Blood Vessels

Blood vessels form the network of tubes that carry blood throughout the body. There are three main types: arteries, veins and capillaries. Each has a specific structure suited to its function.

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Overview of Blood Vessels

Blood leaves the heart in arteries, passes through capillaries where exchange occurs, and returns to the heart in veins.

The order is always: Heart → Arteries → Arterioles → Capillaries → Venules → Veins → Heart

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Arteries

Arteries carry blood away from the heart.

Structure

• Thick muscular walls — the smooth muscle layer can contract and relax to help push blood along and regulate blood flow
• Thick elastic tissue layer — allows the artery wall to stretch and recoil with each heartbeat, smoothing out the surges of high pressure
• Small lumen (the hollow centre) — maintains high blood pressure
• No valves (except semilunar valves at the very start in the pulmonary artery and aorta)
• Lined with endothelium — a smooth inner layer that reduces friction

Key Features of Blood in Arteries