What occurs in the capillaries?

In the capillaries, the primary function is the exchange of substances between the blood and surrounding tissues. This crucial exchange involves the transfer of water, nutrients, gases, and waste products. The walls of capillaries are extremely thin, allowing for efficient diffusion of these substances. Nutrients and oxygen from the blood can move into the tissue cells, while carbon dioxide and metabolic wastes from the tissues enter the capillaries to be carried away.

This process is vital for maintaining the homeostasis of body tissues, providing them with necessary elements for metabolism and removing harmful byproducts. Other options, while related to the circulatory process, do not accurately represent what occurs specifically in capillaries.