A tiny blood vessel where substances are exchanged between the blood and body cells is a

A tiny blood vessel where substances are exchanged between the blood and body cells is a

• A. Arteriole
• B. Capillary
• C. Vein
• D. Venule

Answer: (B)

The site where substances are exchanged between blood and body cells is the capillary. Their walls are extremely thin—only a single layer of endothelial cells—so oxygen, nutrients, and hormones can diffuse out to tissues, while carbon dioxide and wastes diffuse into the blood for removal. The tiny diameter of capillaries also slows blood flow just enough to maximize contact time, making diffusion efficient. Capillary networks are extensive and reach nearly every cell, ensuring tissues get what they need and wastes are carried away. Arteries and arterioles deliver blood with thicker, muscular walls under higher pressure, while veins and venules carry blood back to the heart and are structured more for transport and storage rather than direct exchange. So capillaries are the vessel best suited for exchange between blood and cells.

The site where substances are exchanged between blood and body cells is the capillary. Their walls are extremely thin—only a single layer of endothelial cells—so oxygen, nutrients, and hormones can diffuse out to tissues, while carbon dioxide and wastes diffuse into the blood for removal. The tiny diameter of capillaries also slows blood flow just enough to maximize contact time, making diffusion efficient. Capillary networks are extensive and reach nearly every cell, ensuring tissues get what they need and wastes are carried away. Arteries and arterioles deliver blood with thicker, muscular walls under higher pressure, while veins and venules carry blood back to the heart and are structured more for transport and storage rather than direct exchange. So capillaries are the vessel best suited for exchange between blood and cells.