Red Blood Cells

Red blood cells are tiny cells that float in your blood. Their main job is to carry oxygen from your lungs to every part of your body. They also carry carbon dioxide back to your lungs so you can breathe it out.

How They Work

Red blood cells contain a protein called hemoglobin. Hemoglobin grabs onto oxygen in your lungs. Then the red blood cells travel through your blood vessels to deliver oxygen everywhere.

Hemoglobin is what gives blood its red color. When red blood cells are full of oxygen, your blood is bright red. When they drop off the oxygen, the blood becomes darker.

Making New Red Blood Cells

Your body makes new red blood cells inside your bones, in a soft material called bone marrow. Your body creates about two million new red blood cells every second.

Each red blood cell lives for about 120 days. Then your body breaks it down and makes a new one. Eating iron-rich foods like spinach helps your body make healthy red blood cells.

Fun Facts

• A single drop of blood contains about five million red blood cells.
• Red blood cells are shaped like tiny doughnuts without the hole.
• Red blood cells do not have a nucleus, which gives them more room to carry oxygen.

Did You Know?

If you lined up all the red blood cells in your body end to end, they would wrap around the Earth about four times!