Which of the following is/are true about the relationship between chloride (Cl–) and bicarbonate HCO3– in acid-base balance?

1. For each Cl– ion excreted into the urine, the blood gains an HCO3– ion.
2. Blood Cl– and HCO3– ion levels are reciprocally related.
3. People with chronically high CO2 tend to have low blood Cl– levels.
4. Activation of the NH3 buffer system enhances Cl– gain and HCO3 loss.
a. 2 and 3 only
b. 1, 2, and 3 only
c. 2 only
d. 2, 3, and 4 only

ANS: B
The net effect of ammonia buffer activity is to cause more bicarbonate to be reabsorbed into the blood, counteracting the acidic state of the blood. Figure 14-5 shows that when a Cl– ion is ex-creted in combination with an ammonium ion, the blood gains an HCO3– ion. Thus, blood Cl– and HCO3– ion concentrations are reciprocally related (i.e., when one is high, the other is low). This explains why people with chronically high blood PCO2 tend to have low blood Cl− concentra-tions. Activation of the ammonia buffer system enhances Cl– loss and HCO3– gain.