What is the primary function of capillaries?

What is the primary function of capillaries?

• A. Blood storage
• B. Hormone production
• C. Electrical conduction
• D. Gas exchange

Answer: (D)

Gas exchange occurs across capillary walls. Their surfaces are formed by extremely thin, one-cell-thick endothelial layers arranged in a vast network, which creates a huge surface area and slows blood flow just enough to maximize diffusion. This setup lets oxygen move from blood into surrounding tissues and carbon dioxide move from tissues into the blood, with the lungs using the same diffusion process to load oxygen and unload CO2. Capillaries aren’t primarily for storing blood, producing hormones, or conducting electricity—roles handled by veins/arteries, endocrine glands, and nervous or cardiac tissue, respectively.

Gas exchange occurs across capillary walls. Their surfaces are formed by extremely thin, one-cell-thick endothelial layers arranged in a vast network, which creates a huge surface area and slows blood flow just enough to maximize diffusion. This setup lets oxygen move from blood into surrounding tissues and carbon dioxide move from tissues into the blood, with the lungs using the same diffusion process to load oxygen and unload CO2. Capillaries aren’t primarily for storing blood, producing hormones, or conducting electricity—roles handled by veins/arteries, endocrine glands, and nervous or cardiac tissue, respectively.