HypothalamusHypophysenSystems

The hypothalamus–hypophysis system, often referred to as the hypothalamic–pituitary axis, is the neuroendocrine interface between the brain and the endocrine system. It comprises the hypothalamus and the pituitary gland (hypophysis) and the specialized pathways that connect them, including the hypophyseal portal system and neurosecretory projections.

Anatomy and connections: The hypothalamus is a neuroendocrine control center located in the diencephalon. The pituitary gland sits in the sella turcica and has two components: the anterior lobe (adenohypophysis) derived from oral ectoderm, and the posterior lobe (neurohypophysis) derived from neural tissue. Hypothalamic neurons produce releasing and inhibiting hormones that reach the anterior pituitary via the hypophyseal portal vessels, regulating secretion of trophic hormones. The posterior pituitary stores and releases oxytocin and vasopressin (antidiuretic hormone), which are synthesized in hypothalamic neurons and transported along axons to the posterior lobe.

Functions and regulation: The axis controls growth, metabolism, stress response, reproduction, lactation, and water balance. Anterior pituitary hormones include thyroid-stimulating hormone, adrenocorticotropic hormone, luteinizing hormone, follicle-stimulating hormone, growth hormone, and prolactin. These are regulated by hypothalamic releasing and inhibiting hormones and by negative feedback from target organs and circulating hormones. The system interacts with circadian and autonomic inputs and integrates physiological signals to maintain homeostasis.

Clinical relevance: Disorders include pituitary adenomas causing hormone excess or deficiency, hypopituitarism, and diabetes insipidus from vasopressin disruption. Development and disruption of this axis influence multiple endocrinopathies and are central to endocrine therapeutics.