What is the primary role of capillaries in the circulatory system?

The primary role of capillaries in the circulatory system is to facilitate the exchange of gases, nutrients, and waste products between the blood and surrounding tissues. Capillaries are small, thin-walled vessels that form a vast network throughout the body, allowing for efficient transfer of substances due to their large surface area and proximity to cells.

As blood flows through capillaries, oxygen from the blood passes into tissues while carbon dioxide and other metabolic waste products move from the tissues into the blood. This exchange is crucial for maintaining homeostasis and supporting cellular functions. The structure of capillaries, being one cell layer thick, is specifically designed to optimize this exchange process.

In contrast, while transporting blood and connecting arteries to veins are important functions of the circulatory system, they pertain more to the role of larger vessels such as arteries and veins. Regulating blood pressure is primarily managed by the heart and larger blood vessels through contractile mechanisms and resistance changes in the vascular system. Thus, the focus on the unique role of capillaries emphasizes their key function in nutrient and gas exchange, making the correct answer particularly relevant.