In capillaries, what is primarily exchanged between blood and body tissues?

In the capillaries, the primary function is to facilitate the exchange of substances between blood and body tissues. This exchange primarily involves nutrients and waste products. Oxygen and glucose, while important for cellular metabolism, fall under the broader category of nutrients. Nutrients such as amino acids, fatty acids, and glucose are delivered from blood to tissues for energy and growth, while waste products such as carbon dioxide, urea, and other metabolites are transported from the tissues back into the blood for elimination.

The structure of capillaries, being thin-walled and designed for selective permeability, assists this exchange process effectively. The large surface area and close proximity to tissues ensure that efficient transfer can occur, making nutrients and waste products the central focus of this physiological function.

While carbon dioxide and hormones are indeed exchanged in the capillaries, they do not encapsulate the primary role of nutrient delivery and waste removal. Platelets and white blood cells are components of the blood that play roles in healing and immune response rather than in nutrient and waste exchange. Therefore, the correct answer reflects the fundamental physiological processes that occur in the capillaries, emphasizing the significance of nutrients and waste products in maintaining homeostasis.