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In the sinusoids of the liver, venous blood from the hepatic portal system mixes with arterial blood from the hepatic arteries.

Do oxygen molecules move between oxygenated RBCs and non-oxygenated RBCs, so that the partial oxygen saturation of the blood in the sinusoids reflect partial saturation of the RBCs? Or do RBCs retain their initial oxygen saturation, so that the partial saturation of the blood in the sinusoids reflects a mixture of saturated and unsaturated RBCs?

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I am not sure if these are the best tags, feel free to adjust them is they can be improved. –  KennyPeanuts Dec 17 '11 at 12:17
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up vote 5 down vote accepted

The oxygen saturation (in lungs) and desaturation (in target organs) takes place via diffusion along the concentration gradient (i.e. partial pressure for gases). Therefore as long as RBCs from two different sources and having different partial pressure of oxygen mix up, the oxygen level starts to equilibrate between these cells.

But diffusion as a passive mechanism is not very fast and can take some time. So the only possibility for the second variant (there is a mixture of two types of RBCs) is if the mixture exists for very short time in liver sinusoids, so that the blood leaves them without really mixing completely up.

This is not true, at least in some animal models the blood within the liver seems to reach equilibrium very quickly and its resulting partial pressure can be influenced by adjusting the blood flow from different sources (using vasoactive substances injected directly, as in the referenced paper).

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I don't understand why you think that diffusion wouldn't be fast enough, since it is the same mechanism that ensures that blood becomes oxygenated in the pulmonary circulation, and deoxygenated in the peripheral tissues. –  Alan Boyd Oct 2 '12 at 16:33
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