The pituitary gland is a small yet very important endocrine gland which lies at the bottom aspect of the brain. It lies immediately below the hypothalamus and there is a connection between the hypothalamus and the pituitary gland which is called the pituitary stalk. In spite of its small size the pituitary gland is a key structure that its damage can be manifested clinically by many symptoms that depend on the site of injury to the gland. It is considered the master gland of the body due to its important functions.
The pituitary gland is divided into two physiologically distinct strucutures. These are the anterior pituitary gland or adenohypophysis and the posterior pituitary gland or neurohypophysis. These two structures secrete different types of hormones to the blood circulation. All of the hormones that are secreted by the pituitary gland are protein hormones that are synthesized and secreted by the pituitary gland.
Hormones of the posterior pituitary gland are partly synthesized in the hypothalamus and are stored in the posterior pituitary gland. All hormones of the anterior pituitary gland are regulated by a positive feedback from hormones that are secreted by the hypothalamus except one hormone which is regulated by a negative feedback from the hormone dopamine. This hormone is called prolactin.
Hormones of the pituitary gland function by regulating the secretions of other endocrine glands in the body. This is true for all pituitary hormones except for the hormone growth hormone. This hormone does not have a specific target organ to act upon. Instead its action is universal on all body cells causing general promotion of body growth by increasing cellular metabolism.
Disorders which involve this hormone can have drastic manifestations on the child development. Its deficiency can cause dwarfism while its excess can cause the person to develop tall body. Also growth hormone excess in the blood can cause diabetes symptoms in affected individuals due to its effect on glucose level in the blood. High level of growth hormone in the blood leads to hyperglycemia. Growth hormone is under the negative feedback control from the hormone growth hormone inhibiting hormone.
In addition to growth hormone which is secreted by the anterior pituitary gland also other five hormones are secreted by the same gland in its anterior aspect. The first of them is the thyroid stimulating hormone. This hormone acts on the thyroid gland and stimulates the synthesis and release of the thyroid hormone.
Thyroid stimulating hormone is under positive feedback control from a hormone that is secreted by the hypothalamus and which is called thyrotropin releasing hormone. High concentration of thyroid stimulating hormone in the blood can signify a pathology of the thyroid gland in which it secretes thyroid hormone in deficient quantity to the blood circulation. Also decreased amount of thyroid stimulating hormone in the blood signifies a hyperfunctional thyroid gland which oversecretes the thyroid hormone.
The other hormone that is secreted by the anterior pituitary gland is adrenocorticotropic hormone (ACTH). This hormone regulates the level of cortisol in the blood. Its deficiency in the blood can cause adrenal insufficiency with hypocortisolism. While the excess of ACTH can cause adrenal hyperfunction. This disorder is often called cushing disease to differentiate it from cushing syndrome which is hypercortisolism due to a defect in the adrenal cortex.
ACTH is under the positive feddback control from the hormone corticotropin releasing hormone that is secreted by cells of the hypothalamus. ACTH is under negative feedback control from the hormone cortisol.
The other two hormones that are secreted by the anterior pituitary gland are follicle stimulating hormone (FSH) and luteinizing hormone (LH). Both of these hormones play different role in their effect on sexual organs in males as well as females. In the male LH stimulates the release of testosterone from the testes while FSH stimulates sparmatogenesis.
In the femal, both of these hormones act synergistically to control the function of the ovaries. They promote the secretion of estrogens and progesterone by the ovaries and the corpus luteum. In addition they stimulate the maturation of the follicles in the ovaries.
The posterior pituitary gland secrete two hormones. These are: ADH and oxytocin. Oxytocin stimulates the contraction of breast muscles in females in order to release milk. In addition, it functions by stimulating the contraction of the uterine muscle during child birth. ADH is the hormone which is responsible for water homeostasis in the body.
