Hypothalamic-Pituitary Axis

The hypothalamus and pituitary coordinate endocrine function through a small but highly organized system. The hypothalamus senses neural, metabolic, circadian, and stress signals. It then directs pituitary hormone release, which controls downstream glands such as the thyroid, adrenal cortex, and gonads. The anterior pituitary receives hypothalamic signals through the hypophyseal 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), while somatostatin inhibits GH release. - Dopamine tonically inhibits prolactin. If the pituitary stalk is compressed or damaged, dopamine cannot reach the pituitary effectively and prolactin rises. The posterior pituitary does not synthesize its own hormones. The hypothalamus produces arginine vasopressin (AVP, also called antidiuretic hormone or ADH) and oxytocin; the posterior pituitary stores and releases them. Most pituitary axes operate through negative feedback. Cortisol normally suppresses CRH and ACTH. Thyroid hormones suppress TRH and TSH. This explains a...