Which of the following is likely during vigorous exercise?

• A. Blood flow to the kidneys increases
• B. Blood flow to the kidneys decreases
• C. Blood flow to the brain stops
• D. Blood flow to the skin decreases

Answer: (A)

During vigorous exercise the body's blood flow is redistributed to meet the needs of active muscles and heat dissipation. The autonomic nervous system raises sympathetic tone, causing vessels feeding nonessential organs to constrict. This means the kidneys receive less blood flow, and renal perfusion drops temporarily as blood is shunted toward working muscles and the skin for cooling. The kidney’s filtering activity falls accordingly, and urine production slows during the activity.

At the same time, blood flow to skeletal muscles rises dramatically to supply oxygen and nutrients for contraction, and skin blood flow increases to help dissipate heat. Brain perfusion is preserved by autoregulation, so it does not stop; the brain continues to receive adequate blood flow.

So, a typical change during vigorous exercise is reduced blood flow to the kidneys, with increased flow to muscles and skin, while brain circulation remains stable.