Anatomy and Physiology of the Hypothalamic-Piuitary Axis

Abstract

The pituitary gland is a small gland located in the sella turcica, a cavity in the base of the brain. The pituitary gland measures less than 1 cm and weighs less than 1 g but is responsible for maintaining critical homeostatic functions that sustain life. Almost all of the functions of the pituitary are regulated by input from the hypothalamus, and the two glands are connected through the hypophyseal (pituitary) stalk. The pituitary has 3 lobes—anterior (adenophyophysis), posterior (neurohypophysis), and intermediate (pars intermedia) lobe. The anterior, intermediate, and posterior sections of the pituitary act synergistically and are independently functional, each section producing different hormones and regulatory processes. The anterior pituitary produces six hormones in peptide form, including thyroid stimulating hormone (TSH), corticotropin or adrenocorticotrophic hormone (ACTH), follicle stimulating hormone (FSH), lutenizing hormone (LH), growth hormone (GH), and prolactin (PRL). All of the anterior pituitary hormones except PRL act by stimulating other glands to release additional hormones. The release and production of these hormones is controlled through a classic feedback loop. The posterior lobe of the pituitary, also known as the neurohypophysis, secretes oxytocin and anti-diuretic hormone (ADH), also known as vasopressin. Release of the posterior pituitary hormones is regulated by neuronal activity.

Disruption to the pituitary gland may cause dysregulation to hormone production or secretion. The etiology of dysregulation is varied but the majority of dysfunction is related to the presence of a pituitary tumor or adenoma. However, hypopituitarism may be congenital, caused by an unrelated illness, injury and in some cases is the result of treatment for other diseases. Patients may present with a wide range of pathophysiologic symptoms, including bone growth disruption, infertility, galactorrhea, muscle wasting, headaches, fatigue, poor blood pressure homeostasis, or disruption to normal fluid balance. Patients with pituitary diseases often require lifelong treatment and require intense education regarding their disease and treatment, management of comorbidities and psychological support.

Advances in medicine now allow replacement of all pituitary deficiencies so that patients, even with panhypopituitarism, have the potential to lead a full and productive life. Early detection and appropriate medical therapies for all pituitary dysfunctions are critical.