What is the Posterior Pituitary?

The pituitary is a tiny gland located at the base of the brain. It is a projection off of the hypothalamus and is part of the endocrine system. Often called the master gland, the pituitary consists of two lobes: the anterior pituitary lobe, also called the adenohypophysis, and the posterior pituitary lobe, also known as the neurohypophysis. Under the direction of the hypothalamus, the posterior pituitary secretes two hormones that are important in the proper functioning of several bodily systems.

Endocrine hormones are chemicals that travel through the bloodstream carrying messages to different parts of the body. These hormones are produced by an endocrine gland and stimulate action by the targeted cells or organs of the body. Although called a gland, the posterior pituitary, which is part of the endocrine system, is actually a collection of nerve fibers that extend down from the hypothalamus. The hypothalamus is responsible for regulating things such as hunger, thirst, body temperature, and blood pressure. It synthesizes many different hormones, and either the anterior pituitary or the posterior pituitary stores and releases these hormones into the bloodstream.

The two hormones that the posterior pituitary secretes are oxytocin and antidiuretic hormone (ADH), or vasopressin. Oxytocin stimulates uterine contractions when a mother gives birth; doctors often give it to pregnant women to induce labor contractions. It also causes the release of milk when a baby begins to nurse. Many researchers believe oxytocin helps in the bonding process between mates or between mother and child, and that it may cause increased feelings of trust, generosity, and contentment.

ADH works on the ducts in the kidneys to enhance the reabsorption of water into the blood, thereby causing less urine to be formed. When the body does not produce enough ADH, a condition known as diabetes insipidus can result. Diabetes insipidus causes the body to excrete large amounts of urine, which can cause severe dehydration and even death. Symptoms of the disease include extreme thirst, excessive urination, dehydration, fever, vomiting, and diarrhea.

Causes of diabetes insipidus include a malfunctioning hypothalamus that produces not enough ADH, or a malfunctioning posterior pituitary that fails to release enough ADH. These malfunctions can have many causes. Some of the most common include brain injury, tumors, encephalitis, meningitis, blood clots, drugs, and injuries or disease affecting the kidney's ability to react to ADH.

Treatments for diabetes insipidus will depend on the underlying cause of the disease. Typically, treating the cause will treat or lessen the effects of the diabetes. Without treatment, diabetes insipidus can lead to brain damage, hyperactivity, mental impairment, and other nervous system disorders.