The pituitary gland is one of the endocrine glands. The pituitary hangs from the bottom of the brain by a little stalk just above the nasal passage. See figure below. Because of its many hormones which are vitally concerned in fundamental physiological functions, it is sometimes designated as the master gland. It is about the size of an acorn. The pituitary is actually two glands in one, the posterior and anterior. Of the two, the posterior pituitary manufactures no hormones of its own, but stores two hormones that are initially secreted in a part of the brain known as the hypothalamus. The hormones are oxytocin, which is believed to stimulate labor at the end of pregnancy, and vasopressin, which helps the body retains its fluids.
The anterior pituitary controls the overall growth of the body. The anterior lobe originates embryonically from the epithelial lining of the pharynx. The anterior portion has many functions and several of its hormones have been isolated.
(figure available in print form)
The growth hormone, sometimes called somatotropin, regulates the growth of bone, muscle, and other tissues from top to toe. In some individuals, fortunately only a few, underproduction or over-production of somatotropin occurs during childhood. Either extreme causes growth abnormalities. Excessive production can result in gigantism or acromegaly; decreased production is responsible for certain types of dwarfism. The pituitary dwarf almost never attains adult proportions or sexual maturity, although his or her I.Q. is normal.
In the average person the anterior pituitary hormones are of great concern because it regulates other endocrines.
The gonadotropic or follicle-stimulating, FSH and luteinizing hormones, LH, are intimately connected with ovarian function and menstruation. In the male, the follicle-stimulating hormone induces the development of spermatozoa in the testicle while the luteinizing hormone stimulates the production of the male sex hormone, testosterone.
The lactogenic hormone prolactin is necessary for the initiation of the flow of milk and normal laction following pregnancy.
The adrenocorticotropic hormone, ACTH, promotes hydrocortisone production in the presence of stress. (i.e. Punch on the nose or fever or worry) Hydrocortisone raises blood sugar (for healing process) and acts as an anti-inflammatory.
The thyrotropic or TSH, signals the thyroid to manufacture thyroxine when the level gets too low. Without thyrotropic hormone, thyroid gland undergoes atrophy; in the presence of excess, the thyroid increases in glandular tissue and function.
Endocrine control works both ways. Just as a thermostat, which fires a furnace into activity when the room temperature drops, is itself turned off when the temperature rises high enough, the production of each of the stimulating hormones in the pituitary is suppressed by the presence in the blood of the hormone which it stimulated. Thus, as the level of thyroxine drops, TSH is poured out to goad the thyroid cells into activity; but as soon as production has been speeded up, the very presence of thyroid hormone in quantity in the bloodstream blocks the pituitary’s release of more TSH until thyroid activity slows down again. The result of this cycle is the maintenance of a remarkably steady balance of thyroid hormone in the bloodstream at all times. Such a feedback system serves to regulate the levels of adrenal hormones and sex hormones in much the same way.