Which blood vessel type has the thinnest walls, allowing exchange of substances with tissues?
A
Capillaries
B
Arteries
C
Veins
D
Venules
Correct Answer: Option A — Capillaries
Explanation:
Capillaries are the smallest blood vessels with extremely thin, single-cell-layer walls that permit efficient exchange of oxygen, nutrients, and waste products between blood and surrounding body tissues at the cellular level.