IMAT 2018 Q23 [Exercise]

Which of the following can be a result of exercise in a healthy human?

  1. a decrease in muscle pH
  2. an increase in blood pH
  3. more blood flows to certain organs

A. 1 and 2 only
B. 1 and 3 only
C. 1, 2 and 3
D. 3 only
E. 2 and 3 only

The answer to this question is B, only statements 1 and 3 are correct.

Let us rationalize each of the statements to further understand the rationale of the correct answer!

  1. "a decrease in muscle pH": Let’s tackle this in an inferential manner. Decrease in pH means that there is an increase in acidity. Where then would acidity come from within the muscle? Remember that the muscle uses ATP as energy to stimulate contraction. The production of ATP requires numerous substrates, one of which is NAD+. Why is NAD+ relevant? Remember, that in glycolysis, one of the reactants needed to make ATP is NAD+. Under abundant O2 concentrations, NAD+ is regenerated by the electron transport chain. In exercise, there will come a point that the work exerted on the muscles exceeds the immediate supply of oxygen. Without oxygen, we know that the electron transport chain won’t work. This decreases the ability of the muscle cell to regenerate NAD+ for ATP production, which now creates the objective of regenerating NAD+ without using oxygen, to continue creating ATP. How? This can be achieved using lactic acid fermentation. At the end of glycolysis, pyruvate can be acted upon by the enzyme called lactate dehydrogenase to regenerate NAD+ AND produce lactic ACID. It now makes sense, that the acidity that was mentioned in this statement can be attributed to LACTIC ACID. This makes this statement a correct consideration.

  2. "an increase in blood pH": An increase in blood pH means the blood is becoming more alkaline. There are 2 main scenarios wherein the blood can become more alkaline: first, the bicarbonate levels in the blood increase. However, this is more of a pathologic phenomenon that is not relevant in this question since there is mention that this is a “healthy human”. Second, the carbon dioxide levels can decrease. You might be tempted to think, during exercise the increasing breathing rate must mean there is increased elimination of CO2 from the body. However, keep in mind, that the organs involved in exercise are involved with increased cellular respiration to maintain the demands of exercise. And as you already know, increase cellular respiration means there is also the increase production of CO2 as a by-product! Meaning, the elimination of CO2 through the faster breathing rate is enough to prevent the blood from being too acidic, but at the same time, it is not enough to make the blood more alkaline given that the cells are producing more CO2 according to the demands of exercise. All of this then makes the statement an incorrect consideration.

  3. "more blood flows to certain organs": This is undeniably a correct statement. The central concept to this is basically maintaining the oxygen supply to an organ that has an increased oxygen demand due to exercise. How exactly does the body maintain the oxygen supply needed by an organ? The body increases the blood flow to the different organs that need it in different scenarios, which in this case, would be exercise. An example would be the skin, which is the biggest organ of the human body! During exercise, there is a need to release heat and maintain temperature homeostasis. One of the ways this can be achieved is to increase blood flow to the skin and facilitate heat transfer! Another example would be the increased cardiac output during exercise, which increases the blood flow to the respiratory system! This makes sense since the body would need to have a way to eliminate the CO2 produced during the increased cellular respiration. An important example as well would be the increase blood flow to the muscles, which facilitates the actions needed during the specific exercise!

Thus, the only correct answer for this question is choice B.