Chemical Coordination And Integration

Hormonal control of water balance is exerted partly by the posterior pituitary. NCERT Class 11, Chapter 22 (Chemical Coordination and Integration) describes antidiuretic hormone, also called vasopressin, which acts on the kidney tubules to promote reabsorption of water and reduce urine volume. When its secretion is deficient, water reabsorption falls and the body excretes large quantities of dilute urine, the hallmark of diabetes insipidus. Insulin is incorrect; it is a pancreatic hormone lowering blood glucose, and its deficiency causes diabetes mellitus characterised by raised blood sugar, not dilute urine from a water-balance defect. Thyroxine is wrong because it is a thyroid hormone regulating basal metabolic rate, growth and development, with no primary role in renal water conservation. Glucagon is also incorrect; secreted by pancreatic alpha cells, it raises blood glucose by stimulating glycogenolysis and is unrelated to urine concentration. Hence antidiuretic hormone is the answer. A naming plausibility check supports it: the term diabetes insipidus signifies copious tasteless urine arising from a water-handling fault, which logically points to deficiency of the very hormone that conserves water, namely ADH.