What do capillaries facilitate in the circulatory system?

Capillaries play a crucial role in the circulatory system primarily by facilitating the exchange of gases between the blood and tissues. These tiny blood vessels form an extensive network throughout the body and provide the surface area necessary for this exchange to occur efficiently.

Oxygen from the blood diffuses through the thin walls of the capillaries into the surrounding tissues, where it is utilized for cellular respiration. Conversely, carbon dioxide, a waste product of this process, diffuses from the tissues back into the blood for transport to the lungs, where it will be expelled from the body. This exchange is vital for maintaining proper cellular function and overall metabolic processes.

The structure of capillaries—a single layer of endothelial cells—enables this effective diffusion, allowing substances to move easily between the blood and surrounding tissues. This function is central to sustaining life, as it ensures that tissues receive the oxygen and nutrients they require while simultaneously removing waste products.