What do capillaries primarily facilitate in the body's tissues?

Capillaries play a crucial role in the circulatory system by facilitating the exchange of oxygen and nutrients between the bloodstream and body tissues. Their thin walls, composed of a single layer of endothelial cells, allow for efficient diffusion of oxygen from the blood into surrounding tissues where it is utilized for cellular respiration.

In addition to oxygen delivery, capillaries also enable the transport of other important substances, such as glucose and hormones, while simultaneously allowing for the pickup of carbon dioxide and other metabolic wastes from tissues. This dual function underscores the importance of capillaries in maintaining homeostasis.

While blood transportation is a function of larger blood vessels like arteries and veins, and heat dissipation can occur via blood flow through these vessels, neither directly characterizes the primary role of capillaries. Similarly, although capillaries assist in the removal of cellular waste, their main function in the context of the question is centered around oxygen delivery, making it the most accurate choice.