Regulation of Extracellular Sodium & Water Flashcards Preview

CVPR: Renal > Regulation of Extracellular Sodium & Water > Flashcards

Flashcards in Regulation of Extracellular Sodium & Water Deck (6)
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Naconcentration detection @ ECF

  • Na = major osmotic substance @ ECF ==> osmotic equilibrium w/cells
  • losses/gains in Na ==> changes in ECF volume (vs. Na concentration)
  • Due to the two-fold greater volume of the cellular over the ECF compartment, gains (or losses) of sodium from the ECF result in two-fold greater changes in ECF volume than they do in ECF sodium concentration. 
  • Major sensors monitor volume ==> mean arterial pressure (MAP) of major arteries


Feedback loop for sodium regulation

  • e.g. sodium loss ==> decrease ECF volume/MAP decrease
  • ==> increased baroreceptor reflex ==> increased renin ==> AgII ==> increased aldosterone (@ adrenal cortex)
  • aldoseterone ==> increased Na reabsorption @ distal tubule and collecting duct


Feedback loop for water reabsorption

  • regulation of water = monitoring of ECF volume and osmolarity
  • severe sweating ==> decreased ECF volume ==> decreased LA filling pressure ==> increased baroceptor reflex to hypothalamus
  • ==> activated ADH-synthesizing neurons ==> secrete ADH from post. pituitary
  • ==> increased water reaborption @ late distal tubule + collecting duct
  • ALSO: increased ECF osmolarity ==> activation of hypothalmic osmoreceptors ==> activated ADH-synth neurons


Severe diarrhea implications for water regulation

  • severe diarrhea ==> isotonic loss of 3 L of ECF ==> activation of low volume pathway ==> increased ADH secretion
  • consume 2L of hypotonic water during recovery ==> decrease osmolarity ==> inhibition of ADH pathway
  • which one wins?


Main mechanism of ECF water regulation

  • primarily an osmoregulatory system w/emergency low-volume override
  • water is regulated to acheive osmotic constancy; however at low volumes ADH rapidly dominates osmotic effects 
  • low volume dominance of ADH secretion ==> defense of circulation in severe hypovolemia


Regulation of volume overload

  • no suppression of ADH if volume increases above normal
  • atrial natriuretic peptide (ANP) located at heart ==> potent diuretic hormone + increases sodium excretion
    • increase filtration via dilation of afferent and efferent arterioles
    • decreases ADH secretion
    • inhibits renin secretion/aldosterone
    • prevents effects of remaining levels of ADH and aldosterone