Question

1. Assume your blood has a pH of 7.4 and you have been producing urine with a pH of 7.4 for a while. You drive to very high altitude (ca. 4,000 m) and spend several hours there. Your alveolar ventilation rate increases (as expected), and eventually this causes your blood pH to rise above 7.4 (your blood plasma becomes more basic than normal). \newline This change in blood pH will initiate compensatory homeostatic mechanisms in your kidneys ("renal compensation") that will alter the pH of your urine so as to bring your blood pH back down toward the normal value of 7.4. What pH will your urine have to be in order to begin to drop your blood pH back toward normal? \newline If you're having trouble answering questions like this one which deal with blood pH buffering, try thinking about the concentration of protons in the blood first, then convert your answer to be expressed in the context of the pH scale after you arrive at the correct answer. For example, for this question, approach it this way: when you go to altitude, your blood gets more basic than it should be, so the concentration of protons in the blood is too low. To fix this problem, should your urine contain: \newline (A) a lower concentration of protons than it usually does (more basic than normal) (B) the same concentration of protons that it usually does (C) a higher concentration of protons than it usually does (more acidic than normal)?

A Higher than 7.4 (more basic than normal).

B 7.4.

C Lower than 7.4 (more acidic than normal).

2. Which of the following is a physiological response that you would expect to detect in someone who has recently begun a strenuous aerobic workout?

A Feedforward commands from brain respiratory rhythmicity centers that decrease alveolar ventilation rate.

B Decreased cardiac output.

C Decreased synthesis of glycogen from glucose in the liver.

D Sensory feedback from joint proprioceptors that decreases alveolar ventilation rate.

E Increased total peripheral resistance.

F Increasing blood insulin levels.

Answer 1

1. Research works have shown that with a higher altitude, respiratory alkalosis happens and renal compensation is one that is expected to happen as an outcome. Here, it is seen that urine pH will continue to rise above 7.4 and will come back to baseline after 24 hours. Therefore option (b) which is 7.4 is the correct answer as the urine pH comes back to normal 7.4, renal compensation happens and respiratory alkalosis gets corrected.

2. The correct answer here is option (c). This is because, during the initial phase of a strenuous aerobic exercise, the source of energy is the skeletal muscles and not glycogen from liver. It is only after fatigue that glycogen reserves in liver will begin to be utilised.