Also, blood found in a relatively large vein is much closer to the body average than that found in a capillary area, where much of the liquid is from extracellu

Also, blood found in a relatively large vein is much closer to the body average than that found in a capillary area, where much of the liquid is from extracellular space and not even coming from within blood vessels. Of course, extracellular space is filled from blood serum, but a lot of stuff has different concentrations in ECF.