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: Physiology
Over half of the potassium that appears in the urine of a patient, who has ingested some potassium salts, is derived From? 
Select and explain. 
A. Glomerular filtrate, B. Secretion by the distal tubule, C. Reabsorption in the proximal tubule, D. Secretion by the loop of Henle
B: Secretion by the distal tubule
Answer: B: Secretion by the distal tubule 
Explanation: Secretion by the distal tubule.With a normal potassium intake filtered K+ (which is not reabsorbed) accounts for two third and secreted K+ counts for one-third of the excreted urinary K+.However, on high potassium diet, the K+ secretion increases and K+ secretion account for about 60-65% excreted K+.K+ secretion occurs in distal tubules and collecting duct.