ADH
                                ===

þ Functions of ADH
 - acts at distal collecting tubules to increase Na+ reabsorption
 - causes vasoconstriction of mesenteric arterioles
 - osmoreceoptors
  + in anterior hypothalamus
  + respond to tonicity, not osmolality (i.e., no effect from increased urea,
    as this is permeant into the receoptor cells)

þ Osmoreceptor effects:
   275 mOsm/L -- normal
   280 mOsm/L -- ADH secretion starts
   290 mOsm/L -- thirst starts
   295 mOsm/L -- enough ADH secreted to maximally concentrate urine

þ other stimuli to ADH release:
 - nausea (but not vomiting per se)
 - left atrial and aortic baroreceptors
 - things that reset the osmostat:
  + diuretics
  + changes in aldosterone levels
  + pregnancy