Which choice best describes the function of capillaries in the circulatory system?

Capillaries play a crucial role in the circulatory system by facilitating the exchange of nutrients, gases, and waste products at the cellular level. They are the smallest blood vessels in the body, forming a network between arterioles and venules. The thin walls of capillaries, composed of just a single layer of endothelial cells, allow for efficient diffusion of oxygen and carbon dioxide as well as the transfer of nutrients and waste materials between blood and surrounding tissues.

This exchange process is vital for maintaining homeostasis and supporting cellular metabolism. Nutrients from the blood, such as glucose and amino acids, can easily pass through the walls of the capillaries and enter the tissues, while waste products produced by the cells can move in the opposite direction to be carried away for excretion. This function highlights the importance of capillaries in ensuring that cells receive the necessary substances for energy production and growth and that metabolic waste does not accumulate.

In contrast, the other choices refer to functions primarily associated with different components of the circulatory system. Transporting oxygen specifically to the brain, carrying blood back to the heart, and regulating blood pressure involve larger vessels (arteries and veins) and various mechanisms not directly related to the primary role of capillaries.