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
[{'content': 'In the presence of vasopressin the greatest fraction of filtered water is re-absorbed which pa of the nephron: \nSelect and explain. \nA. Proximal tubule, B. Distal tubule, C. Loop of Henle, D. Loop of Henle', 'role': 'user'}, {'content': 'Answer: A \nExplanation: A i.e. Proximal tubuleVasopressing acts on the collecting ducts and enhances their permeability to water.When vasopressing is absent- The collecting duct epithelium is relatively impermeable to water and only 2% of water is reabsorbed.- However by the time water reaches collecting duct, a maximum of 60-70% has already been re- absorbed in the proximal tubules. % of water reabsorbed inabsence of vasopressin% of water reabsorbed inpresence of vasopressinProximal tubule60-70%Q60-70%0Loop of Henle15%15%Distal tubule5%5%Collecting duct2%10%QThus the greatest fraction of filtered water (60-70%) is reabsorbed in proximal tubule irrespective of presence or absence of vasopressinQ.', 'role': 'assistant'}]