Okay, I think this is misleading..
1.) Because why would you increase aldosterone?? yes, aldosterone increases Na+ reabsorption but it is also followed by Osmosis of water, so, water will be increased --> plasma concentration is still decreased. (p. 1040 of T&D)
2.) Another, if less ANP is released, so low Natriuresis or low Na+ lost in Urine, then there will be high plasma volume following Na+ reabsorption via obligatory water reabsorption in the proximal convoluted tubule and still decreased osmolarity. (p 1041 of T&D)
3.) This you have said "
Decrease in osmolarity (low sodium) causes loss of water from plasma/interstitial fluid by osmosis into cells." This is a scenario wherein you have decreased osmolarity in plasma and interstitial fluid because of a lot of fluid loss mechanisms but you still take in a whole lot of water. This is Hyponatremia. (p. 1067 of T&D)
If there is decreased osmolarity (so there is high plasma volume) ie. Taking 25L of water:
--> decreased ADH release --> low aquaporins 2 --> low blood volume --> promotes Diuresis --> more urine --> increased plasma osmolarity.
--> increased BV -> increased blood pressure -> lesser Renin, Angiotensin II, and aldosterone to promote Natriuresis and Diuresis --> more urine --> lesser BP -> lesser BV --> increased plasma osmolarity.
--> more stretch in atrium bcoz of high BV and BP--> more ANP --> vasodilation of afferent aterioles --> more GFR --> promotes Natriuresis to prevent water reabsorption by Osmosis to further prevent increased plasma volume (prevent decreased plasma concentration)--> more Urine produced
--> lesser blood volume --> increased plasma concentration.
That's it. Renal Superphysiology.
Ka-me Ha-me WAVE!!!!!
