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An organism can be defined as a physico-chemical system existing in the environment in a stationary state. To ensure a stationary state, all organisms have developed various anatomical, physiological and behavioral devices that serve the same purpose - to maintain the constancy of the internal environment. This relative dynamic constancy of the internal environment (blood, lymph, tissue fluid) and stability of the basic physiological functions of the human and animal body is called homeostasis. This process is mainly carried out by the activity of the lungs and kidneys due to the respiratory and excretory functions. Homeostasis is based on maintaining the acid-base balance. For the normal functioning of most cells, fairly narrow pH limits (6.9 - 7.8) are necessary, and the body is forced to constantly neutralize the formed acids. This process is carried out by buffer systems that bind excess hydrogen ions and control their further movement in the body. Buffer systems play a very important role, because as a result of various metabolic processes in the body, various acids are constantly formed, which are immediately neutralized by buffer systems: hydrocarbonate, phosphate, protein and hemoglobin. The main buffer system of the body is a hydrocarbonate buffer consisting of H2СО3 and NaHCO3. At a pH of about 7.4, the hydrogen carbonate ion prevails in the body, and its concentration can be 20 times higher than the concentration of carbonic acid. By its nature, carbonic acid is very unstable and immediately after its formation it splits into carbon dioxide and water. Reactions of formation and subsequent rapid decomposition of carbonic acid in the body are so perfect that they are often not given special importance. These reactions are catalyzed by the enzyme carbonic anhydrase, which is located in erythrocytes and in the kidneys. The peculiarity of the hydrocarbon buffer system is that it is open. An excess of hydrogen ions binds to a hydrogen carbonate ion, the carbon dioxide formed thereby stimulates the respiratory center, the ventilation of the lungs increases, and excess carbon dioxide is removed during breathing. This is how the pH balance is maintained in the body. The more hydrogen ions are formed in the cells, the greater the buffer consumption. At this stage, the kidneys are connected to the metabolism, which remove excess hydrogen ions, and the amount of bicarbonate in the body is restored. Phosphate buffer can act both as part of organic molecules and as free ions. One of its molecules is capable of binding up to three hydrogen cations. Proteins can attach both acidic and basic groups to their polypeptide chain. The buffer capacity of the protein buffer system can cover a wide range of pH. Depending on the available pH, it can bind both hydroxyl groups and hydrogen ions. The third part of the buffer capacity of blood is accounted for by hemoglobin. Each hemoglobin molecule can neutralize several hydrogen ions. When oxygen passes from hemoglobin to tissue, the ability of hemoglobin to bind ions to hydrogen increases and vice versa: when oxygenation of hemoglobin occurs in the lungs, it loses hydrogen ions. Released hydrogen ions react with hydrogen carbonate, and as a result, carbon dioxide and water are formed. The formed carbon dioxide is removed from the lungs during breathing. Buffer properties of hemoglobin are determined by the ratio of reduced hemoglobin (Hb) and its potassium salt (KHb). In weakly alkaline solutions, such as blood, hemoglobin and oxyhemoglobin have properties of acids and are donors of H+ or K+. This system can function independently, but in the body it is closely connected with the hydrocarbon system. When the blood is in the tissue capillaries, where acidic products come from, hemoglobin performs the functions of a base: КНb + Н2СО3 ↔ ННb + КНСО3. In the lungs, hemoglobin, on the contrary, behaves like an acid, preventing blood alkalinization after the release of carbon dioxide. Amino acid and protein buffer systems. The buffering effect of these buffer systems begins to manifest when adding a certain amount of acid or alkali to them. A mixture of two forms of protein is formed: a) weak "protein-acid" + salt of this weak acid b) weak "protein-base" + salt of this weak base жүктеу/скачать 119,35 Kb. Достарыңызбен бөлісу:
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