26.5 Renal Regulation

Lungs eliminate ——

volatile carbonic acid by eliminating CO₂

kidneys eliminate

• nonvolatile (fixed) acids produced by cellular metabolism (phosphoric, uric, and lactic acids and ketones) to prevent metabolic acidosis

kidneys regulate alkaline substances; and renew them

Kidneys regulate acid-base balance by adjusting amount of bicarbonate in blood by either:

• Conserving (reabsorbing) or generating new HCO₃^–

• Excreting HCO₃^–

To maintain alkaline reserve

kidneys must replenish (reabsorb) bicarbonate

When body is in alkalosis, type B intercalated cells can:

• Secrete HCO₃^–

• Reclaim H⁺ to acidify blood

Even during alkalosis, nephrons and collecting ducts conserve more

HCO₃^– than they excrete