Diffusion of Oxygen from the Peripheral Capillaries to the Tissue Cells
Oxygen is always being used by the cells. Therefore, the intracellular PO2 in the peripheral tissue cells remains lower than the PO2 in the peripheral capillar-ies. Also, in many instances, there is considerable phys-ical distance between the capillaries and the cells. Therefore, the normal intracellular PO2 ranges from as low as 5 mm Hg to as high as 40 mm Hg, averaging (by direct measurement in lower animals) 23 mm Hg. Because only 1 to 3 mm Hg of oxygen pressure is normally required for full support of the chemical processes that use oxygen in the cell, one can see that even this low intracellular PO2 of 23 mm Hg is more than adequate and provides a large safety factor.