Which vessels are tiny, thin-walled, and carry nutrients and oxygen into cells while removing waste CO2?

Which vessels are tiny, thin-walled, and carry nutrients and oxygen into cells while removing waste CO2?

• A. Capillaries
• B. Veins
• C. Arteries
• D. Cardiovascular system

Answer: (A)

Exchange of nutrients, oxygen, and waste happens in the capillaries, the smallest and thinnest vessels in the network. Their walls are a single layer of endothelial cells, with a tiny basement membrane, making the barrier very thin. This setup lets oxygen and nutrients diffuse out of the blood into surrounding tissues and lets carbon dioxide and other wastes diffuse from cells into the blood to be carried away. The extensive capillary networks provide a huge surface area and the short distance for diffusion, making exchange efficient. Arteries have thicker walls to withstand high pressure as blood is pumped from the heart, veins have thinner walls and carry blood back toward the heart, and the cardiovascular system refers to the entire circulation rather than a single vessel type.