OCR General Certificate of Secondary Education (GCSE) Biology Practice Exam

How are veins adapted to help blood flow back to the heart?

1. They contain high-pressure blood

2. They have thicker walls than arteries

3. They have larger lumens and contain valves

4. They are rigid and narrow

The correct answer is: They have larger lumens and contain valves

Veins are specifically adapted to facilitate the return of blood to the heart through several key features. One of the most important adaptations is their larger lumen, which reduces resistance to blood flow, allowing the blood to move more easily through the vessel. Additionally, veins contain valves that prevent the backflow of blood, ensuring that it flows in one direction—toward the heart. These valves are particularly crucial in the limbs, where blood must be transported against the force of gravity. The presence of these features means that even though the pressure in veins is lower than in arteries, they are efficient at returning blood to the heart by utilizing the larger lumen and the presence of valves to maintain unidirectional flow. This design is essential for the circulatory system to function properly, especially after physical activities where muscles assist in venous return through contraction and relaxation.