Which statement best describes the histological and functional differences between arterioles and venules?

• A. Arterioles have thin walls with minimal smooth muscle; venules have thick walls and regulate flow.
• B. Arterioles and venules have identical walls; only their size differs.
• C. Arterioles have thicker smooth muscle and regulate flow; venules have thin walls and collect blood; valves are common in larger veins.
• D. Venules have smooth muscle larger than arterioles; arterioles lack muscle.

Answer: (C)

Arterioles and venules differ in wall structure and function: arterioles have a well-developed tunica media rich in smooth muscle that lets them constrict or dilate to regulate resistance and direct blood flow into capillary beds, while venules are thin-walled vessels with little smooth muscle that collect blood from capillaries and move it toward larger veins; valves are commonly found in larger veins to prevent backflow in the low‑pressure system. This matches the statement because it correctly assigns thicker smooth muscle and flow regulation to arterioles, and thin-walled, collecting function to venules, with valves typical of larger veins. The other options misstate wall thickness, muscle content, or valve location, which would not align with the known histology and functions.