What effect does hyperventilation have on HCO3 recovery in the ...

[sammy]

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.

Question 2

What is the role of carbonic anhydrase in the kidneys?
 
  a. It drives the recovery of HCO3 and ex-cretion of H+.
  b. It is the catalyst for the hamburger phe-nomenon.
  c. It promotes the excretion of CO2 in the urine.
  d. It promotes the loss of fluids in congestive heart failure.

[AISCAMPING]

Answer to Question 1

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.

Answer to Question 2

ANS: A
The HCO3 ions in the filtrate react with the H+ ions secreted by the tubular cells. The resulting carbonic acid breaks down into CO2 and water. Because CO2 is extremely diffusible through bi-ological membranes, it diffuses instantly into the tubule cell. There, CO2 reacts rapidly with water in the presence of carbonic anhydrase, rapidly forming HCO3 and H+. The HCO3 ion diffuses back into the blood. Thus, the reabsorbed HCO3 ion is not the same HCO3 ion that existed in the tubular fluid. If the tubule cells secrete sufficient H+, all HCO3 in the tubular fluid is reab-sorbed in this manner.