This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Medicine
[{'content': 'SIADH- all are features except - \nSelect and explain. \nA. Decreased sodium, maintaining the concentrating ability of the urine osmolality (> 100 mOsm), B. Normal sodium balance maintained indicating excess urinary sodium is due to efficient sodium intake, C. Hypouricemia, D. Low blood pressure due to volume depletion', 'role': 'user'}, {'content': 'Answer: D \nExplanation: The serum sodium concentration is normally regulated by -\n\nThe balance of water intake.\nRenal excretion of sodium and\nADH mediated water conservation by distal renal tubule.\n\nThese processes are mediated by -\n\nStimulation of thirst\nSecretion of ADH\nFeedback mechanisms of the renin angiotensin aldosterone system and variation of renal handling of filtered sodium.\n\nDisorders in any one of the these components of sodium balance can result in sodium imbalance.\nAction of ADH\n\nADH is secreted by the posterior pituitary gland. \nIts effect in kidney is mediated by the vasopressin. (V2 receptors) on the basolateral surface of the principal cells of the collecting duct. \nThe 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.\n\nIn SIADH the A.D.H. level is inappropriately elevated\n\nThe inappropriately elevated level of vasopressin enhances the reabsorption of water thereby leading to.\nProduction of concentrated urine.\n\xa0Inability to excrete water and consequently\n\xa0Hyponatremia\xa0\n\n\u200b\u200bClinical features of SIADH\n- Hyponatremie (sodium < 135 mEq/L)\n- Inappropriately elevated urine osmolality\xa0(> 150 mosm/kg)\n- Excessive urine sodium excretion ( Na > 30 mEq/L)\n- Decreased serum osmolality- (< 280 mosm/kg)\nThese findings occur in\n- Absence of diuretic therapy\n- In the presence of euvulemia without edema\n-\xa0In the setting of otherwise normal cardiac, renal, adrenal, hepatic and thyroid function.\nRemember,\n. 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.\nLaboratory features of SIADH\n\xa0\n\nHyponatremia (sodium < 135 mEq/L)\nB.U.1V. and serum uric acide tends to fallQ because of plasma dilution and increased excretion of nitrogenous products.\nSerum potassium and Bicarbonate levels are normal in SIADH (hypokalemia and metabolic acidosis suggests, diuretic therapy or vomiting)\nLow serum osmolality.\n\n\u200bRemember,\nThese characteristic features of SIADH\n\nThere is increase in urinary concentration of sodium in the presence of hyponatremia.\nThere is increase in urine osmolarity in the presence of with decrease in serum osmolarity.', 'role': 'assistant'}]