Science Monday: Do We Really Have Blue Blood?

Learn a new fact for the week: why is blood in our veins a different color than what we bleed — and is it really as blue as it looks?

This heart shows both red arteries, and blue veins. It is also plastic, which is a good thing, because if it was real, its owner would be dead. You know, with it not being in a chest cavity. Photo by Robina Weermeijer.

I remember, as a small child, leafing through a book that showed all the different organs and structures inside the human body. (Thankfully, these were drawn diagrams, rather than photos, so it merely encouraged my curiosity instead of scarring me for life.)

One feature that I noted were that some of the blood vessels were drawn in a bright, cheery red, while others were drawn in a robin’s-egg blue. Curious, I showed the picture to my mother, a doctor.

“That’s to point out the veins versus the arteries,” she explained, pointing down at the picture. “See, the arteries all flow away from the heart, and they’re red. The veins all flow towards the heart, and they’re blue.”

This made a lot of sense. I even looked down at my own forearm, watching how the blood vessels would stand out against my pale skin when I flexed my little-kid muscles. I could see the blue lines of the veins, just below the surface of the skin.

Strangely enough, however, whenever I happened to get a cut or scrape, the blood that came out was bright red — never blue. Did I never get cut on a vein?