Acid-base balance control

Rainwater and snowmelt water are primary factors determining the very nature of the terrestrial carbon cycle, with photosynthesis acting as the primary exchange mechanism from the atmosphere. Bicarbonate is the most prevalent ion in natural surface waters (rivers and lakes), which are extremely important in the carbon cycle, accoxmting for 90% of the carbon flux between the land surface and oceans (Holmen, Chapter 11). In addition, bicarbonate is a major component of soil water and a contributor to its natural acid-base balance. The carbonate equilibrium controls the pH of most natural waters, and high concentrations of bicarbonate provide a pH buffer in many systems. Other acid-base reactions (discussed in Chapter 16), particularly in the atmosphere, also influence pH (in both natural and polluted systems) but are generally less important than the carbonate system on a global basis. 

Carbonate anhydrase (carbonic anhydrase, EC 4.2.1.1) catalyzes the reversible interconversion of C02 and HCO3 (see Sect. 3.7.3). The enzyme is found in erythrocytes, and in kidney and gastric juices where it contributes to the control of the acid-base balance. The esterase activity of carbonic anhydrase is probably due to the similarity between its active site and that of the zinc proteases. A possible physiological role of the esterase activity of this enzyme remains to be established. 

Homeostasis. The blood ensures that a balanced distribution of water is maintained between the vascular system, the cells (intracellular space), and the extracellular space. The acid-base balance is regulated by the blood in combination with the lungs, liver, and kidneys (see p. 288). The regulation of body temperature also depends on the controlled transport of heat by the blood. 

The kidneys main function is excretion of water and water-soluble substances (1). This is closely associated with their role in regulating the body s electrolyte and acid-base balance (homeostasis, 2 see pp.326 and 328). Both excretion and homeostasis are subject to hormonal control. The kidneys are also involved in synthesizing several hormones (3 see p. 315). Finally, the kidneys also play a role in the intermediary metabolism (4), particularly in amino acid degradation and gluconeo-genesis (see p. 154). 

Metabolic or respiratory acidosis Cautiously institute amiloride in severely ill patients in whom respiratory or metabolic acidosis may occur, such as patients with cardiopulmonary disease or poorly controlled diabetes. Monitor acid-base balance frequently. Shifts in acid-base balance alter the ratio of extracellular/intracellular potassium the development of acidosis may be associated with rapid increases in serum potassium. 

Mecftanism of Action Sodium Is a major cat ion of extracellular fluid that controls water distribution, fluid and electrolyte balance, and osmotic pressure of body fluids it also maintains acid-base balance. 

The kidney regulates the acid-base balance of the body by control over resorption of sodium ions, which may exchange for hydrogen ions in the kidney tubule. Since most dietaries are of acid-ash, the urine is usually more acid than the original plasma filtrate and much of the phosphate excreted is thus changed to the acid monosodium salt, Within the range of normal variability, with an alkaline ash diet, the urine may become alkaline, and in extreme instances, some sodium bicarbonate may be excreted. 

SODIUM The most abundant extracellular cation (positive ion). It influences the degree of water retention in the body and is an important participani in the control of acid-base balance. 

In 18 children with nalidixic acid intoxication, most of whom were aged under 1 year, the clinical effects were neurological disorders of alertness, hjrpertensive cranial syndrome, and neuronal damage some had a metabolic acidosis (30). Treatment included gastric lavage, correction of acid-base balance, and control of convulsions. 

T he sea is a living system and, like other living systems, its properties are a complex fimction of many chemical and biological processes. Some of these involve, directly or indirectly, the protonation of basic species, and consequently the state of the seawater system— its equilibrium processes and the rate at which equilibrium is being approached —depends on pH. Interactions within the hydrosphere, in which carbonate, phosphate, and silicate play an important role, regulate the pH within rather narrow limits, as the acid-base balance of the human body controls the pH of human blood. 

The kidney is an organ that performs several important functions essential to sustain life. These functions include the regulation of volume and electrolyte homeostasis, control of acid-base balance, and the excretion of waste products. The kidney also has endocrine functions including renin secretion, stimulation of erythropoietin formation, and activation of vitamin D. Numerous disease states (e.g., infections, shock, diabetes, gout) can affect the ability of the kidney to perform its normal functions, and if these diseases are not properly treated, serious illness or death can result. 

Inhibitors to the enzyme carbonic anhydrase. This enzyme is widely distributed in the body and has a fundamental role in the control of acid-base balance. In the 1920s it was noticed that the SULPHONAMIDE sulfanilamide had a weak diuretic action. Acetazolamide is a subsequent thiadiazole-sulphonamide derivative with potent carbonic anhydrase inhibitor activity. Clinically, it is used for antiglaucoma TREATMENT, is a weak diuretic and can be used to treat mountain sickness. Dichlorphenamide and dorzolamide are sulphonamide derivatives also used for antiglaucoma treatment. Methazolamide is used as a diuretic. Now that seven or more isoenzymes of carbonic anhydrase have been cloned. Isolated and mapped, some new initiatives are aimed at developing agents with more selective actions. 

The kidneys are critical organs. They filter wastes produced by metabolism from the blood and excrete them with water as urine. They are also major organs in whole body homeostasis, with acid-base balance, electrolyte concentration regulation, blood volume control, and blood pressure regulation functions. 

Control of acid-base balance. Production of lactate in excess of its clearance causes metabolic acidosis, and resynthesis of glucose from lactate is a major... 

I Increased sensitivity to inhaled CO2 in panic disorder leading to panic anxiety (but paradoxically voluntary hyperventilation, causing hypocapnia, can also induce panic). I Lactate infusion (possibly by altering acid-base balance) provokes panic in attxious patients but not in controls. 

I. Acid Base Balance. Trauma from whatever cause may strain control of the acid-base balance by increasing production of acids, especially where there is tissue anoxia, by diminishing power of lungs and kidneys to eliminate them, and by lowering of buffering capacity through anemia and hypoproteinemia [for review, see Walker (W2)]. 

Respiratory alkalosis is much less common than acidosis but can occur when respiration is stimulated or is no longer subjcci to feedback control (Fig. 4). Usually these are acute conditions, and there is no renal compensation. The treatment is to inhibit or remove the cause of the hyperventilation, and the acid-base balance should return to normal. Examples are ... 

Mechanisms of Respiratory Control. To meet the metabolic demands of the body and to maintain the acid-base balance, ventilation is regulated by various stimuli acting at several locations in the body. Although the mechanism by which each stimulus acts in amplifying or diminishing ventilation is not well known, these stimuli clearly inhibit and excite the central respiratory centers in the medulla, either directly or indirectly. The electrical impulses generated in these centers are responsible for the motor activities which produce the ventilatory response. 

Phosphorus has more known functions in the animal body than any other mineral element. Together with calcium, phosphorus plays a major role in the formation of bones and teeth, as well as eggshells. It is a component of nucleic acids, which control cell multiplication, growth and differentiation. In combination with other elements, phosphorus has a role in the maintenance of cellular osmotic pressure and the acid-base balance. Energy transfer processes in all living cells involve interconversion of the phosphate-containing nucleotides, adenosine diphosphate (ADP) and ATP, and thus phosphorus participates in all biological events. Other roles include its presence in phospholipids, where it functions in cell-wall structure, fatty acid transport and protein as well as amino acid formation. 

The bicarbonate ion (HCO3A is the second-largest anionic contributor to maintaining acid-base balance, and its secretion from the pancreas helps to neutralize the contents of the small intestine. Respiration controlling the carbon dioxide concentration of the blood (PaCOj) and renal excretion of bicarbonate are the two main homeostatic influences on plasma bicarbonate. Within the renal tubular lumen, carbonic anhydrase converts carbonic acid into carbon dioxide, which diffuses into the epithelial cells and forms carbonic acid, which later dissociates to bicarbonate. 

After urea is formed, it diffuses out of liver cells into the blood, the kidneys filter it out, and it is excreted in the urine. Normal urine from an adult usually contains about 25-30 g of urea daily, although the exact amount varies with the protein content of the diet. The direct excretion of NH4 accounts for a small but important amount of total urinary nitrogen. Ammonium ions can be excreted along with acidic ions, a mechanism that helps the kidneys control the acid-base balance of body fluids. 

Buffer—An acid-base balancing or control reaction in which the pH of a solution is protected from major change when acids or bases are added to it. 

Acid-base balance is critical to homeostasis. The pH, a measure of the acidity and alkalinity of a solution, in the body can determine if a required or desired reaction will occur and the effectiveness of that reaction. The enzymes that control the reactions that occur in the body operate under very specific environmental conditions involving temperature and narrow ranges of pH. Metabolism affects and is affected by the pH of body fluids. While the average range of pH in arterial blood lies between 7.35 and 7.45, the blood pH that is compatible with life in mammals is limited to a range between 6.8 and 7.8. If the pH of arterial blood is outside this range, irreversible cell damage can occur. 

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