Healthy humans have a pH of around 7.4 (slightly basic.) But if you hooked up the blood as a battery how much electric voltage would one generate, what is the standard electrode potential?
This seems to me like it should be important for stuff such as transporting ions across the cell membrane.
If I think about it this question basically comes down to if things like iron tend to dissolve $\ce{Fe -> Fe^{2+} + 2e^-}$ (SEP of 0.44) or precipitate $\ce{Fe^{2+} + 2e^-->Fe}$ in human blood.
Because of important chemicals like haemoglobin I think the SEP should be around 0.44 but differs depending upon whether cells are absorbing oxygen from it or recharging it with oxygen. Maybe this would even vary depending on whether heavy exercise is happening.