Osmoreceptors in the hypothalamus monitor the water potential of the blood. When the water potential is low, the cells shrink and stimulate neurosecretory cells to produce ADH. ADH flows down the axon to the posterior pituitary where it is stored. When the neurosecretory cells are stimulated they send impulses to the pituitary which releases ADH into the blood. ADH is broken down slowly by enzymes and has a half-life of 20 minutes.