Location
The pituitary gland is located in the center of the skull, just behind the bridge of the nose.
It is about the size of a pea and is a very important link between the endocrine and
nervous systems. The pituitary gland is split into two halves, the anterior and posterior.
The posterior pituitary releases 2 main hormones that affect sexual development and
urinary homeostasis. The pituitary gland was once believed to be the “master gland” of
the body. It is now known that the link between the pituitary gland and the brain, the
hypothalamus, is the master gland. The hypothalamus receives nerve impulses to activate
the pituitary to produce the necessary hormones. Some of these hormones are produced
specifically for the “fight or flight” response, a part of the sympathetic nervous system.
Hormones
.The hormones released by the posterior pituitary gland are actually synthesized by the
hypothalamus. They migrate along nerve fibers to the posterior pituitary gland and are
stored until stimulated to be released into general circulation. There are two main
hormones produced and released by the posterior pituitary gland, oxytocin and
vasopressin (also known as antidiuretic hormone or ADH). Oxytocin, is responsible for
the contraction of the smooth muscles of the uterus and the myoepithelial cells lining the
duct of the mammary gland. In males, oxytocin stimulates the smooth muscle
contraction in the walls of the prostate gland. Oxytocin is also important for child birth,
as it causes the myometrium to contract, which helps constrict the blood vessels that are
sending blood to the uterus at the time of childbirth at a rate of a liter per minute. There
are no known diseases due to over- or underproduction of oxytocin.
Vasopressin (ADH) plays a key role in maintaining a constant total volume of water in
the kidneys. ADH also causes the constriction of peripheral blood vessels, which helps to
increase blood pressure. Underproduction of ADH results in diabetes insipidus. This
condition makes an individual thirsty all the time, but the fluids aren’t stored. Treatment
of this condition is with analogues of ADH such as desamino D-arginine taken
subcutaneiously or by nasal spray. Overproduction of ADH results in water retention,
hyponatraemia, and high urine osmolality. It can be fatal in extreme cases.
Problems of the Posterior Pituitary Gland
There are few but significant problems that can affect the Posterior Pituitary Gland. Many
of the problems that can occur with an abnormally functioning pituitary are diseases that
are more common than one may suspect. Diabetes Insipidus, the disease causing the
most concern among the body’s endocrine system can be shown through two major
symptoms. First, Polyuria; is when the patient passes large amounts of diluted urine.
Polydipsia, is usually followed or closely related to the patient’s excessive thirst. There
are not many treatments for this disease, other than consumption of large quantities of
water and frequent restroom stops. (Diabetes Insipidus is not to be confused with a more
common type of diabetes in which Insulin levels must be carefully monitored. Secondly,
a disease known as “Dilutional Hyponatremia” or “Syndrome of Inappropriate
Antidiuretic Hormone (SIADH)” is a result of too much VP being produced. When
trauma affects portions of the brain, or when a patient is affected with certain types of
cancers, this disease may become evident. The person will begin production of
extremely concentrated urine, and could possible experience vomiting, nausea, seizing
and even death. This disease also affects the levels of Sodium in the bloodstream and an
injection of the ion may be needed if the levels become too low. The pituitary gland is a
small portion of the brain; however its influence encompasses a large part of our body
and our well-being.
Functions
The Posterior Pituitary gland serves as a hub for major aspects of brain, hormone, and
body control. The primary function of the pituitary is the secretion of hormones. The
posterior pituitary gland contains two hypothalamic neurons. One manufactures the
hormone ADH, and the other manufactures Oxytocin. Oxytocin, most evident during
birth, stimulates the contractions of the uterus and stimulates the milk glands to release
milk shortly after birth. This phenomenon is an indication as to the reason why some
Obstetricians will inject this hormone during the birthing process in an effort to smooth
the process. However, if a woman is abnormally low or high in levels of Oxytocin, the
event will not be particularly dangerous to the woman. In men, Oxytocin regulates the
smooth muscle contraction in the walls of the pituitary gland. The Antidiuretic Hormone
(ADH) is what is released when the body responds to a change in concentration of
electrolytes in the blood. It is a part of the body’s own natural buffering system which is
designed to maintain homeostasis throughout the bloodstream. The products produced by
these hypothalamic neurons are transported through axons along the indifibulum. (The
connection of the Pituitary gland and the hypothalamus.) The function of the posterior is
extremely specific compared to that of the Anterior Pituitary. It is truly amazing how
such a small part of the brain can be so crucial to our mere survival.