A patient with central diabetes insipidus experiences polyuria and polydipsia due to a deficiency in antidiuretic hormone (ADH). Which part of the nephron is primarily affected by the lack of ADH, leading to impaired water reabsorption?

The correct answer to the question "A patient with central diabetes insipidus experiences polyuria and polydipsia due to a deficiency in antidiuretic hormone (ADH). Which part of the nephron is primarily affected by the lack of ADH, leading to impaired water reabsorption?" is Option D: Collecting duct.

The other options — A) Proximal convoluted tubule, B) Loop of Henle, C) Distal convoluted tubule — are incorrect for this USMLE Exam Prep question. As explained above: ADH (vasopressin) acts on the principal cells of the collecting ducts, increasing their permeability to water by inserting aquaporin-2 channels. A deficiency prevents water reabsorption here, leading…