Hypopituitarism refers to a disorder of the pituitary gland in which it secretes one or more of its hormones in deficient amounts to the blood circulation. Panhypopituitarism refers also to a disorder of the pituitary gland in which there is deficiency of all its hormones in the blood. The pituitary gland is an extremely important structure in the body. It is an organ which has rich blood supply in order to nourish its metabolically active cells.
The pituitary gland secretes several hormones from two anatomically distinct parts of its structure. These hormones regulate all aspects of metabolism in the body that range from cellular growth to reproduction. The pituitary gland is the master gland of the body due to its controlling function of other endocrine organs in the body. It is only controlled by a structure in the brain which is called the hypothalamus.
This structure secretes several hormones each is specific for a different hormone that is secreted by the pituitary gland. Hormones of the pituitary gland are usually under the positive feedback effect of appropriate hormones in the hypothalamus. This means that increased secretion of a hormone by the hypothalamus leads to an increase in the secretion of its counterpart hormone in the pituitary gland.
This rule applies to all hormones of the pituitary gland except one hormone which is called prolactin. This hormone is secreted by a specialized type of cells in the anterior pituitary gland which are called lactotrophs. This hormone contrary to other hormones of the anterior pituitary gland is regulated by a negative feedback control frm a hormone that is secreted by the hypothalamus and which is called dopamine. Increased secretion of dopamine by the hypothalamus leads to a decrease in the secretion of prolactin by the pituitary gland and vice versa. Prolactin is a polypeptide hormone that induces lactation or the secretion of milk from the breast of the mother during infant feeding.
Hormones of the anterior pituitary gland control other endocrine glands in the body such as the adrenal gland and the gonads in addition to the thyroid gland. Usually the feedback control of hormones secretion by the pituitary gland is tightly regulated by the positive feedback effect of the hormones from the hypothalamus and by the negative feedback inhibition of the hormones by the endocrine glands in the body which are under direct control by hormones of the pituitary gland.
As an example, the adrenocorticotropic hormone (ACTH) which is secreted by specialized cells in the anterior pituitary gland which are called corticotrophs is under the positive fedback effect of the hormone corticotropin releasing hormone which is secreted by the hypothalamus. Also ACTH is under the negative feedback control of the hormone cortisol which is secreted by the adrenal cortex.
The balance between the secretion of these hormones is manifested by the excess of cortisol in the blood as occurs in cushing syndrome in which the adrenal gland secretes cortisol to the blood in excessive amounts. As a result a negative feedback inhibition leads to the decreased secretion of ACTH by the anterior pituitray gland. Also the opposite effect is seen with addison’s disease in which the secretion of cortisol by the adrenal cortex is impaired due to an autoimmune destruction of the adrenal cells. As a result of the deficiency of cortisol in the blood the negative feedback inhibition is lifted and more ACTH is secreted by the pituitary gland to the blood circulation.
Also a defect in the cells of the pituitary gland which are specialized in the secretion of ACTH leads to the deficiency of ACTH in the blood. As a result also the adrenal gland secretes less of the cortisol hormone to the blood. The afore mentioned discussion of negative feedback applies to other endocrine glands in the body such as the gonads in both the males and the females. In addition it also applies to secretion of hormones by the thyroid gland