What is the primary role of capillaries?

What is the primary role of capillaries?

• A. Pump blood through the heart.
• B. Exchange of oxygen, nutrients, and waste between blood and tissues.
• C. Carry blood away from the heart.
• D. Return blood to the heart.

Answer: (B)

Capillaries are the site of exchange between blood and tissues. Their walls are only one cell thick, creating a very short diffusion distance, and they have a huge total surface area with slow blood flow. This setup allows oxygen and nutrients to diffuse from the blood into tissue cells and enables carbon dioxide and other wastes to diffuse from cells back into the blood for removal. The heart’s job is to pump blood; arteries carry blood away from the heart; veins return blood to the heart. Capillaries themselves don’t actively pump or transport large volumes—they are the primary exchange vessels in the microcirculation.

Capillaries are the site of exchange between blood and tissues. Their walls are only one cell thick, creating a very short diffusion distance, and they have a huge total surface area with slow blood flow. This setup allows oxygen and nutrients to diffuse from the blood into tissue cells and enables carbon dioxide and other wastes to diffuse from cells back into the blood for removal. The heart’s job is to pump blood; arteries carry blood away from the heart; veins return blood to the heart. Capillaries themselves don’t actively pump or transport large volumes—they are the primary exchange vessels in the microcirculation.