neurohypofysiin

Neurohypophysis, also known as the posterior pituitary (Finnish: neurohypofysiin), is the part of the pituitary gland that stores and releases two hypothalamic hormones: vasopressin (antidiuretic hormone, ADH) and oxytocin. These hormones are synthesized in magnocellular neurons of the hypothalamus and transported along axons to the posterior pituitary, where they are stored in nerve terminals and released into the bloodstream in response to neural signals.

Anatomy and connections: The posterior pituitary consists of the pars nervosa and infundibulum. It is neural tissue, connected to the hypothalamus by the hypothalamo-neurohypophyseal tract rather than a portal circulation. Hormones enter a capillary network from which they reach systemic blood.

Functions: Vasopressin promotes water reabsorption in the kidneys, concentrating urine and regulating body fluid osmolality; oxytocin stimulates uterine contractions during parturition and milk ejection in lactation. Additional roles in social behavior and maternal bonding have been described.

Regulation: Osmoreceptors in the hypothalamus sense plasma osmolality and influence ADH release; changes in blood volume and pressure also modulate secretion. Oxytocin release is primarily stimulus-driven (labor, suckling) but can be affected by social cues and feedback.

Clinical relevance: Deficiency of ADH due to damage to the hypothalamus or posterior pituitary causes central diabetes insipidus, with polyuria and polydipsia. Excess ADH secretion leads to SIADH and hyponatremia. Lesions from tumors or trauma can impair neurohypophyseal function.