Question

2. a. Parietal cells control the concentration of HCl in the stomach by secreting H+ and Cl-. While fasting, they maintain stomach pH at 3.0. After a meal, they decrease stomach pH to 1.4. What is the fold-change in [H+] from fasting to after a meal?

b. For every H+ ion secreted into the stomach, parietal cells also secrete a HCO3- ion into blood plasma. HCO3- plays an important role in maintaining the pH of blood plasma (see textbook page 45 for equations). Patients with achlorhydria have impaired HCl secretion and thus have a loss of HCO3- in the blood. What will be the blood pH of a achlorhydria patient with half the normal concentration of HCO3- in the blood? Assume a constant CO2(d) of 1.2 mM and a normal HCO3- of 24 mM.

c. The pH of the stomach can influence the ionization of drugs such as Aspirin (aka acetylsalicylic acid or HAsp). Given that at equilibrium the pH of a 0.1 M Aspirin is 2.24, what is the pKa of Aspirin?

d. Using the pKa from c., what is the ratio of Asp- to HAsp in the stomach of the patient after a meal?

Would the ratio of Asp to HAsp increase, decrease or stay the same if the patient had fasted?

Answer 1