Renal function curves and control of body fluids and arterial pressure.

The purpose of this paper has been to emphasize the extreme importance of the renal function curve in determining the long-term level of arterial pressure. The reason for this importance is that the renal-body fluid-pressure control system exhibits the phenomenon of "infinite feedback gain". This is, the arterial pressure will stabilize only when the intake and output of water and salt becomes exactly equal, and this occurs at only one very exact pressure level for any given renal function curve and given salt intake level. This renal mechanism for controlling the body fluids and simultaneously controlling the arterial pressure, because of its infinite feedback gain capability for controlling arterial pressure, requires that other pressure control mechanisms must interact with this mechanism either to alter the renal function curve or to make the animal change its intake of salt and water if the other pressure mechanisms are to have any effect on the long-term arterial pressure level. Therefore, in virtually any analysis of long-term arterial pressure regulation, the renal function curve or its mathematical equivalent plays a central role.