Which type of muscle tissue would excrete lactic acid leading to decreased oxygen affinity of hemoglobin?

• A. Skeletal muscle
• B. Cardiac muscle
• C. Smooth muscle
• D. Nerve tissue

Answer: (A)

Skeletal muscle is the correct choice as it is primarily responsible for voluntary movements and is the muscle type most active during intense exercise. When skeletal muscle is exercised vigorously, it can switch to anaerobic respiration to meet energy demands, particularly when oxygen levels are low. This anaerobic metabolism produces lactic acid as a byproduct, which can lead to a decrease in the pH of the surrounding environment.

As lactic acid accumulates, it can influence the affinity of hemoglobin for oxygen. The presence of lactic acid and the associated decrease in pH can promote the release of oxygen from hemoglobin, a phenomenon known as the Bohr effect. This physiological response ensures that active muscles receive more oxygen when they need it most, as hemoglobin is less effective at holding onto oxygen in acidic conditions.

In contrast, cardiac muscle and smooth muscle typically rely more on aerobic metabolism and are less likely to produce lactic acid under normal physiological conditions. Nerve tissue is not directly involved in muscle contractions and does not produce lactic acid in the same way skeletal muscle does. Thus, the relationship between lactic acid production, decreased pH, and oxygen affinity of hemoglobin specifically aligns with the function and metabolic behavior of skeletal muscle during high-intensity activity.