On the Nervous System Integration of Water and Salt Metabolism

To a remarkable degree cerebral homeostasis depends upon the integrated activity of discrete intracranial receptors and effectors. Thus, a medullary cardioregulatory area alters pulse and blood pressure so as to secure optimal cerebral blood flow, while a nearby respiratory area so regulates pulmonary exchange that an abundant oxygen supply reaches the neuron. Cerebral metabolism is further influenced by the adenohypophyseal thyrotrophic and adrenocorticotrophic secretions which are regulated by hypothalamic neurohumoral activity.¹It is particularly important that the intracranial fluid content be regulated, for the brain is surrounded by fluid, both within and without, while remaining profoundly fluid in its own composition. Cerebral function is delicately susceptible to intracellular and extracellular alterations of salt and water, and here, too, the brain itself provides the regulating structures. Indeed, 3 aspects of water-electrolyte balance are subject primarily to intracranial regulation: the intake of sodium, and the consumption and excretion of water; in