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How do capillaries connect arteries and veins?

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Silhouette diagram of the human body highlighting the heart and major blood vessels, with labeled arteries in red and veins in blue to show the structure of the cardiovascular system. — Circulatory system Human circulatory system.

Capillaries serve as the essential link between the arterial and venous sides of the circulatory system. The process functions as follows:

Arterial Flow: Blood is transported from the heart through arteries, which branch into smaller vessels called arterioles.12
Capillary Exchange: Arterioles empty into extensive networks of microscopic capillaries. These vessels consist of a single layer of endothelium, allowing for the efficient exchange of oxygen, nutrients, and waste products between the blood and bodily tissues.123
Venous Return: As blood exits the capillary beds, it enters small vessels known as venules. These venules merge into larger veins, which eventually return the blood to the heart.14

This transition is highly regulated; arterioles and muscular gatekeepers called sphincters control the flow of blood into the capillary networks, directing it to the tissues that require it most.234