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Discuss the structure and function of the pituitary gland, with special emphasis on the hormones released from the posterior pituitary.

The pituitary gland is attached to the brain by the infundibulum. This structure is a stalk with two important components: 1) nerves whose cell bodies are located within the hypothalamus and 2) a capillary bed that has already passed through the hypothalamus. Both of these structures are integral to the function of the pituitary gland. The pituitary gland can be divided into an anterior portion ( adenohypophysis) and a posterior portion ( neurohypophysis). The posterior portion contains the nerve endings that originate within the hypothalamus. The two peptide hormones released from the posterior pituitary are antidiuretic hormone (ADH or vasopressin) and oxytocin. ADH is synthesized in the paraventricular nucleus of the hypothalamus, while oxytocin is synthesized in the supraoptic nucleus of the hypothalamus. Following their synthesis, ADH and oxytocin are packaged into vesicles within the [[Golgi apparatus[[ and transported along the nerves within the infundibulum to the posterior pituitary, from which they are released. Both ADH and oxytocin are considered neurohormones because they are released from nerve terminals. ADH alters water reabsorption in the kidneys, whereas oxytocin functions in uterine contraction and milk let-down in the breast. The hypothalamic-pituitary portal system describes the capillary bed that first drains the hypothalamus. The cells of the hypothalamus release tropic hormones into the bloodstream. Those tropic hormones diffuse from the second capillary bed to the cells of the anterior pituitary. The endocrine cells of the anterior pituitary are stimulated to increase or decrease their release of hormones into the bloodstream.