Which mechanism redistributes cardiac output, directing more blood to skeletal muscles during exercise?

• A. Haemoglobin
• B. Myoglobin
• C. Vascular Shunt Mechanism
• D. A-VO2 Difference

Answer: (C)

During exercise, the body needs more blood in the working muscles, so it shifts blood flow away from less essential areas. This is done mainly by the vascular shunt mechanism, which involves arteriovenous shunts that can redirect blood from organs like the gut and kidneys toward exercising skeletal muscles. At the same time, sympathetic signals constrict vessels in nonessential beds while local factors in active muscles (such as CO2, H+, and adenosine) promote vasodilation, increasing blood flow to meet the muscles’ oxygen and nutrient demands.

Hemoglobin and myoglobin are about carrying and storing oxygen, not directing where blood goes. The A-VO2 difference measures how much oxygen is extracted by tissues, not how blood is redistributed.