What function do capillaries serve in the body?

Capillaries play a crucial role in the circulatory system by facilitating the exchange of substances between blood and tissues. They are tiny blood vessels that connect arteries and veins and are characterized by their thin walls, which allow for the efficient transfer of oxygen, nutrients, and waste products.

The correct answer, which highlights the distribution of oxygen-rich blood to tissues, accurately reflects the primary function of capillaries. As blood flows through capillaries, oxygen diffuses from the blood into surrounding tissues, where it is used for cellular respiration. At the same time, carbon dioxide and other waste products from the tissues diffuse into the capillaries to be carried away for elimination from the body.

The other options do not correctly describe the primary role of capillaries. For instance, the transportation of large blood cells does not occur through capillaries, as they are too small to accommodate such cells. While capillaries do play a part in nutrient exchange, their main function is not to store excess nutrients, and filtration processes are predominantly carried out by organs like the kidneys, not by capillaries themselves.