|MadSci Network: Biochemistry|
Diffusion of different gases from the blood into tissues or from tissues into blood depends on the difference in partial pressures of a gas on the two sides. e.g. the partial pressure of oxygen in the arterial blood is 95 mmHg and in the tissue spaces is 40 mmHg and therefore there is a net pressure of 55 mmHg that pushes oxygen from blood into the tissues. You may ask here why the oxygen is low in the tissues. This is because the tissues continuously consume oxygen so the oxygen partial pressure tends to fall whereas the blood in arteries has much oxygen as it is continuously oxygenated in the lungs. Similarly the carbon dioxide tends to diffuse out of the tissues into the blood because it is high in the tissues due to continuous production i.e. 45 mmHg and in the arterial blood it is 40 mmHg. Thus net pressure of 5 mmHg pushes the carbon dioxide out of the tisseus into the blood. I hope its clear; if there is any confusion feel free to ask me.
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