Veins

circulatory system · blood vessels · body systems

One-way highways. Veins carry blood back toward your heart, always moving in one direction. Tiny valves inside veins act like one-way doors to keep blood from flowing backward.

Mostly tired blood. Most veins carry deoxygenated blood, which means the blood has already dropped off its oxygen in your body's tissues and is heading back to get more. It's like a delivery truck returning to the warehouse after dropping off packages.

Returning home. While arteries rush blood away from your heart, veins bring it back in. This cycle happens millions of times every day to keep you alive.

Thinner than arteries. Veins have thinner, more stretchy walls than arteries because the blood moving through them is under less pressure. Your veins can hold extra blood when you need it.

Found everywhere. Almost every animal with a heart has veins, from tiny fish to enormous whales. They are essential for any creature that needs to move blood around inside its body.