at basolateral side into blood 9 HCO 3 – + H + from tubule H 2 CO 3 10 At brushborder, H 2 CO 3 H 2 O + CO 2 again; Carbonic Anhydrase catalyzes CO 2 enters t. cell and H 2 O passes out in urine - thereby, excreting the H + that was originally in blood! CO 2 diffuses from blood into t. cell PLUS CO 2 from Aerobic Respiration 11 Glomerular filtrate H + H CO 3 H + H 2 O H + H 2 O peritubular capillary Renal tubule cells proximal convoluted tubule Tubular fluid Carbonic Anhydrase Caveats : 1.Step #6 : If tubular fluid H + conc. increases (to pH of 4.5), H + secretion stops; limits Na+/H+ exchange. 2. The more acid (H+) the kidneys secrete, the less Na+ remains the urine.
24-63 Acid Buffering in the Urine Diffuses thru channel Antiport Key Tubular fluid K + Na + +Na H 2 PO 4 Na + Na + Urine HCO 3 – + HCO 3 – HCO 3 – N H 4 Cl + Glomerular filtrate NH 3 H 2 CO 3 H + Amino acid catabolism H + H 2 CO 3 Diffusion thru membrane H + + NH 3 + Cl – H + + Na 2 HPO 4 peritubular capillary Renal tubule cells proximal convoluted tubule Diffusion thru channel
24-64 Disorders of Acid–Base Balance two categories, Respiratory and Metabolic Respiratory acidosis, occurs when .. . * Ventilation rate fails to keep pace with CO 2 production * CO 2 accumulates in the ECF pH * Emphysema with severe reduction of functional alveoli Respiratory alkalosis, occurs when .. . * Hyperventilation * CO 2 eliminated faster than CO 2 produced Metabolic acidosis, occurs when .. . * organic acid production, e.g., lactic acid, ketone bodies (DM) * Ingestion of acidic drugs, e.g., aspirin * Loss of base, e.g. , chronic diarrhea, laxative overuse Metabolic alkalosis, rare but occurs when .. . * Overuse of bicarbonate , e.g., antacids, IV bicarbonate solutions * Loss of stomach acid, e.g., chronic vomiting
24-65 Compensation for Acid–Base Imbalances Compensated acidosis or alkalosis Either the kidneys compensate for pH imbalances of respiratory origin, or the respiratory system compensates for pH imbalances of metabolic origin Uncompensated acidosis or alkalosis A pH imbalance the body cannot correct without clinical intervention
24-66 Compensation for Acid–Base Imbalances Respiratory Compensation - fast, best for short term pH imbalance * changes in pulmonary ventilation to correct pH of body fluids by expelling or retaining CO 2 Hypercapnia , excess CO 2 stimulates ventilation, eliminating CO 2 pH Hypocapnia , CO 2 deficiency ventilation reduced, allowing CO 2 to accumulate pH
24-67 Compensation for Acid–Base Imbalances Renal compensation , alter rate of H + secretion pH Slow , but better at fully restoring pH than lungs Kidneys effectively compensate for pH imbalances that last a few days or longer. In Acidosis, urine pH may drop to 4.5 due to excess H + increased rate of H + secretion ( and NH 3 to buffer H + ) pH in the body In Alkalosis, urine pH as high as 8.2 due to excess HCO 3− decreased rate of H + secretion and neutralization of bicarbonate, pH in the body Note: Kidneys cannot act fast enough to compensate for short-term pH imbalances
24-68 Good review/reference/self-quiz tool
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