BLOOD BUFFER SYSTEMS (LECTURE)

Abstract

This lecture is devoted to theoretical foundations of blood buffer systems functioning. Biochemical aspects and physiological activity of phosphate, hydrogen carbonate buffer and its combined activity with hemoglobin buffer, which ensures stability of blood pH, are presented. Chemical reactions to achieve the required blood pH are investigated. The combination of buffer properties, one of the components of which is CO₂ gas and autonomous self-regulation by intracellular hemoglobin ensures the blood plasma pH constancy. Stabilizing systems are considered - the respiratory apparatus and kidneys, which create the possibility of maintaining the stability of extracellular fluid pH. Respiratory acidosis, alkalosis, metabolic acidosis are considered on the biochemical level. This article presents information about hemoglobin structure: heme structure and globin subunits in different types of hemoglobin. The following mechanisms which provide maximum oxygen saturation of lungs and maximum oxygen emission in the tissues: heme-hemic interaction, Bohr effect and influence of 2,3-diphospho-glycerate connected with haemoglobin, are considered. The protein buffer system has been characterized in the in general. The capacity of the phosphate buffer system has been shown to be close to 1-2% of the whole buffer capacity of the blood and up to 50% of the buffer capacity of urine. The organic phosphates also exhibit buffering activity in the cell. Human and animal organisms can have intracellular pH from 4.5 to 8.5 depending on the type of cells, but the blood pH should be 7.4. This parameter is ensured by the hydrogen carbonate buffer system. Moreover, the blood pH depends not on the absolute concentrations of buffer components but on their ratio. The most powerful is hemoglobin buffer system that accounts for 75% of the whole blood buffer system. For stabilization of buffer capacity, the body uses two other stabilizing systems - the respiratory apparatus and kidneys. At the same time, the compensatory role of the respiratory system has shortcomings. Hyperventilation of lungs causes respiratory alkalosis.  Hypoventilation has a counteracting effect by lowering the pH of the blood. Thus, the blood buffer system is ensured by a complex system that allows the organisms to adapt to changes in the fluid medium and regulate the pH under pathological conditions.