The pituitary gland contains two lobes - the posterior and anterior pituitary. The posterior pituitary stores and secretes two important hormones - oxytocin and antidiuretic hormone (ADH), which are synthesized by the hypothalamus. ADH increases water reabsorption in the kidneys to concentrate urine, and also causes vasoconstriction. Oxytocin causes uterine contractions and milk ejection during breastfeeding. Disorders can result from too much or too little of these hormones.