What role do capillaries play in the circulatory system?

Capillaries serve a crucial role in the circulatory system by connecting the arterial system, which carries blood away from the heart, to the venous system, which returns blood back to the heart. This network of tiny blood vessels facilitates the exchange of substances between the blood and the tissues. Through their thin walls, capillaries allow oxygen, carbon dioxide, nutrients, and waste products to pass between the blood and surrounding cells. This connection is essential for maintaining tissue health and ensuring that cells receive the necessary nutrients while removing waste products effectively.

The other options relate to specific functions or characteristics of the circulatory system but do not accurately define the unique role of capillaries. For instance, while veins do return deoxygenated blood to the heart and arteries transport oxygen-rich blood, these functions pertain directly to those vessel types rather than the capillaries' role in bridging these two systems. Capillaries do not absorb nutrients directly in the intestines, nor do they produce blood cells, which occurs in the bone marrow. Thus, the correct identification of capillaries’ function as the connectors between arteries and veins highlights their vital importance in the circulatory framework.