Pituitary Disorders

Pituitary 101

The pituitary gland is often considered the “master gland” because it regulates most of the body’s hormonal balance. The gland itself is regulated by the brain through hormones that travel through the infundibulum and the pituitary stalk. The adult pituitary gland measures 12 x 6 x 9 mm and weighs 0.6 gram. It enlarges during pregnancy, when it may weigh 1 gram or more. It is located in the center of the head, at the base of the brain, behind the eyes, below the optic nerves, resting in the sella turcica (Turkish saddle), which is located in the back of the sphenoid sinus. The normal gland is shaped like a kidney bean and measures only 8-12 mm in size (less than 1 inch in diameter), but controls secretion of many of the hormones that regulate essential body processes. The gland is separated into the anterior lobe (adenohypophysis) and the much smaller posterior lobe (neurohypophysis). Adjacent to the gland on both sides rests the cavernous sinus, a venous channel containing the carotid artery and nerves that move the eyes. The optic nerves are suspended 4-8 mm above the gland.

The adenohypophysis constitutes approximately 80% of the entire pituitary gland and is divided intothree parts called the pars distalis, pars intermedia, and pars tuberalis. The pars distalis is the largestand the functional part of the adenohypophysis. The pars intermedia in the human pituitary is a poorlydeveloped, rudimentary structure lying between the anterior and posterior lobes. It often degeneratesnto a pars intermedia cyst (< 5 mm) filled with colloid material. The pars tuberalis is an upward
extension of the adenohypophysis along the pituitary stalk and may be a source of suprasellarpituitary adenomas. The anterior lobe is the source of prolactin, growth hormone, thyroid-stimulating hormone, gonadotropic hormones (FSH and LH), and adrenocorticotropic hormone (ACTH).The neurohypophysis is a funnel-shaped structure with the base forming the pituitary stalk and ending in the posterior lobe with the pituitary fossa. The neurohypophysis is made of axonal endings containing neurosecretory vesicles (storing the hormones oxytocin and anti-diuretic hormone) and pituicytes (the cell-type specific to the posterior lobe of the pituitary). The axons originate from the hypothalamus, where the hormones are produced.