Perfusion refers to which of the following?

• A. The movement of air into and out of the lungs
• B. The exchange of gases between blood and tissues
• C. The passage of fluid to a tissue
• D. The production of mucus in airways

Answer: (C)

Perfusion is the delivery of blood to tissue through the circulatory system. It involves the movement of fluid (blood) through the capillary network to reach cells, supplying oxygen and nutrients and removing waste. This matches the idea of the passage of fluid to a tissue.

Air moving into and out of the lungs is ventilation, not perfusion. The exchange of gases between blood and tissues is gas exchange (diffusion at the capillaries), and mucus production is a secretory process in the airways. So, perfusion specifically refers to the blood flow delivering fluid to tissues.