Blood in veins, IS blue right?

Comments on Cecil's Columns/Staff Reports
#1

http://www.straightdope.com/mailbag/mbloodrd.html

Yes, I know its very old, I’m in Science 30 at school and the topic of blood color in veins comes up a few times when studying the human circulatory system.

In this Staff Report it states that Blood traveling through veins in not in fact blue like we see it, but a dark red. The explanation is the whole light wavelengths, absorbtion in skin, faulty colors thing. Which, does make sence after I thought about it.

What I question is this:

And this:

Alright, the experiments had a flaw. Look, if I were to slice open my vein right now its obvious that blue blood would not squirt all over the place. Keep in mind, that Veins have blood that has No oxygen in it. If I were to slice my vein open the “Blue” blood would immediately touch our oxygen filled air, and instantly become red again. Giving us the idea that it is always red in the first place.

In the experiments they both drew blood from veins, but the moment that the blood was drawn it came into contact with oxygen filled containers; it became dark red.

Perhaps the only way to properly prove that Veinous blood is blue, is by exposing an open vein in outer space? What do you think?

#2

Naw, blood in the veins is actually yellow with purple spots. But as soon as anyone looks at it, the light rays from their eyes makes it look red.

No, Teelo, blood is never blue.

#3

Venous blood is less bright red than arterial blood, but as Dex says, it’s never blue.

I can see you don’t understand how blood is drawn. The syringe is injected into the vein with the piston pushed fully to the bottom. This means the the only air in it is in the needle. Given that the needle is about 20 mm long (and that’s generous) and has an ID of less than a millimeter (let’s say a millimeter to be generous, too), the total volume of air is about 15.7 cubic mm–tiny in relation to the total blood volume drawn. That is the only air the blood comes into contact with while being drawn.

#4

Ask anybody, such as Mrs. FtG, who work in hospitals, clinics or some such and are around “fresh” blood all the time. Nowadays, they use vacutainers to draw blood samples. Notice the “vacu”. Next time you get your blood drawn, look at the tube when it fills. That’s dark red Teelo juice that hasn’t been exposed to air. Ditto the blood in transfusion packs, etc. And it has to come from veins, drawing blood from arteries is a definite no-no for phlebotomists.

It is very dark red, so the light bouncing out of your skin adds a lot of color to it plus the color contrast effect we all learned about in Psych 101.

#5

Maybe when you’re dead. I don’t have exact numbers handy, but venous blood should have somewhere around half to two-thirds as much oxygen as arterial blood, presuming you’re at rest and breathing ordinary air at atmospheric pressure.

#6

ftg is right, Teelo – blood drawn from a vein enters a syringe or a container that has no air. It wouldn’t be a good idea to expose it to air, because in addition to the air fouling up any blood oxygen measurements, it would expose it to bacteria, mold spores, etc., and that would be a Bad Thing.

#7

Vacutainers have air–it’s only a partial pressure, not a complete vacuum–but I’m not sure what kind of air.

#8

To put some more realistic numbers into QED’s calculation,
a typical venous sampling needle is 23 gauge, which is only 0.33mm in inside diameter. That’s only about 0.85 cubic millimeters per cm of needle. And air is only 21% or so Oxygen, so the amount of oxygen is only around 0.17 cubic millimeters. Blood can hold about 20% Oxygen (by volume), so that 0.17 cubic millimeters of Oxygen can only oxygenate about 1 cubic millimeter of blood. A typical blood sample might be 10 cc’s, 10,000 times that, so the amount of Oxygen in the needle is only going to oxygenate that venous blood to about 0.01%.

#9

A pool of blood on the floor, even many mm deep, is bright red (I’ve cleaned it up in the past), the color is not at all like the color of sealed bag blood in Red Cross offices.

Textbooks use brightly colored diagrams to show how your cirulatory system works. Why would they ever think to color the blood vessels accurately? Dark red and bright red would be misleading, it would be hard to tell the veins from the arteries. Bright red and bright blue is much better for diagrams. But don’t mistake textbook diagrams for reality. (In fact, be very distrustful of textbooks in the first place, especially public school textbooks for grade school and middle school.)

#10

Really? I thought they were partly pressurized with nitrogen rather than air. No?

#11

Vacutainers do contain a small amount of inert air. They can also contain other factors for maintaining the blood properly, e.g., anti-coagulant. There is a color code on the caps for which vacutainer to use for what kind of test.

Note in particular that for blood gas workups, heparin containing vacutainers are used (green cap). There cannot be any oxygen in the vacutainer as it would mess up the test big time.

#12

I think that even if there were oxygen in the vacutainers, the blood would not instantly oxygenate. The lungs are complex organs that provide tremendous surface area for gas diffusion. A drop or vial of blood provides far less surface area exposed to air. If such a small surface area could oxygenate blood very quickly, the lungs wouldn’t have to be nearly as complex as they are.