hypothalamuspituitary

The hypothalamus-pituitary axis is a central neuroendocrine system that coordinates most of the body’s endocrine activity. The hypothalamus communicates with the anterior pituitary via a portal venous system that delivers releasing and inhibiting hormones, directing the secretion of pituitary hormones. The posterior pituitary stores and releases neurohormones produced in the hypothalamus, which are transported along axons to the posterior lobe.

The anterior pituitary secretes hormones that control other glands and tissues: adrenocorticotropic hormone (ACTH) targets the adrenal cortex; thyroid-stimulating hormone (TSH) targets the thyroid; luteinizing hormone (LH) and follicle-stimulating hormone (FSH) target the gonads; growth hormone (GH) acts on various tissues; and prolactin (PRL) targets the mammary gland. Hypothalamic releasing and inhibitory hormones regulate these secretions: gonadotropin-releasing hormone (GnRH), thyrotropin-releasing hormone (TRH), corticotropin-releasing hormone (CRH), growth hormone-releasing hormone (GHRH), somatostatin, and dopamine (which inhibits prolactin). The pituitary outputs are modulated by feedback from peripheral hormones, establishing negative feedback loops that maintain homeostasis.

The posterior pituitary secretes vasopressin (antidiuretic hormone, ADH) and oxytocin. These hormones are synthesized in the hypothalamus and released from the posterior lobe; ADH regulates water reabsorption in the kidneys, while oxytocin influences labor, lactation, and certain social behaviors.

Dysfunction of the axis can lead to central diabetes insipidus, pituitary adenomas, or hypopituitarism, with downstream effects on thyroid, adrenal, reproductive, and metabolic systems. Diagnosis combines hormone assays and imaging, guiding targeted treatment.