Question

Capacitance vessels have in their wall:

• A. More elastic tissue and less muscle
• B. Less elastic tissue and more muscle
• C. More elastic tissue and more muscle
• D. Less elastic tissue and less muscle

Hint:

Capacitance vessels are veins, which act as the body's low-pressure blood reservoir.

Answer 1

The Correct Option is D

Step 1: The question is really asking you to identify the wall makeup of veins, since veins are the body's capacitance (reservoir) vessels that pool the bulk of circulating blood.

Step 2: Think about function. A reservoir must expand easily under low filling pressure. A wall packed with elastin would recoil strongly and a wall packed with smooth muscle would resist stretch. Veins do neither, so logically their wall must be poor in both components.

Step 3: Histology confirms this. In a vein the media is thin with sparse smooth muscle, and the elastic fibres are few and disorganised, lacking the well defined internal and external elastic laminae that arteries show. The wall is dominated by loose connective tissue instead.

Step 4: Contrast with arteries: the aorta and large arteries are elastic, and small arteries and arterioles are muscular. Each option pairing that adds more elastin or more muscle therefore points to an artery, not a vein. The only pairing left for a capacitance vessel is less elastic tissue and less muscle.

\[\boxed{\text{Less elastic tissue and less muscle}}\]