Fig. 24From: Fluid and ion transfer across the blood–brain and blood–cerebrospinal fluid barriers; a comparative account of mechanisms and rolesConsequences of adding lactic acid to ISF. In a the lactic acid dissociates and the lactate− is transported out of the ISF leaving the H+ behind. H+ combines with HCO3 − and forms CO2 and H2O both of which can diffuse into the blood. Each molecule of lactic acid added reduces the number of HCO3 − ions present in ISF by one. In b the lactic acid is transported out of the ISF to blood as lactic acid (or by cotransport of lactate− and H+). There is no immediate relationship between [HCO3 −]ISF and either the rate of addition of lactic acid or [lactate−]ISF Back to article page