Hydrogen ions excretion

Mechanism of Action A mineralocorticoid that acts at distal tubules. Therapeutic Effect Increases potassium and hydrogen ion excretion. Replaces sodium loss and raises blood pressure (with low dosages). Inhibits endogenous adrenal cortical secretion, thymicactivity, and secretion ot corticotropin by pituitary gland (wit h higher dosages). 

Acts on the distal tubules to increase potassium excretion, hydrogen ion excretion, and sodium reabsorption and subsequent water retention... 

Prolonged bed rest is associated with increased urinary nitrogen excretion. Calcium, sodium, potassium, phosphate, and sulfate excretions are increased hydrogen ion excretion is reduced, presumably caused by decreased metabolism of skeletal muscle. The amplitude of circadian variation of plasma cortisol is reduced by prolonged immobilization, and the urinary excretion of catecholamines may be reduced to one third of the concentration in an active individual. Vanil-lylmandehc acid excretion is reduced by one fourth after 2 to 3 weeks of bed rest. 

The proximal tubule is the most metabolically active part of the nephron, facilitating the reabsorption of 60% to 80% of the glomerular filtrate volume—including 70% of the filtered load of sodium and chloride, most of the potassium, glucose, bicarbonate, phosphate, and sulfate—and secreting 90% of the hydrogen ion excreted by the kidney (Table 45-1). 

Figure 46-11 Hydrogen ion excretion, sodium hydrogen ion exchange, and ammonia production in the renal tubules. Key I, conversion of HPO to HiPO 2, reaction of hydrogen ions with NH3 3, excretion of undissociated acids 4, Na -H exchange 5, NH3 production and 6, synthesis of carbonic acid from CO2.

Administer oxygen to improve tissue perfusion and decrease metabolic acidosis Administer oxygen to decrease respiratory acidosis Increase the respiratory rate to treat respiratory acidosis Decrease the respiratory rate to treat respiratory acidosis Administer medicines to decrease renal hydrogen ion excretion... 

The sulfonamide carbonic anhydrase inhibitors, such as sulfanilamide, acet-azolamide, and their congeners, have contributed significantly to the knowledge of renal function—e.g., the site and origin of the hydrogen ion excretion and the site of potassium ion excretion. 

Chronic respiratory acidosis is usually a long-standing condition, and isaccompanied by maximal renal compensation. In a chronic respiratory acidosis the primary problem again is usually impaired alveolar ventilation, but renal compensation contributes markedly to the acid-base picture. Compensation may be partial or complete. The kidney increases hydrogen ion excretion and ECF bicarbonate levels rise. BUwtd [ll tends back towards normal (Fig., 1). 

B. Effects All three drugs in this class cause an increase in sodium clearance and a decrease in potassium and hydrogen ion excretion and therefore qualify as potassium-sparing diuretics. They may cause hyperkalemic metabolic acidosis (Table 15-2). 

The adrenal cortex secretes a potent mineraiocorticoid called aldosterone, which promotes salt and water retention and potassium and hydrogen ion excretion. 

The kidneys influence blood pH by varying the amount of hydrogen ions excreted in the urine. When the blood is too acidic, carbonic acid is converted to bicarbonate ions and hydrogen ions. The hydrogen ions are excreted, and the bicarbonate ions enter the blood. 

Wrong, O. Urinary hydrogen ion excretion in patients with uric acid calculi. Proceed. Royal Soc. Med. 59 27-34 (1966). 

Reabsorption of most of the bicarbonate is coupled with hydrogen ion excretion. Thus, when NaHC03 is filtered, the salt is dissociated in the urine to Na and HCO3. The sodium is reabsorbed, and in the presence of ions, which are generated in the tubular cells, HCO3 and carbonic anhydrase, found at the surface of the tubular cells, yield CO2 and H2O. 

Cleland RE (1975) Auxin-induced hydrogen ion excretion correlation with growth, and control by external pH and water stress. Planta 127 233-242 Cleland RE (1976) Kinetics of hormone-induced H excretion. Plant Physiol 58 210-213 Cleland RE, Prins H, Harper R, Higinbotham N (1977) Rapid hormone-induced hyperpolarization of the oat coleoptile transmembrane potential. Plant Physiol 59 395-397 Clor MA (1967) Translocation of tritium-labelled gibberellic acid in pea stem segments and potato tuber cylinders. Nature 214 1263-1264 Cohen D, Robinson JB, Paleg LG (1966) Decapitated peas and diffusible gibberellins. Aust J Biol Sci 19 535-543... 

There was impaired renal tubular concentrating function within 2 years of therapy with adefovir in 11 recipients of kidney transplants with chronic hepatitis B virus infection [8 ]. There was a significant rise in serum creatinine from 125 to 141 pmol/l and a significant increase in 24-hour proteinuria. Urinary pH fell from 6.60 to 5.65 and bicar-bonaturia from 0.33 to 0.10 mmol/hour. Urinary hydrogen ion excretion rose from 1.79 to 2.44 mmol/1 and there were significant falls in phosphatemia, phosphaturia threshold, and tubular phosphorus reabsorption the phosphorus index of excretion rose. 

The balance shown in Figure 3.5C is disturbed when the extracellular hydrogen ion concentration changes. If this falls, the renal compensation involves a reduction in bicarbonate reabsorption and a reduction in hydrogen ion excretion (Figure 3.5C). These changes in composition of the urine result in the production of an alkaline urine as part of the physiological response to... 

For each hydrogen ion excreted, one bicarbonate ion is added to the intracellular fluid of the renal tubular cell. The intracellular concentration of bicarbonate rises. In Figure 7.1 B, the reaction of CO2 is omitted and only the products Fl and HCO, are reproduced from Figure 7.1 A. Bicarbonate, being charged, is insoluble in lipid and so diffuses extremely slowly across the lipid regions of the cell membrane. On the aspect of the tubular cell membrane facing the interstitial fluid, the lipid membrane is traversed by protein macromolecules which comprise a carrier mechanism for bicarbonate ions (section A.l). The rise in intracellular concentration of bicarbonate leads to transfer of bicarbonate from the renal tubular cell cytoplasm to the renal interstitial fluid. 

There is a limit to the magnitude of the gradient against which pumping can occur this limit is reached when the pH of the tubular fluid falls to around 4.5. If all the hydrogen ions excreted from the body via the urine were freely ionized in the urine, the amount of acid which could be excreted would be limited to the amount present in solution with a pH of 4.5 and this is. 10 micromoles of hydrogen ions per litre of urine. If in 24 hours Ij litres of urine is excreted, this corresponds to a total daily excretion of 45 micromoles of hydrogen ions. Metabolism in a person on a typical omnivorous diet yields... 

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