An osmoreceptor is a sensory receptor primarily found in the hypothalamus of most homeothermic organisms that detects changes in osmotic pressure.
If plasma osmolarity rises above 290 mOsmol/L, then water will move out of the cell due to osmosis, causing the neuroreceptor to shrink in size.
The calcium ions binds to the synaptotagmin 1 sub-unit of the SNARE protein attached to the arginine-vasopressin (AVP) containing vesicle membrane.
Subsequent release of AVP into the posterior pituitary gland occurs, whereby vasopressin is secreted into the blood stream of the nearby capillaries.
Angiotensin II exerts system wide effects, triggering aldosterone release from the adrenal cortex, direct vasoconstriction, and thirst behaviors originating in the hypothalamus.