What is the function of veins in the circulatory system?

Veins play a crucial role in the circulatory system by returning blood to the heart from capillaries. After oxygen and nutrients are delivered to the tissues, the deoxygenated blood collects in the capillaries. From there, it flows into larger veins, which transport the blood back to the heart. This function is vital for maintaining proper circulation, as it ensures that deoxygenated blood reaches the heart for re-oxygenation in the lungs. The design of veins, including their valves, prevents backflow and helps facilitate this return journey against the force of gravity, particularly in the limbs.

The other functions described in the choices relate to different aspects of the circulatory system. For example, arteries carry blood away from the heart to various tissues, while the exchange of materials between blood and cells primarily occurs at the capillary level. Absorbing excess fluids involves the lymphatic system rather than the circulatory system specifically. Thus, the primary and distinctive function of veins is indeed to return blood to the heart from the capillaries.