ACSM Health Fitness Specialist Practice Test

The primary function of capillaries is indeed the exchange of nutrients. Capillaries are the smallest blood vessels in the human body, and they play a crucial role in the circulatory system by facilitating the transfer of oxygen, nutrients, and waste products between the blood and the tissues. Their thin walls, composed of a single layer of endothelial cells, allow for easy diffusion of substances.

In the context of the question, while capillaries do participate in transporting oxygen, it is primarily in relation to their function in nutrient exchange and overall metabolic processes. This exchange is essential for providing cells with the materials they need for energy production and for the removal of waste products generated by cellular metabolism.

The other functions mentioned involve processes that are more specific to other types of blood vessels. For instance, veins are tasked with carrying blood back to the heart, while arteries primarily transport oxygenated blood away from the heart. The absorption of waste products could be interpreted as part of the exchange process, but it is secondary to the core function of nutrient exchange that takes place across capillary networks. Therefore, recognizing the role of capillaries in facilitating nutrient exchange helps to clearly define their primary function in the body.