In the presence of vasopressin, the greatest fraction of filtered water is absorbed in:
Water absorption in different segment of nephron Segment % absorption Through Proximal tubule 60-70% AQP 1 Descending loop of Henle 15% AQP 1 Ascending LOH (Diluting segment) Impermeable to water Distal Tubule Relatively impermeable to water (~5% in ADH presence in late DT) Collecting Duct 1. Coical 2. Medullary In absence of ADH, CD is relatively impermeable to water (~2%) 10% (in presence of ADH) ~5% (in presence of ADH) AQP 2 on ocal and AQP 3,4 on basolatreral membrane ADH dependent absorption is 20% only, even in presence of ADH maximum absorption is occurring from PCT Obligatory water absorption Facultative water absorption Approx, 80% (65% in PCT, 15% in loop of henle) Approx, 20% (from collecting duct and late distal tubule) Water is obligated to follow solutes, irrespective of blood osmolality Depends on blood osmolality Independent of ADH Depends on ADH
Proximal tubule
Loop of Henle
Distal tubule
Collecting duct
Excretory System