What is the function of capillaries?

What is the function of capillaries?

• A. To serve as the site of gas exchange between the blood and air (in the lungs) or the blood and body's cells
• B. To pump blood to the lungs
• C. To regulate heart rate
• D. To store blood

Answer: (A)

Capillaries specialize in exchange. Their walls are extremely thin, formed by a single layer of endothelial cells, and they form an extensive network between arteries and veins. This structure gives blood a large surface area and slows its flow just enough to allow diffusion to occur efficiently. In the lungs, capillaries surround the tiny air sacs (alveoli), so oxygen can diffuse from the air into the blood and carbon dioxide can diffuse from the blood into the air to be exhaled. In body tissues, oxygen and nutrients pass from the blood into cells, while waste products move into the blood for removal. That diffusion-driven transfer is the primary role of capillaries. Pumping blood to the lungs is a job of the heart and pulmonary vessels, heart rate is regulated by the nervous and hormonal systems, and storing blood is a function of veins and the heart, not capillaries.

Capillaries specialize in exchange. Their walls are extremely thin, formed by a single layer of endothelial cells, and they form an extensive network between arteries and veins. This structure gives blood a large surface area and slows its flow just enough to allow diffusion to occur efficiently. In the lungs, capillaries surround the tiny air sacs (alveoli), so oxygen can diffuse from the air into the blood and carbon dioxide can diffuse from the blood into the air to be exhaled. In body tissues, oxygen and nutrients pass from the blood into cells, while waste products move into the blood for removal. That diffusion-driven transfer is the primary role of capillaries. Pumping blood to the lungs is a job of the heart and pulmonary vessels, heart rate is regulated by the nervous and hormonal systems, and storing blood is a function of veins and the heart, not capillaries.