A Level Biology Practice Exam

What are venules in the circulatory system?

1. Large blood vessels that deliver oxygenated blood

2. Small blood vessels that collect blood from the capillaries and lead into the veins

3. Thin-walled vessels where gas exchange occurs

4. Vessels that carry blood away from the heart

The correct answer is: Small blood vessels that collect blood from the capillaries and lead into the veins

Venules are small blood vessels that serve a crucial role in the circulatory system by acting as conduits for blood returning from the capillaries back to the veins. After blood has delivered oxygen and nutrients to tissues through the capillaries, it is collected by the venules. These vessels facilitate the flow of deoxygenated blood, which is crucial for maintaining efficient blood circulation in the body. The structure of venules is designed for this specific purpose; they have thin walls that allow for some exchange of substances and have a smaller diameter than veins. This makes them well-suited to collect blood from the capillary beds, where the exchange of gases, nutrients, and waste products occurs. The ability of venules to connect capillaries to larger veins is essential for the proper functioning of the circulatory system, ensuring that blood is efficiently returned to the heart for reoxygenation and to continue its journey through the body. The other options do not accurately describe venules or their function in the circulatory system. Large blood vessels that deliver oxygenated blood would refer to arteries. Thin-walled vessels where gas exchange occurs describes capillaries, not venules. Vessels that carry blood away from the heart refer to arteries as well.