The pituitary gland is a small endocrine gland that is located at the bottom aspect of the brain, below the hypothalamus. Despite its small size it is of paramount importance due to the hormonal control that it exerts on other endocrine glands in the body. It is considered to be the master endocrine gland of the body.
It secretes several hormones that function by regulating the physiology of other endocrine glands, such as the gonads and the thyroid. The function of the pituitary gland is tightly regulated by hormones that are secreted from the hypothalamus. Most hormones of the pituitary gland are regulated by a positive feedback from hormones in the hypothalamus, except for the hormone prolactin, which is regulated by a negative feedback from the hormone dopamine also secreted by the hypothalamus.
Pituitary gland insufficiency can have several causes. Some of them are typical of the pituitary itself and others are caused by dysfunction of the hypothalamus. Due to its function in secreting many hormones, pituitary hypofunction can be due to a deficiency in the secretion of one of its hormones or many hormones.
In the case of a complete hypofunction of the gland and which includes insufficiency in the secretion of all hormones this condition is called panhypopituitarism. The pituitary gland is divided into an anterior part and a posterior part, both of which can be a target for hypofunction.
There is one hormone that is secreted by the posterior pituitary gland and which is called antidiuretic hormone. This hormone has distinct clinical significance in its excess in the blood as well as in its deficiency. In hypofunction of the pituitary gland in its posterior part the lack of the antidiuretic hormone leads to excessive secretion of water in the urine. This leads in turn to polyurea and a sensation of thirst.
Hypofunction of the pituitary gland can be caused due to several reasons. It can be caused by several systemic diseases such as occurs in sarcoidosis and hemochromatosis. In addition it occurs in histiocytosis. A trauma to the brain can precipitate a damage to the anterior pituitary gland in which some or all of the hormones can be deficient from its secretion.
Trauma to the posterior part of the gland can render a deficiency in the hormone antidiuretic hormone with subsequent development of diabetes insipidus. Immunologic diseases can also cause dysfunction of the pituitary gland. Another cause to hypopituitarism is a surgery to remove an adenoma. The removal of part of the gland can make it hypofunctional.
Radiotherapy to the brain region that is adjacent to the pituitary gland or the hypothalamus can affect the gland by destroying its tissue. Thus this makes it hypofunctional and deficient in the hormone secretion. Other causes of pituitary gland insufficiency include diseases of infectious origin that can affect the pituitary gland. Examples of such a diseases include tuberculosis and syphilis.
In addition, fungal infections have been found to affect the function of the pituitary gland. This can also cause Idiopathic disorders of the pituitary gland. Isolated deficiency of the various hormones from the pituitary gland are also known to occur. Growth hormone deficiency can cause distinct clinical symptoms such as dwarfism and growth retardation.
Adrenocrticotropic hormone deficiency is a rare incidence and is clinically manifested as adrenal cortical insufficiency with cortisol deficiency and Addison's symptoms. Prolactin hormone deficiency implies severe damage to the pituitary gland. In addition with a deficiency of this hormone a state of panhypopituitarism is usually present.