A blood vessel is any of the tube-like structures that carry blood throughout your body. Think of them as highways for your blood, creating a vast network that reaches every part of you, from your brain to your toes.

Your body contains three main types of blood vessels. Arteries carry oxygen-rich blood away from your heart to your muscles, organs, and tissues. Veins bring blood back to your heart after it has delivered its oxygen. And tiny capillaries, thinner than a single hair, form the connections between arteries and veins, allowing oxygen and nutrients to pass into your cells.

If you could lay out all the blood vessels in your body end to end, they would stretch about 60,000 miles, enough to circle the Earth more than twice. This vast system works continuously, with your heart pumping blood through these vessels about 100,000 times each day.

You can sometimes see blood vessels through your skin as blue or purple lines, especially on your wrists or the back of your hands. When a doctor checks your pulse, they're feeling blood flowing through an artery. When you get a small cut, you've broken tiny capillaries near the surface of your skin, which is why you bleed.