Hypothalamic integration ofbodyfluid regulation

Theprogression ofanimallife fromthe paleozoic oceantorivers anddiverse econiches ontheplanet's surface, aswellasthesubsequent reinvasion oftheocean, involved manydifferent stresses onionic pattern, osmotic pressure, andvolumeoftheextracellular fluid bathing body cells. Therelatively constant ionic pattern ofvertebrates reflects agenetic "set" ofmanyregulatory mechanisms- particularly renal regulation. Renalregulation ofionic pat- ternwhenlossoffluid fromthebodyisdisproportionate relative totheextracellular fluid composition (e.g., gastric juice withvomiting andpancreatic secretion withdiarrhea) makesmanifest thatamechanism toproduce abiologically relatively inactive extracellular anionHCO3exists, whereas nocomparable mechanism toproduce abiologically inactive cation hasevolved. Life intheocean, whichhasthree times the sodiumconcentration ofextracellular fluid, involves quite different osmoregulatory stress tothatinfreshwater. Terres- trial life involves riskofdesiccation and,inlarge areas ofthe planet, salt deficiency. Mechanisms integrated inthehypo- thalamus (theevolutionary ancient midbrain) control water retention andfacilitate excretion ofsodium, andalsocontrol thesecretion ofreninbythekidney. Overandabovethe multifactorial processes ofexcretion, hypothalamic sensors reacting tosodiumconcentration, aswellascircumventricu- larorgans sensors reacting toosmotic pressure andangio- tensin II, subserve genesis ofsodium hunger andthirst. These behaviors spectacularly augmenttheadaptive capacities of animals. Instinct (genotypic memory) andlearning (pheno- typic memory)aremelded togive specific behavior apttothe metabolic status oftheanimal. Thesensations, compelling emotions, andintentions generated bythese vegetative sys- temsfocus theissue ofthephylogenetic emergence ofcon- sciousness andwhether primal awareness initially camefrom theinteroreceptors andvegetative systems rather thanthe distance receptors. Inthehigher mammals, thefunctions centered inthehypo- thalamus playa paramount roleinintegrating themany physiological systems controlling themilieu interieur. These hypothalamic processes rangefromgenetically determined patterns ofingestive behavior that correct bodydeficits and, in turn, involve associated cognitive andmemoryfunctions ofthe cortex, totheother extremeofthecontrol ofexcretory processes, inamodeapttothemetabolic status oftheanimal. Someevolutionary aspects ofbodyfluid control willbe described first asageneral biological context ofthemecha- nisms inmammals.