What effect does hyperventilation have on HCO3– recovery in the kidneys?

a. Less H+ excretion, greater HCO3– loss
b. No effect as these involve two independ-ent systems.
c. Vicious cycle of worsening alkalemia as hyperventilation stimulates increased HCO3– retention.
d. Escalating retention of other buffer bases along with HCO3–.

ANS: A
If blood CO2 is low, as is the case in a state of hyperventilation (see Figure 14-3), the ratio of HCO3– ions to dissolved CO2 molecules increases. Consequently, the renal filtrate has more HCO3– ions than H+ ions. Because HCO3– cannot be reabsorbed without first reacting with H+, the excess HCO3– ions are excreted in the urine, carrying with them positive ions in the filtrate such as Na+ or K+. Therefore, the net effect of secreting fewer H+ ions is to increase the quantity of HCO3– (base) lost in the urine.