Violation of lipid metabolism
Lipids - Fats and Lipids is a large group of substances that includes a large number of different substances, for example triglycerides, cholesterol, cholesterol esters, free fatty acids, phospholipids, sphingolipids. The general physicochemical property of most lipids is poor solubility in water. In this regard, their movement in the body is possible only in the form of complex compounds with proteins or in the presence of bile acids. Lipids are the most important constituent of all cells of the body and are part of the cell membranes. Significant amounts of lipids are concentrated in the brain, subcutaneous fat layer, and periphytal fatty tissue. They have low thermal conductivity, perform the function of an insulator, which protects the body from cooling. The presence of lipids is necessary for the delivery of fat-soluble vitamins - A, D, E, K, to the body. Fatty acids are the most important source of energy, through which up to 50% of the daily energy requirement can be provided.
Splitting and absorption of lipids mainly occurs in the small intestine. The time of their digestion does not exceed 20 minutes. At the same time, approximately 25-45% of the fat ingested in the body with food is completely cleaved. Under the influence of the pancreatic enzyme, which breaks down lipids( lipase), a mixture is formed in the intestine, consisting of various lipids and fatty acids. Phospholipids( fat molecules containing phosphorus) before being absorbed in the intestine also undergo cleavage. In children of the first year of life who are breastfed, mother's milk plays a major role in the processes of lipid digestion, since it contains an enzyme that breaks down these compounds( lipase).
The most intense absorption of fat from food is in the initial parts of the small intestine, while in the more remote areas, along with absorption, fat release also occurs. In this regard, when limiting fat in the diet, it is allocated slightly more than is contained in food. The size of fat particles is very important for fat absorption. With a lack of pancreatic enzymes, fat absorption with a small molecule size can be undisturbed, while larger particles are almost not absorbed. The transition of fat to a state in which it can be absorbed in the intestine( emulsification of fat - passes into a state of emulsion) is promoted by bile acids. These acids form a complex with fats that are highly soluble in water, which ensures their absorption. Disturbance of fat absorption is observed in excess of calcium and magnesium salts in food. Some antibiotics interfere with the cleavage of lipids and thus increase its excretion with feces( steatorrhea).Absorption of fat is also disturbed by inflammatory processes in the intestine, intoxication, with a deficiency of vitamins A and B complex, with adrenal diseases.
In recent years, much attention is paid to the role of fatty acids in the body - linoleic, linolenic, arachidonic. These acids, except for arachidonic, come only with food. In the case of a lack of these substances, all kinds of violations of the functions of many organs and systems develop. In an animal experiment, it was found that when eating food that does not contain unsaturated fatty acids, the growth of young animals was delayed. In addition, skin flaking, hair loss, subcutaneous hemorrhage, increased fluid and oxygen consumption, decreased urine production, protein appeared in the urine and red blood cells( red blood cells) appeared. Similar violations of health in the deficit of these same fatty acids were noted in children. In the latter case, the deficit of fatty acids was manifested by growth retardation, a decrease in the body's resistance to various infections, and changes in the skin. All manifestations of deficiency disappear in the event that at least 2% of caloric needs of the child are provided by linoleic acid. All of the above facts have allowed to combine such fatty acids into one group - the vitamins of group F. Significant amounts of these acids are contained in vegetable oils, which explains the need to include these products in the diet of children, both breastfed and older. It was found that arachidonic acid does not enter the human body with food, but only is synthesized in it, and it is also formed from fatty acid - linolenic acid. A significant influence on the metabolism of fatty acids is provided by vitamin B6( pyridoxine).
Compounds such as triglycerides perform mainly functions of reserve compounds in the human body, from which fatty acids are formed, if necessary. Since the latter are the material from which the organism, as a result of numerous chemical transformations, receives energy, they are formed from triglycerides only when the body's need for energy material is increased. In fact, they perform the same function that glycogen performs, being a reserve compound of carbohydrates.
The importance of a lipid, like cholesterol, lies, on the one hand, in that it is part of a number of organs and tissues, providing them with a normal chemical structure, and on the other, is the precursor of many compounds of the steroid series. Steroid compounds include hormones of the adrenal cortex( corticosteroids) and sex hormones, as well as vitamin D and bile acids. The greatest amount of cholesterol in a healthy person is found in the adrenal glands, in the brain and in nervous tissue. In smaller amounts, it is found in the liver, bone marrow, adipose tissue and blood. Part of the cholesterol is in the body in a free state, the other - in the form of compounds with fatty acids( esters).The ratio of free and bound cholesterol in blood plasma is relatively constant and is 1: 3, respectively. With liver damage, the proportion of bound cholesterol is significantly reduced. Cholesterol not only enters the human body with food, but it can also form in it from other compounds. Cholesterol decay occurs mainly in the liver. As a result, bile acids are formed, which are secreted with bile. The bile enters the intestine, and along with it, there is a large amount of cholesterol, which is reabsorbed in the duodenum and the initial sections of the small intestine. In this case, cholesterol can in some quantities be removed from the large intestine.
Phospholipids are substances that are a fat that contains a certain amount of phosphorus. Such compounds are capable of dissolving both in organic solvents and in water. Phospholipids are part of the cell membrane, play an essential role in the processes of blood clotting. They are divided into several groups, one of which are sphingolipids, which play a big role in the processes of formation of a membrane covering the nerve fibers in the body of a healthy person( myelin sheath).Since such an amino acid as tyrosine takes part in the construction of such a cladding, its deficiency in phenylketonuria can also lead to significant disorders from the nervous system.
Before 6 months of life, the content of myelin in the brain is still low, but it increases rapidly after this period, and by three years of life the chemical structure of the brain tissue corresponds to that of adults.
The human brain is composed of gray and white matter. The cerebral cortex is made up of gray matter, and the rest of the tissue is made of white matter. In this case, white matter contains three times more cholesterol and other lipids than the cortex of the brain. The water content in the brain during the formation is 90%, and in the process of maturation decreases, reaching 75% in the mature brain. The fetal brain absorbs a small amount of oxygen, but it sharply increases at the 2-6 month of life. This explains the relative stability of the brain of the newborn to oxygen deficiency( hypoxia).
To determine the various lipid metabolism disorders of , modern biochemical methods of research are of great importance, in which it is possible to determine the content of total lipids, cholesterol, and phospholipids in the body.
It is currently accepted to distinguish 3 main types of hereditary disorders of fat metabolism:
1) diseases with predominantly elevated blood lipid levels, or plasma lipoids;
2) diseases characterized by accumulation of lipids inside cells, - intracellular lipoids;
3) the disease of the exchange of lipoproteins( complex lipid compounds with proteins).