Blood

[juicyjamie18]

Is blood really blue, or red? This has been bugging me for years! My best friend and I have collectively asked about 5000 people and nobody knows!

[SteveD]

It's red. Venous blood is dark red and arterial blood is bright red.

[rja211077]

it's red. stick a knife in your wrist if you need proof.

[K99]

Its blue and when it comes into contact with oxygen it turns red thats why your veins are blue. I think anyway.

[jills]

blood, oxygenated or otherwise is RED.

[IndieSinger]

Just exactly which 5000 people did you ask, and did you remember to ask people over the age of 4?

[Farseer]

The colour of blood depends on what it has been in contact with, it is blue when theyre is little/no oxygen in it and red when theyre is oxygen in it.... so your answer is BOTH (stick a knife in your wrist wont work cuz then the blood gets oxygen in it :) if u did it in a vacuum then it wud stay blue i think)

[Lizi]

IndieSinger - that's just the kinda response I'd have given *I guess that's why he chose to ask here rather than me...* :( Watch out for this one - he asks some crackin' good questions!! lol

[SteveD]

Let�s get the facts right here once and for all. As I said in the first answer, blood is red. If it�s venous blood (poor in oxygen) it is dark red and if it�s arterial blood (rich in oxygen) it�s bright red. If you cut a vein, the blood which comes out will not become oxygenated and turn bright red on contact with the air; that can only happen in the lungs or in an artificial lung such as the oxygenator in the extracorporeal blood circuit of a heart-lung machine. The reason for this is that a very large surface area of the red cells of the blood must come into contact with a membrane (the walls of the alveoli of the lungs or the membrane of an oxygenator) in order to allow oxygen to diffuse through that membrane. This diffusion takes place because of the difference in the partial pressures of oxygen in the air we breathe (or the gas supplied to an oxygenator) and the blood. Red blood cells (which transport oxygen) are about 7 microns in diameter. The capillaries of the alveolar walls in the lungs have a similar diameter: consequently, there is a very high surface contact. This cannot be achieved in an oxygenator, but is compensated for by lowering the patient�s temperature and/or increasing the percentage of oxygen in the gas supplied.