Pituitary Gland Health Article

Role in human health

Hormones released from the anterior and posterior pituitary have far-reaching effects on many different organ systems and physiological processes.

Hormones of the anterior pituitary

Luteinizing hormone and follicle stimulating hormone are called gonadotropins. As the name suggests, the target tissues of these hormones are the gonads (ovaries and testes). They have two main functions. The first is to promote the development and maturation of sperm and eggs. Second, they stimulate the production and release of such sex steroid hormones as estradiol and testosterone in women and men respectively.

Prolactin is responsible for stimulating cells in the female breast to produce milk. Therefore, lactotrophs located in the anterior pituitary of women that are breast-feeding are large and numerous, indicating an increased amount of prolactin production. These lactotrophs comprise about 30% of the cells in the anterior pituitary. The pituitary in women doubles in size during pregnancy because of the increase in size and number of lactotrophs.

The target tissue of adrenocorticotropic hormone is the adrenal cortex (part of the adrenal gland that is located above the kidney). ACTH stimulates the production of cortisol and also causes the cells of the adrenal gland to grow. Cortisol has many effects on metabolism in various tissues.

Growth hormones have many different target tissues and promote the growth of each of them. For this reason human growth hormone (GH) is considered an anabolic hormone, indicating that it is responsible for building tissue proteins. For example, GH directly increases protein synthesis in muscles and the liver; and it decreases the size of adipose tissue. It also has an indirect effect by stimulating other hormones. Growth hormones indirectly affect the bones by increasing protein synthesis, collagen synthesis and cell proliferation. In many other tissues, the indirect effects of growth hormone are responsible for protein, RNA and DNA synthesis. The overall effect of growth hormone is to promote skeletal growth and a lean body mass.

As its name implies, thyroid-stimulating hormone (TSH) promotes cell growth in the thyroid gland. TSH also triggers the secretion of thyroid hormones that affect many metabolic processes in the body.

Hormones of the posterior pituitary

Both oxytocin and antidiuretic hormone (ADH) are peptide hormones that are synthesized in the cell bodies of the nerves originating in the hypothalamus and then delivered through the axons to the posterior pituitary. Thus, they are good examples of neuroendocrine hormones.

The primary target organ of ADH is the kidney. ADH is responsible for increasing water retention by the kidney, resulting in an increase in extracellular fluid and a decrease in urine volume. Receptors in the hypothalamus called osmoreceptors can sense the concentration of water in the extracellular fluid through changes in extracellular fluid osmolarity. The osmoreceptors in turn determine the release of ADH by the posterior pituitary. The consumption of alcohol decreases the amount of ADH released. As a result, more fluid is lost through urination, resulting in excessive water loss and thirst.

The primary site of action of oxytocin is female breast tissue. Oxytocin stimulates the contraction of smooth muscle cells in the breast, transferring milk from the place of synthesis to the larger ducts of the breast. Oxytocin is secreted by the stimulation of touch sensors when an infant is suckling. Other psychological factors, such as the sound of a baby crying, can stimulate the release and action of oxytocin. The role of oxytocin in the onset of labor contractions is not fully clear. There is no known stimulus for the secretion of oxytocin in the human male.

Hypopituitarism

Disorders of the pituitary gland can have severe effects on normal growth and sexual maturation. A general condition known as hypopituitarism, also known as pituitary dwarfism, is characterized by a decrease in one or more of the hormones produced by the anterior pituitary. Sexual immaturity and metabolic dysfunction leading to obesity are symptoms of this syndrome. When hypopituitarism occurs in childhood, growth is slowed. Tumors are often the cause of hypopituitarism; however, sometimes there is no identifiable cause. If there is a decrease in the levels of hormones released from the hypothalamus, then hypopituitarism results. The symptoms vary according to the number and amount of hormones that are deficient. The most effective treatment is the administration of replacement hormones.