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ADH Secrelion and Actiol

RENAL PHYSIOLOGY

MtCHANISM OF ANT1DIURETIC HORMONE IN REGUŁ ATINC URINE VOLUME AND CONCENTRAIION

ADH ii produced in iupraoptic and paraventricu lar nuclci of hypolhalamus and descends along nprvo fibers to njHirohypophysis, where it i* itorcd

Hlood o$rm>lalilv and volume modified by Fluid intake (mai 01 parenterall; water and eleclrołyle r*xchanee with tissues. norma! or uathokiuiral

ADH cauics walls of collecting ducb to become morę peimedble to water and rhus permits os-molar eąuilibralion and ahsorption of water into the hypertonic interstitium, a smali volume of bighły Loncentrated urine is ekcrcled

In presenre ot ADH, blood flow to renal meduHa i$ diminbhed, thtis augmenting hypcrtonicily of meduUary interstitium by minimiz-ing depłption of solutes via bloocł-

blood osmolality affecting hypolhalamic osmore-ceptore and by Iow -hlood volume arfceting thoracic and carotid yolume receptors; Iow osmolality and high blood volumc inhibit ADII release

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Plasmn osmolality (mOsm/kg t-hOl

Figurę 6.9 ADH Secretion and Action

ADH regulates the volume t>ł water excreted by the kidneys. Its secretion is restulated by the osmolality of the borly fluids and the blood volume ancł pressure. Changes in body fluid osmolality of a few porc.cnt are sufficient to signiticantly alter ADH secretion. Decreases in blood volume and pressure ot 10% to 15% or morę are needed to effect ADH secretion. The blood volume and pressuri sensors are found in the large pulmonary ves$els, the carotid sinu*> and the aortic arch. Thcse "barorccepiors" respond to stretch ot th-: vesscl wali, which in tum is dependent on blood volume and pres-

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