<prompt> SIADH- all are features except -Decreased sodium, maintaining the concentrating ability of the urine osmolality 100 mOsmNormal sodium balance maintained indicating excess urinary sodium is due to efficient sodium intakeHypouricemiaLow blood pressure due to volume depletion  <response>: The serum sodium concentration is normally regulated by -The balance of water intake.Renal excretion of sodium andADH mediated water conservation by distal renal tubule.These processes are mediated by -Stimulation of thirstSecretion of ADHFeedback mechanisms of the renin angiotensin aldosterone system and variation of renal handling of filtered sodium.Disorders in any one of the these components of sodium balance can result in sodium imbalance.Action of ADHADH is secreted by the posterior pituitary gland. Its effect in kidney is mediated by the vasopressin. V2 receptors on the basolateral surface of the principal cells of the collecting duct. The key action of ADH in the kidney is increasing the permeability of water. It allows water to be reabsorbed from the medullary interstitium thus enhancing water reabsorption.In SIADH the A.D.H. level is inappropriately elevatedThe inappropriately elevated level of vasopressin enhances the reabsorption of water thereby leading to.Production of concentrated urine. Inability to excrete water and consequently Hyponatremia Clinical features of SIADH- Hyponatremie sodium 135 mEqL- Inappropriately elevated urine osmolality 150 mosmkg- Excessive urine sodium excretion Na 30 mEqL- Decreased serum osmolality- 280 mosmkgThese findings occur in- Absence of diuretic therapy- In the presence of euvulemia without edema- In the setting of otherwise normal cardiac, renal, adrenal, hepatic and thyroid function.Remember,. The key to pathophysiological signs, symptoms and eventual treatment of SIADH is an understanding that the hyponatremia is a result of excess water and not a sodium deficiency.Laboratory features of SIADH Hyponatremia sodium 135 mEqLB.U.1V. and serum uric acide tends to fallQ because of plasma dilution and increased excretion of nitrogenous products.Serum potassium and Bicarbonate levels are normal in SIADH hypokalemia and metabolic acidosis suggests, diuretic therapy or vomitingLow serum osmolality.Remember,These characteristic features of SIADHThere is increase in urinary concentration of sodium in the presence of hyponatremia.There is increase in urine osmolarity in the presence of with decrease in serum osmolarity. 