What are the exchange vessels where nutrients and gases pass between blood and tissues?

What are the exchange vessels where nutrients and gases pass between blood and tissues?

• A. Capillaries
• B. Arterioles
• C. Venules
• D. Veins

Answer: (A)

Exchange happens across capillaries, the tiny vessels that connect arteries to veins. Their walls are only a single cell thick, made of endothelium with a thin basement membrane, sometimes with pericytes. This ultra-thin barrier, along with a vast network and slow blood flow, lets oxygen and nutrients move from blood into the surrounding tissues while carbon dioxide and other wastes diffuse the opposite way. Different tissues have slightly different capillary types—continuous capillaries in most tissues, fenestrated in some organs for faster exchange, and sinusoidal capillaries in the liver and bone marrow to accommodate larger molecules—but all serve the same core role: the actual site where nutrients and gases cross between blood and tissues. Arterioles and venules mainly regulate flow and carry blood to and from capillary beds, not the primary exchange surface.

Exchange happens across capillaries, the tiny vessels that connect arteries to veins. Their walls are only a single cell thick, made of endothelium with a thin basement membrane, sometimes with pericytes. This ultra-thin barrier, along with a vast network and slow blood flow, lets oxygen and nutrients move from blood into the surrounding tissues while carbon dioxide and other wastes diffuse the opposite way. Different tissues have slightly different capillary types—continuous capillaries in most tissues, fenestrated in some organs for faster exchange, and sinusoidal capillaries in the liver and bone marrow to accommodate larger molecules—but all serve the same core role: the actual site where nutrients and gases cross between blood and tissues. Arterioles and venules mainly regulate flow and carry blood to and from capillary beds, not the primary exchange surface.