Oxygen delivery is a major function of the circulation, and the reason that blood hemoglobin concentration is so high. The oxygen content of arterial blood is constant at 19-20 ml/dl (Figure 1.05).
In contrast, venous oxygen content varies from organ to organ, tissue to tissue, dependent on aerobic needs and blood flow. For the heart at rest, venous O2 content is only 5-6 ml/dl, for skeletal muscle it is about 13 ml/dl, and for kidney it is about 16 ml/dl. The difference in O2 content between arterial blood entering an organ and venous blood leaving is the A-V O2 difference. This is quite different for the heart, at 14-15 ml/dl, from that of the kidney, at just 2-3 ml/dl.
Two exceptions to the statement are the adult pulmonary artery which carries venous blood and the umbilical vein. The former carries venous blood (i.e. low oxygen content), while the latter carries arterialized blood of a higher oxygen content than that in the umbilical artery.
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