Transport of Oxygen in the Dissolved
State
At the normal arterial PO2 of 95 mm Hg, about 0.29 mil-liliter of oxygen
is dissolved in every 100 milliliters of water in the blood, and when the PO2 of the blood falls to the
normal 40 mm Hg in the tissue capillaries, only 0.12 milliliter of oxygen
remains dissolved. In other words, 0.17 milliliter of oxygen is normally
transported in the dissolved state to the tissues by each 100 milli-liters of
arterial blood flow. This compares with almost 5 milliliters of oxygen
transported by the red cell hemo-globin. Therefore, the amount of oxygen
transported to the tissues in the dissolved state is normally slight, only
about 3 per cent of the total, as compared with 97 per cent transported by the
hemoglobin.
During strenuous exercise, when hemoglobin release of oxygen to the
tissues increases another threefold, the relative quantity of oxygen
transported in the dissolved state falls to as little as 1.5 per cent. But if a
person breathes oxygen at very high alveolar PO2 levels, the amount
transported in the dissolved state can become much greater, sometimes so much
so that a serious excess of oxygen occurs in the tissues, and “oxygen
poi-soning” ensues. This often leads to brain convulsions and even death, in
relation to the high-pressure breathing of oxygen among deep-sea divers.
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