The Posterior Pituitary: ADH and Oxytocin

Key points

• • The posterior pituitary does not make hormones itself; it stores and releases two hormones made by nerve cells in the hypothalamus and carried down their axons.
• • Antidiuretic hormone (ADH, also called vasopressin) makes the kidney reabsorb water, concentrating the urine and saving body water.
• • ADH is released when the blood becomes too concentrated or the blood volume falls, and it also narrows blood vessels to help support the blood pressure.
• • Too little ADH (or a kidney that cannot respond to it) causes diabetes insipidus, with the passing of large amounts of dilute urine and great thirst.
• • Oxytocin causes the womb to contract in labour and the breast to release milk when the baby suckles, in a positive-feedback loop.
• • Both hormones are released by nerve signals, which is why suckling or the stretch of the birth canal can trigger their release.