What is the primary function of capillaries in the circulatory system?

The primary function of capillaries in the circulatory system is to connect arteries and veins, facilitating the exchange of nutrients, gases, and waste products between the blood and surrounding tissues. Capillaries are the smallest blood vessels, and their thin, permeable walls allow for efficient diffusion of substances. This exchange is crucial for maintaining the body's homeostasis, as it ensures that tissues receive the oxygen and nutrients they need while also allowing for the removal of carbon dioxide and metabolic wastes.

In contrast to this primary function, arteries are responsible for transporting blood away from the heart, while veins return blood to the heart. The storage of blood for emergencies generally involves larger vessels like veins or specialized storage areas within the body. Protection against pathogens is primarily carried out by the immune system rather than through the specific function of capillaries.