What are the two mechanisms by which ADH is released?
1) Increase in plasma tonicity: stimulates hypothalamic osmoreceptors and magnocellular neurons to shrink, signaling magnocellular neurons to release ADH; sharp spike in ADH when plasma osmolarity reduces to between 285-295mOsm/kg; **ADH is released WAY BEFORE you start to feel thirsty;
2) Decrease in MABP (blood loss) --> causes decreased baroreceptor stretch and firing (IX and X) --> causes sympathetic tone to increase --> further increasing ADH release. This mechanism also makes mechanism 1 more sensitive
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