blood

[luigibrau]

why is blood red

[theprof]

It's all down to haemoglobin. This is the specialised chromoprotein that is made up of a protein (known as a globin) combined with a ferrous iron containing pigment (called a haem). Haemoglobin makes up around 90% of red blood cells and is red in colour.

Each haemoglobin molecule contains four atoms of ferrous iron, one in each haem group, which can combine with four molecules of oxygen. In the lungs the haem part of the haemoglobin combines with oxygen to form oxyhaemoglobin and the resultant arterial blood is scarlet in colour. The oxygen is locked into the red blood cell and from there it's transported around the body for the tissues to use in their own manner.

When the oxygen is released from the molecule in the tissues, haemoglobin acquires a bluish colour which is why blood in the veins has a bluish-red tinge.

Tissues do not completely deplete the red blood cells of oxygen. Arterial blood going to the tissues contains around 98% oxygen whereas venous blood returning to the lungs still contain about 70% oxygen.

Each 100ml of blood contains around 18g of haemoglobin or put another way, each red blood cell contains around 300 million molecules of haemoglobin.

[eleanswers]

whoa!! I bet the above answer was a little more than luigibrau bargained for. Great answer, I can't compete with that, however what I will say is blood is only red when exposed to 'white' light. As with anything, colour is dictated by absorbsion and reflection of white light ie: from the sun. Blood would not be red under different lighting conditions. So is it red at all?

[theprof]

Your in the realms of colour perception here eleanswers and that is a subject in itself.

I think we can regard blood as being red for most purposes because most people do see it in full spectrum light.

If you're interested in that type of thing, do some research on optical brighteners. These complex chemicals are included in virtually all washing powders bought nowadays and they fool the eye into believing that slightly grey clothes coming out of the washing machine are bright-white.

It's curious they don't advertise Lux Flakes nowadays.

Ah well, time to get off my SOAP-box (chuckle!)

[eleanswers]

It took me a while but I finally get the joke, or is that irony? (soap box, Lux) ha..

Lux is still advertised as a bathroom soap, to wash skin. Do you think this face soap also contains Silbene? What if the soap doesn't actually clean us but applies a coating of optical brightners.. giving a false appearance that we really are clean & white. Maybe we Europeans were of black skin colour before soap was introduced.

[theprof]

No it was a joke. As I was typing it all out, it was just a chain of thought. Lux flakes are pure, flaked soap packed in a box ergo soap box! Terrible joke I know but I will try to get out more.

I've never considered the possibilities of using optical brighteners in soap and it's a good point. Haven't you ever seen people walking around with what looks like an uneven suntan? Perhaps it down to them not washing themselves evenly and/or using a cheap soap.

Perhaps we are all dark-skinned beneath after all. I think I'll start the ball rolling today in university by starting a trial involving getting my students to not wash, shower or bath for a month. If my students' skin gets progressively darker, we might well conclude that it's all because of the lack of contact with optical brighteners. After all, what else could influence it ;-)