Biological Systems MCAT Practice Exam

What are venules?

1. Small arteries

2. Small veins just after capillaries

3. Bidirectional vessels

4. Thick-walled blood vessels

The correct answer is: Small veins just after capillaries

Venules are small blood vessels that serve as the primary conduit from the capillaries back to the larger veins. They collect deoxygenated blood from the capillary beds, where the exchange of gases, nutrients, and waste occurs. As capillaries converge, they form venules, which are characterized by thinner walls compared to arteries and a larger lumen, allowing them to accommodate the return flow of blood. This structure facilitates the collection of blood from multiple capillaries, allowing for efficient transport back toward the heart. In contrast, small arteries, bidirectional vessels, and thick-walled blood vessels do not accurately describe venules. Small arteries are responsible for carrying oxygenated blood away from the heart, bidirectional vessels suggest a functionality not typical of venules, and thick-walled blood vessels typically refer to arteries, which need to withstand higher pressures from the heart's pumping action. Thus, venules distinctly fit the description of small veins located just after capillaries.