Acid-Base Regulation

The acid-base balance is closely coupled to the fluid metabolism and electrolyte metabolism and disorders of one system and the other system is often compromised.

Metabolic processes continuously produce acid and to a lesser extent bases. The Hydron + H is in this case especially reactive; it can bind to negatively charged proteins and change their total charge, structure and function in high concentrations. In order to maintain cell functions, the body has complex mechanisms that keep the H + concentration in the blood within a narrow range – typically 37-43 nmol / l (pH 7.43-7.37, and pH = -log [H + ]) and ideally at 40 nmol / l (pH = 7.40). Disturbances of these regulatory mechanisms can have serious clinical consequences. The acid-base balance is closely coupled to the fluid metabolism and electrolyte metabolism and disorders of one system and the other system is often compromised. Acid-base physiology Most acids come from carbohydrate and fat metabolism of carbohydrate and lipid metabolism generate daily between 15,000 and 20,000 mmol carbon dioxide (CO2). CO2 per se is not an acid, but in the presence of the enzymes, which are counted to the carbonic anhydrase, is CO2 connects in the blood with water (H2O), whereby carbonic acid is formed (H2CO3) extending (in hydrogen ion (H +) and bicarbonate HCO3 -) separates. The H + binds to the hemoglobin in the red blood cells and is released in the course of oxygenation in the alveoli, which takes place by a different carbonic anhydrase a reverse of the previous reaction. In this case the water formed (H2O) that is excreted by the kidneys, and carbon (CO2), which is exhaled during each breath. Minor amounts of organic acid incur the following reasons: Incomplete metabolism of glucose and fatty acids in lactic acid and keto acids metabolism of sulfur-containing amino acids (cysteine, methionine) to sulfuric acid metabolism of cationic amino acids (arginine, lysine) hydrolysis of ingested through the diet phosphate These “fixed “or” metabolic “acid load can not exhaled and therefore must be neutralized or excreted by the kidneys. Most bases derived from the metabolism of anionic amino acids (glutamate and aspartate) and from oxidation and consumption of organic anions such as lactate and citrate, resulting in the formation of HCO3-. Acid-base balance The acid-base balance is maintained by chemical buffering and by pulmonary and renal activity. Dry chemical buffering buffers are solutions that resist changes in pH. Intra- and extracellular buffers may react directly to an acid-base imbalance. Bone also play an important role in buffering, especially in acid loads. A buffer composed of a weak acid and its conjugate base. The conjugate base can bind H + and the weak acid may be proposed, whereby changes in the free H + concentration can be minimized. A buffer system minimizes changes in pH best near its equilibrium constant (pK). Therefore, even though there may be many pairs of buffers in the body, some physiologically relevant. The relationship between the pH of a buffer system and the concentration of its components is described by the Henderson-Hasselbalch equation: where pKa is the dissociation constant of the weak acid is a clinical computer Henderson-Hasselbach equation, the major extracellular buffer is the HCO3- / CO2System which is described by the following equation: an increase in H + concentration shifts the equation to the right and generate CO2. This important buffer system is highly regulated. The CO2 concentrations may be precisely controlled by the alveolar ventilation, while H + and HCO3 – concentrations can be regulated precisely by renal excretion. The relationship described by the Henderson-Hasselbalch equation between pH, HCO3- and CO2 in the system is therefore: Similarly, the relationship is described by the cashier bleaching equation which was derived from the Henderson-Hasselbalch equation: Note : to convert the arterial pH in [H +], use: or show both equations that the acid-base balance is based on the ratio between PCO2 and HCO3- and not on the absolute value of only one of the two alone , With these formulas any two of the variables can be used to calculate the third. Other important physiological buffers are intracellular organic and inorganic phosphates, and proteins, including the Hb in the erythrocytes. Less important are extracellular phosphate and plasma proteins. are bones become an important buffer as soon as an acid load caused by the intake of food. Bone initially put sodium bicarbonate (NaHCO3) and calcium hydrogen carbonate (Ca (HCO 3) 2) in exchange for H + free. With prolonged acid exposure bone calcium carbonate (CaCO3) and calcium phosphate liberate (CaPO4). Therefore, a continuing acidemia contributes to bone demineralization and osteoporosis bei.Pulmonale regulation of the CO2 concentration is determined by changes in tidal volume and respiratory rate (minute volume) accurately regulated. A pH drop is registered by arterial and chemoreceptors leads to an increase in tidal volume or respiratory rate; CO2 is exhaled and the pH value in the blood increases. In contrast to the immediate onset of chemical buffering respiratory regulation needs minutes to hours. It has an efficiency of 50-75%, but is not able to completely normalisieren.Renale regulation The kidneys control the pH-value by the regulation of the amount of HCO3-, which is secreted or reabsorbed pH. The reabsorption of HCO3- is equivalent to the excretion of free H +. Changes in renal done acid-base processing hours to days after the onset of the changes in the acid-base balance. The complete HCO3- in the serum is filtered while it is being transported through the glomerulus. The HCO3 – reabsorption in the proximal tubule and is usually carried out to a lesser extent in the headers. The H2O in the cells of the distal tubules splits into H +, and hydroxide (OH-). In the presence of carbonic anhydrase, the OH- combines with CO2 and HCO3- form that is transported back to the peritubular capillaries, while the H + is secreted into the tubule lumen, and reacts with free filtered HCO3- to CO2 and H2O, which are well reabsorbed. In this way, distal reabsorbed HCO3 – ions are newly formed and are not identical with the previously filtered ions. A decrease of the effective circulation volume (. Such as with diuretics) increases HCO3 – reabsorption, while an increase of parathyroid hormone in response to an acid load that HCO3 – reduces reabsorption. Likewise, an increase in PCO2 leads to increased HCO 3 – reabsorption, while a reduction of chloride (Cl) (usually by volume depletion) to an increased sodium (Na +) – reabsorption and increased HCO3 – production in the proximal tubule leads. Acid is actively secreted in the proximal and distal tubules, where it binds to Harnpuffer – free filtered primarily phosphate (HPO4-2), creatinine, uric acid and ammonia – to be transported from the body. The ammonia buffer system is particularly important, since the other buffers are filtered in defined concentrations and can be exhausted at a high acid load; in contrast, the tubule cells actively control ammonia at changes in the acid load. Arterial pH is the major determinant of the acid precipitation but the precipitation is also controlled by the potassium (K +), Cl- and aldosterone levels. The intracellular K + concentration and H + secretion are reciprocally interdependent; K + losses cause increased H + secretion and thus a metabolic alkalosis.

Health Life Media Team

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