Weitzman R E, Kleeman C R
West J Med. 1979 Nov;131(5):373-400.
Water balance is tightly regulated within a tolerance of less than 1 percent by a physiologic control system located in the hypothalamus. Body water homeostasis is achieved by balancing renal and nonrenal water losses with appropriate water intake. The major stimulus to thirst is increased osmolality of body fluids as perceived by osmoreceptors in the anteroventral hypothalamus. Hypovolemia also has an important effect on thirst which is mediated by arterial baroreceptors and by the renin-angiotensin system. Renal water loss is determined by the circulating level of the antidiuretic hormone, arginine vasopressin (AVP). AVP is synthesized in specialized neurosecretory cells located in the supraoptic and paraventricular nuclei in the hypothalamus and is transported in neurosecretory granules down elongated axons to the posterior pituitary. Depolarization of the neurosecretory neurons results in the exocytosis of the granules and the release of AVP and its carrier protein (neurophysin) into the circulation. AVP is secreted in response to a wide variety of stimuli. Change in body fluid osmolality is the most potent factor affecting AVP secretion, but hypovolemia, the renin-angiotensin system, hypoxia, hypercapnia, hyperthermia and pain also have important effects. Many drugs have been shown to stimulate the release of AVP as well. Small changes in plasma AVP concentration of from 0.5 to 4 muU per ml have major effects on urine osmolality and renal water handling.
位于下丘脑的生理控制系统将水平衡严格调节在小于1%的容差范围内。通过使肾脏和非肾脏的水分流失与适当的水分摄入达到平衡，实现机体水平衡稳态。主要的口渴刺激因素是下丘脑前腹侧的渗透压感受器所感知到的体液渗透压升高。血容量减少对口渴也有重要影响，这是由动脉压力感受器和肾素-血管紧张素系统介导的。肾脏的水分流失由抗利尿激素精氨酸加压素（AVP）的循环水平决定。AVP在下丘脑视上核和室旁核中的特殊神经分泌细胞中合成，并通过神经分泌颗粒沿着伸长的轴突运输到垂体后叶。神经分泌神经元的去极化导致颗粒胞吐，AVP及其载体蛋白（神经垂体素）释放到循环中。AVP会对多种刺激作出分泌反应。体液渗透压的变化是影响AVP分泌的最主要因素，但血容量减少、肾素-血管紧张素系统、缺氧、高碳酸血症、高热和疼痛也有重要影响。许多药物也已被证明可刺激AVP释放。血浆AVP浓度从每毫升0.5到4微单位的微小变化，都会对尿渗透压和肾脏对水的处理产生重大影响。
