.Physiolibrary.Media.Blood.SubstancesPort .Physiolibrary.Media.Blood.SubstancesPortElectrochemical connections lead via free base substance forms. For example, the total mass fraction of carbon dioxide is represented as part of the composition of blood in fluid connector, but free dissolved carbon dioxide in blood plasma or bicarbonate in blood plasma are its electrochemical connectors proposed to model the electrochemical CO2 fluxes. Since the selected forms are precisely determined by the composition of the blood, it is not necessary to store them and pass them through the fluid connector. They are only expressed and calculated when needed.