Hi! Great question. Veins do carry darker red blood, but it isn’t empty of oxygen — it just has less oxygen than the bright red blood that leaves the heart.
- The heart is a pump. It pushes bright red, oxygen-rich blood out through tubes called arteries.
- Blood brings oxygen to your body. When blood goes through your muscles and other parts, it gives oxygen to them. That makes the blood a bit darker.
- Veins bring the darker blood back to the heart. The veins are the return roads that carry that darker blood back so the heart can send it to the lungs.
- The lungs add oxygen. In the lungs the blood gets fresh oxygen and becomes bright red again. Then the heart sends it out again.
One special thing: The veins that come from the lungs (pulmonary veins) carry bright red blood because they are bringing oxygen-rich blood back to the heart.
Why do veins sometimes look blue under your skin? That is because of how light shines through your skin and how your eyes see it — the blood is still red, just darker, not blue.
Easy way to remember: arteries = bright red going out, veins = darker red coming back. You can draw a heart, draw red arrows going out and dark red arrows coming back to practice!