Blood is the red liquid that flows through your body, carrying oxygen and nutrients to every cell while taking away waste products. Your heart pumps blood through miles of tubes called blood vessels, creating a delivery system more efficient than any postal service.

Blood gets its red color from millions of tiny cells called red blood cells, which contain a substance called hemoglobin that grabs oxygen from your lungs and releases it wherever your body needs it. Blood also contains white blood cells that fight off germs and infections, acting like your body's security team. When you get a cut, special cells called platelets rush to the site and help form a clot, like an emergency repair crew patching a leak.

An adult body contains about five quarts of blood, constantly circulating to keep you alive and healthy. Without blood flow, your brain would shut down in minutes and your other organs would quickly follow.

The word appears in many expressions too. Blood relatives share family connections through birth rather than marriage. When something makes your blood boil, you're extremely angry. Bad blood between people means lingering anger or resentment. And if you keep your cool under pressure, people might say you have ice in your veins instead of blood.