On the viability of a physiological system. Regulation of potassium by aldosterone.

Physiological systems maintain their variables within limits through regulatory processes. We have studied potassium regulation on the basis of the viability theory. The viability kernel is determined by taking into account the constraints of the variables of the dynamical system, i.e. the set of initial states for which there exists at least one viable trajectory. The set of regulations which maintain the viability of the physiological system is also determined. Finally, we investigate the influence of various strategies that allow the choice of one control among the viable regulations.