h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Haemoglobin carries oxygen from the lungs to the bodys tissues. Does it also carry carbon dioxide back or is there some other mechanism involved?

Carbon dioxide is far more soluble in water than oxygen, so it doesn't need haemoglobin to carry it. It just dissolves in the blood and is carried to the lungs. How much carbon dioxide can dissolve is determined by the pH of the blood, which is one of the reasons why regulation of acid-base balance in the blood is vital.

Haemoglobin does bind to carbon monoxide, which prevents oxygen from binding. This is how carbon monoxide poisoning kills.

Thanks Danny That makes sense.

I knew about the carbon monoxide, what about nitrous oxide? There was a thing in the paper years ago about a kid who died laughing because the mask he was huffing with didn't provide for air.

Nitrous oxide apparently has a *very* small effect on haemoglobin similar to that of carbon monoxide, but the boy that you mention probably died of straightforward lack of oxygen.

I presume that was just a straightforward case of suffocation, unlike carbon monoxide poisoning, where the carbon monoxide actually prevents the oxygen from being delivered.

Some beasties (lobsters for instance) don't use haemoglobin as a means of carrying oxygen around their bodies - they use something copper-based. One of the consequences of that is that they can't be poisoned with CO in the same way that you or I can.

dosn't cyanide attack haemoglobin as well

hydrogen cynaide is known as a blood agent in the field of chemical weapons

Cyanide compounds don't affect haemoglobin. They bind the the enzyme cytochrome oxidase in mitochondria, which means that affected cells are unable to use oxygen in respiration and therefore die. Tissues that are highly dependent on aerobic respiration, particularly the brain, are very susceptible to disruption of these metabolic pathways, hence the toxicity of cyanide.

Some antidotes for cyanide poisoning act by converting haemoglobin to methaemoglobin, which binds cyanide more strongly than cytochrome oxidase.