MadSci Network: General Biology
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Re: Blue Blood

Area: General Biology
Posted By: Prudence Risley, Collective Enigma Elucidator
Date: Wed May 22 16:31:05 1996


* Another teacher and I are having a disagreement. Most biology
diagrams show arteries in red print and veins in blue.. [..]

Your friend is indeed correct, though the difference in color between arteries and veins is more a difference of 'bright red' vs. a deeper shade of red/purple (scarlet vs. maroon e.g.). When hemoglobin, the molecule in red blood cells that carries oxygen and gives its red color, is bound to oxygen it is bright red. Vessels carrying oxygenated blood include all arteries going out to the body and the pulmonary vein -- this vein returns oxygenated from the lungs to the left side of the heart. The pulmonary artery is the only artery in the body that does not carry oxygenated blood. It runs from the right ventricle of the heart *to* the lungs so blood can be oxygenated. Thus 'oxygenation' is not a consistent characteristic of all arteries. The mnemonic we often used was *A* in Artery stands for Away from the heart, and indeed all arteries carry blood away from the heart while viens return blood to the heart.

Returning to blood color, hemoglobin releases its oxygen in the capillary beds of your body -- internal organs, muscles etc. Hemoglobin minus oxygen is maroonish-dark purple in color. To better distinguish the change in oxygenated/deoxygenated blood we use the red/blue designation.

As for distinguishing arteries from veins, viens are always easier to identify. They are much larger than arteries, and less muscular. Arteries and veins generally follow one another side by side, if you find a vein, a little poking around should reveal an adjacent artery.

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