Veins vs. Arteries: Structural Adaptations for Blood Flow

Steps:

• Arteries carry blood away from the heart under high pressure, requiring thick, elastic walls to withstand and propel flow.
• Veins return blood to the heart under low pressure, needing a wider lumen to accommodate larger blood volume without resistance.
• Veins have thinner walls with fewer elastic and muscle fibers, relying on valves and skeletal muscle for flow direction.
• Compare options to match: veins feature wider lumen, thinner wall, fewer elastic fibres, fewer muscle fibres.

Why D is correct:

• Veins operate at low pressure, so their structure (wider lumen for volume, thinner wall with fewer elastic/muscle fibres) facilitates passive return flow, per circulatory system physiology.

Why the others are wrong:

• A: Describes arteries, not veins (narrower lumen and thicker wall suit high-pressure flow).
• B: Mixes traits incorrectly (thinner wall fits veins, but narrower lumen and more muscle do not).
• C: Inaccurate for veins (thicker wall and more elastic fibres are arterial features for pressure resistance).

Final answer: D