Optional for extra understanding Control of Blood pH by Respiratory Rate (a) The

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Optional for extra understanding Control of Blood pH by Respiratory Rate (a) The partial pressure of CO, in the lungs can be varied rapidly by the rate and depth of breathing. For example, a common remedy to alleviate hiccups is to increase the concentration of CO2 in the lungs. This can be achieved by holding one's breath, by very slow and shallow breathing hypoventilation), or by breathing in and out of a paper bag. Under such conditions, pCOz in the space of the lungs rises above normal. Qualitatively explain the effect of these procedures on the blood pH. (b) ) A common practice of competitive short-distance runners is to breathe rapidly and deeply (hyperventilate) for about half a minute to remove CO2 from their lungs just before the race begins. Blood pH may rise to 7.60. Explain why the blood pH increases. During a short-distance run, the muscles produce a large amount of lactic acid (CH3CH (OH)COOH, Ka = 1.38 x iO-4M) from their glucose stores. In view of this fact, why might hyperventilation before a dash be useful? (c) Consider this equation:

Explanation / Answer

1.

Hypoventilation leads to an increased CO2 concentration in the blood.

This causes blood pH to decrease (respiratory acidosis)

CO2 + H2O -----> H2CO3 -----> H+ + HCO3-

As the CO2 concentration increases, the reaction proceeds to the right (Increased production of acid).

Hypoventilation also leads accumulation of lactic acid in the blood due to anaerobic respiration.

2.

Short distance runners hyperventilate their lungs before the run.

This reduces the CO2 concentration in the blood.

CO2 + H2O -----> H2CO3 -----> H+ + HCO3-

So, the production of acid decreases. Hence the pH increases.

At high oxygen concentrations, only aerobic respiration occurs. So, no lactic acid production as well.

3.

Lactic acid is produced during anaerobic respiration via fermentation.

Glucose ------> Pyruvate -------> Lactate

Lactate production occurs only in the anaerobic/hypoventilation conditions.

Short distance runners use high amounts of oxygen due to their burst of running. So, they might deplete their blood oxygen levels.

Hence, they practice hyperventilation before the start of the race.

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