Hypothalamic-Pituitary Axis

The hypothalamus and pituitary function as a linked control center. The hypothalamus senses neural input, stress, sleep, temperature, circulating hormone levels, and fluid balance. It then directs pituitary hormone secretion. A lesion at any point in this system can affect thyroid function, adrenal function, reproduction, growth, lactation, and water balance. The anterior pituitary is controlled through the hypothalamic-pituitary portal circulation: - Corticotropin-releasing hormone stimulates adrenocorticotropic hormone (ACTH), which stimulates cortisol production. - Thyrotropin-releasing hormone stimulates thyroid-stimulating hormone (TSH), which stimulates thyroid hormone production. - Gonadotropin-releasing hormone stimulates luteinizing hormone (LH) and follicle-stimulating hormone (FSH), which regulate gonadal hormone production and fertility. - Growth hormone-releasing hormone stimulates growth hormone (GH); somatostatin inhibits GH secretion. - Dopamine continuously suppresses prolactin secretion. The posterior pituitary does not synthesize its own hormones. The hypothalamus produces arginine vasopressin (AVP), also called antidiuretic hormone (ADH), and oxytocin. These hormones travel down axons to the posterior pituitary, where they are stored and released. This anatomy explains a useful localization clue. A lesion of the pituitary stalk may interrupt hypothalamic dopamine delivery. Without dopamine’s inhibition, prolactin rises. At...