Regulation of Water and Electrolytes

TO INCLUDE a discussion of the regulation of total body water and electrolytes in such a symposium OIn the cardiovascular system at first glanee may require some justification. It should be quickly apparent, however, that the total body fluids and the circulatory system are so intimately interrelated that consideration of one without the other would be quite incomplete. Part of the body fluids, the cellular fluids of erythrocytes and the plasma, are distributed within the vascular system and constitute the medium, so to speak, upon which the circulatory systenm operates. Being that which is circulated, these fluid phases are an integral part of the eirculatory system. Likewise the circulatory system is essential to the integrity of the fluids of the body. The eirculation provides the mixing apparatus that maintains the homogeneity of multiple and widely separated portions of the body fluids and the circulation is the link of the organs of exchange with the external enlvironment. It would seem proper, therefore, to include water and electrolytes in this discussion of regulation of the cardiovascular system. The concept of regulatioii as already defined by our moderator can be applied to the body fluids as well as to the rest of the cardiovascular system. In the consideration that follows. I shall attempt to show not only that physiologic servomechanisms are operative but that a great deal remains to be learnied of their moduts operandi. The emphasis will be on the holes in, rather than the substance of, our knowledge.