurs on the 5th-10th day of a child's life. The reason for the reduced amount of glucose in the blood of newborns is the insufficient maturity of the mechanisms of its formation from liver glycogen. Of great importance is also the restructuring of the endocrine system that occurs in the first days of life. The intake or formation of glucose at certain times of the day can exceed the energy demands of the body at this point in time, and in this case it is stored in the liver cells in the form of glycogen. Reducing blood glucose serves as a signal for the reverse formation of glucose from glycogen.
The methods for qualitative and quantitative determination of carbohydrates in biological fluids of the body, the main one of which is blood, are of great importance for the detection of hereditary carbohydrate metabolism. For the purpose of rapid determination of glucose in urine, special indicator strips of paper are used. However, this method is only relatively accurate due to the fact that it determines only the presence of glucose and its approximate amount. These data are obtained by changing the color of the indicator strip after placing it in the urine of the subject.
To determine the diseases of glycogen storage, load test is of great importance. In this case, the researcher is asked to drink a solution of galactose with a certain amount of it, after which the glucose content in the blood is determined. In some cases, to clarify the type of disease, it is necessary to study the activity of enzymes that take part in the exchange of glucose. These enzymes are found in the muscles, liver and some other organs. The study is conducted on pieces of organ tissue that are taken with a special method called a biopsy.