I remember hearing as a kid that blood in our veins is blue due to lack of oxygen, and that’s why veins look blue in light-skinned people. Recently I’ve heard it’s not true at all; blood in the veins is just lighter red than in the arteries, but red just the same. So what’s the truth?
Of course your blood is red. Blood drawn with a needle will still be red, even though there isn’t air to react with it. That said, there are shades of redness. The Mailbag Speaks.
I´m going out on a limb here, but I guess since venous blood is laden with carbon monoxide, it indeed should be a brighter shade of red than oxygen carrying blood on the arteries; the same way store meat is treated with CO to make it look more “natural”.
Both oxygenated (arterial blood) and non-oxygenated (venous blood) hemoglobin look red, although the llight absorption spectra differ slightly, and the color of oxygenated hemoglobin is a brighter red than that of non-oxygenated hemoglobin, which is a dark purplish red color. There should be no carbon monoxide in the blood, however, the color of CO-hemoglobin is closer to that of Oxy-hemoglobin than to that of deoxy-hemoglobin. Superficial veins look blueish in contrast to the surrounding skin, but probably mostly because due to their blood content, they are darker than the surrounding tissue.
If your blood is laden with carbon monoxide, you’re in serious trouble because CO doesn’t like to let go of the haemoglobin, rendering it unable to take up oxygen, which is undesirable for living organisms - less problematic for packaged cuts of meat. CO turns blood pinkish.
Ah, ejem… carbon dioxide, sorry… :smack:
Does it turn blood more pinkish too?
I don’t think so - I thought it was more of a dark wine-red, but that colour might just be the depletion of the oxygen.
Oxygenated blood is bright red, venous blood is deep red, blood exposed to carbon monoxide is very bright red, making the skin of the deceased is cherry red.
I’ve seen a lot of blood; it’s all pretty red. Blood is not blue except in certain very unusual circumstances, and in some social circles. Arterial blood is definitely redder than venous blood. How much redder depends on the physiology of the person. Factors such as their cardiac output, lung function and peripheral circulation all contribute to the magnitude of the difference in oxyhemoglobin from the arterial to the venous side. Some folks start out with lower arterial saturation to begin with because of crummy lungs, for instance.
I haven’t seen blood get brighter red on exposure to air, but I’m not sure I’ve ever paid attention to that, I guess. A young person with normal physiology will have a paO2 (partial pressure of arterial oxygen in mm Hg) of close to 100 at sea level. If he has a normal oxy-hemoglobin dissociation curve, this is easily enough to give him a hemoglobin oxygen saturation of 100%. So his arterial blood is as bright red as it can get from exposure to oxygen. How much of that oxygen gets extracted on the venous side varies with a lot of factors, but say that his pO2 on the venous side drops to 35 or 40 and his O2 sat drops to 70% (again it depends on his oxyhemoglobin dissociation curve…)
When you expose that venous blood to room air the pO2 is about 160 mm Hg at sea level (21% X 760). This should, in fact, shift the hemoglobin back toward a higher saturation. It makes sense to me at least some of those red cells are gonna get redder. On the other hand the blood is starting to clot and a bunch of other things are going on, so I have to say I’ve never looked at a big pool of venous blood and watch it become redder.
The blood in veins is usually redder than the vein looks when you are just looking at it either through the skin or even directly at an exposed vein.
It’s true that carbon monoxide makes blood brighter red but I don’t think I’ve noticed it’s that much brighter than fully oxygenated blood. I’ve taken care of plenty of CO poisonings, all the way up to dead people, and I don’t remember ever thinking they were cherry red. CO does bind a lot more tightly than O2, so the venous side blood does not darken. Smokers can have pretty high CO levels (over 10%) but how red their blood is also depends on how well they are oxygenating it, and bad lungs can offset the CO effect.
ETA: there are varying levels of hemoglobin and various types of hemoglobin as well. These two factors would also affect the actual (formal) color of the blood.
On the other hand, blood in early 1970s action and horror movies looks like bright red paint.
For example, if you are a crustacean… 
They blood uses copper instead of iron as its oxygen binder, that gives their blood a greenish to blue colour.
The misconception in the OP is a common one, it comes from lessons in school explaining the circulatory system. In diagrams for school textbooks it is common to show the arteries as red and the veins as blue. examples:
http://www.communitymemorial.com/pics/services/BloodCirculation.jpg
http://www.isletmedical.com/images/circulat.gif
That’s because it’s easier to follow diagrams with two different colours than two different shades of red. People often misunderstand it, and think that blood actually IS blue.
There’s more to it than that – Veins seen through the skin look blue. It’s not just an artistic choice to illustrate textbooks with contrasting colors. Clearly some filtering is going on that makes the veins appear bluish or greenish through the skin, while arteries look reddish. It ought to be possible to show why this is with spectra of venous and arterial blood, and with absorption and/or scattering spectra of the tissues of the human body. But I’ve never seen such a demonstration. It would be interesting, and would be a useful explanation of why things look the way they do.
There are some cool pathologic situations that affect blood color. Cats that are given Acetaminophen, for example, have a chocolate-brown color blood due to methemoglobinemia.
Cite: http://www.blackwell-synergy.com/doi/abs/10.1111/j.1476-4431.1996.tb00034.x
I’ll never forget having a blood draw done for a pharmaceutical study and neglecting to keep pressure on the wound afterward. I looked down and saw a line of very dark purplish red blood trickling all the way down my arm. Against my pale skin it looked almost black.
LOL
This was the first thing I ever challenged by dad about. When you’re 6-7, dad is god and knows everything. When he told me this, I, for the first time, argued with him. A few weeks before, I had blood drawn from me and it was red when it came out…and I didn’t see how it had time to change from blue to red.
Don’t be scared son, that’s not real blood
And if you’re English royalty, it’s very blue indeed.
Was watching a show last night discussing what effects outer space would have on the human body (without the protection of a 14 million dollar NASA spacesuit) and one of the first would be Cyanosis.
Sort of interesting note.
Most of the blood drawn for medical purposes is taken from veins. It is generally the colour of a good red wine. To take blood from a vein, you put on a tourniquet, feel for a vein and stick a needle in it…not terribly complicated.
However, if one wishes to measure the oxygen and carbon dioxide concentrations of the blood one can take an arterial blood sample or arterial blood gas (ABG). To take blood from an artery (usually from the radial artery at the wrist or the femoral artery at the groin) you don’t apply a tourinquet, you feel for a pulse and you aim a needle at it until brighter red, pulsing blood fills your syringe without suction. This requires slightly more skill and is more painful as arteries lie deeper than veins. Some places use local anaesthetic for ABGs, the hospitals where I have worked expect people to just man up and deal with it.
Sometimes you’ll hit a vein when you mean to get an artery and the colour of the blood is one way of knowing, but it is a subtle difference rather that red/blue or red/purple. Badly hypoxic or cyanosed people will have less bright red arterial blood.
On one occasion I was sure I had taken a venous sample because it was so dark, however on testing it just turned out the patient had approximately double the concentration of carbon dioxide to oxygen in his blood because he had been on 100% oxygen in the ambulance.
Well, the reason the veins look blue under the skin is because of it absorbing different light spectra and allowing others to be reflected; since blue is the highest frequency spectrum (well, actually, violet is, but let that be our little secret, shall we?), more blue light gets reflected from the ambient light sources than, say, red (which, goes without saying, is the lowest-frequency light color).
Nurses in the Bloodmobile love me, because I have huge surface veins in my arms, and I’m very pale, so it’s ridiculously easy to find a good vein for me to donate blood. Looking at the bag afterwards, I can personally attest that at least my venous blood is a deep, almost purplish red.