This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Fluid and electrolytes, Subject name: Medicine
[{'content': 'All regulation of renal potassium excretion & total body potassium balance occurs in \nSelect and explain. \nA. Proximal convoluted tubule, B. Ascending loop of Henle, C. Descending loop of Henle, D. Collecting duct', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Changes in whole-body K+ content are primarily mediated by the kidney, which reabsorbs filtered K+ in hypokalemic, K+-deficient states and secretes K+ in hyperkalemic, K+-replete states. Although K+ is transpoed along the entire nephron, it is the principal cells of the connecting segment (CNT) and coical CD that play a dominant role in renal K+ secretion, whereas alpha-intercalated cells of the outer medullary CD function in renal tubular reabsorption of filtered K+ in K+-deficient states. Ref: Harrison 19e pg: 304', 'role': 'assistant'}]