What effect does active skeletal muscle tissue have on hemoglobin's affinity for oxygen?

• A. It increases due to lower temperature
• B. It decreases due to lower plasma pH
• C. It remains unchanged regardless of conditions
• D. It increases due to higher plasma PCO2

Answer: (B)

Active skeletal muscle tissue has a significant effect on hemoglobin's affinity for oxygen due to several metabolic changes that occur during exercise. When skeletal muscles are active, they produce carbon dioxide and lactic acid, leading to a lower plasma pH. This reduction in pH enhances the release of oxygen from hemoglobin, a phenomenon known as the Bohr effect.

The Bohr effect describes how an increase in the concentration of carbon dioxide (PCO2) and a decrease in pH cause hemoglobin to have a lower affinity for oxygen. As active muscles generate more carbon dioxide through aerobic metabolism, the local environment becomes more acidic, which promotes the release of oxygen from hemoglobin to meet the increased oxygen demand of the muscle.

Therefore, the correct answer highlights the relationship between lower plasma pH (due to increased carbon dioxide and lactic acid production) and the decreased affinity of hemoglobin for oxygen under active muscle conditions. This physiological mechanism ensures that more oxygen is delivered to the tissues that need it most during periods of increased activity.