<prompt> In the presence of vasopressin the greatest fraction of filtered water is re-absorbed which pa of the nephron:Proximal tubuleDistal tubuleLoop of HenleLoop of Henle  <response>: 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 tubule60-70Q60-700Loop of Henle1515Distal tubule55Collecting duct210QThus the greatest fraction of filtered water 60-70 is reabsorbed in proximal tubule irrespective of presence or absence of vasopressinQ. 