Which vessels are primarily responsible for exchange of gases, nutrients, and wastes between blood and tissues?

Which vessels are primarily responsible for exchange of gases, nutrients, and wastes between blood and tissues?

• A. Capillaries
• B. Arteries
• C. Veins
• D. Lymphatic vessels

Answer: (A)

The key idea is that substance exchange between blood and tissues happens across the very walls of the smallest blood vessels: the capillaries. Their walls are thin—just a single layer of endothelial cells—providing a tiny diffusion distance and a huge surface area so oxygen, carbon dioxide, nutrients, and wastes can move by diffusion and filtration between blood and surrounding cells. Arteries and veins transport blood to and from tissues but have thicker walls and are not the main sites for exchange. Lymphatic vessels collect interstitial fluid and participate in immune functions, but they don’t mediate direct gas and nutrient exchange with tissues. A concrete example is in the lungs, where oxygen and carbon dioxide diffuse across the capillary walls surrounding the air sacs. So, the vessels responsible for exchange are capillaries.

The key idea is that substance exchange between blood and tissues happens across the very walls of the smallest blood vessels: the capillaries. Their walls are thin—just a single layer of endothelial cells—providing a tiny diffusion distance and a huge surface area so oxygen, carbon dioxide, nutrients, and wastes can move by diffusion and filtration between blood and surrounding cells. Arteries and veins transport blood to and from tissues but have thicker walls and are not the main sites for exchange. Lymphatic vessels collect interstitial fluid and participate in immune functions, but they don’t mediate direct gas and nutrient exchange with tissues. A concrete example is in the lungs, where oxygen and carbon dioxide diffuse across the capillary walls surrounding the air sacs. So, the vessels responsible for exchange are capillaries.