What does the posterior pituitary gland and the hypothalamus have in common with one another and what are their individual functions?

The hypothalamus is a region of the brain that controls number of bodily functions. It is located in the middle of the base of the brain.

ADH: also known as vasopressin and AVP, arginine vasopressin is a posterior pituitary hormone responsible for re absorption of water from collecting ducts of the kidneys. Without ADH we will have too much urine. Deficiency of ADH is responsible for what is called diabetes insipidus which is characterized by too much urine, and people with this disease state are treated by giving them external bills containing certain amount of ADH.

As for oxytocin : its release stimulates uterine contraction and release of milk from mammary glands After birth, stimulation of the breast by the infant feeding stimulates the posterior pituitary to produce oxytocin. 

  The hypothalamus controls pituitary gland via hypothalamic releasing factors. The supraoptic and paraventricular nuclei directly innervate the posterior pituitary gland, which is responsible for ADH and oxytocin production.

The posterior pituitary gland is a neural structure which has a role in lactation, childbirth and fluid balance. ADH is the hormone which reabsorbs water from the collecting duct of the kidney and levels are kept under close control by serum osmolality and thirst

The most important stimulus for release of hypothalamic oxytocin is initiated by physical stimulation of the nipples or teats. The act of nursing or suckling is relayed within a few milliseconds to the brain via a spinal reflex arc. These signals impinge on oxytocin-secreting neurons, leading to release of oxytocin.