FORMATION OF DILUTE URINE & COUNTER CURRENT MECHANISM

Total body water is controlled by: 1. Fluid Intake: a. Thirst b. Salt appetite 2. Renal excretion of water and solutes

FORMATION OF DILUTE URINE ADH mechanism Renal excretion of dilute urine

ADH hormone controls hormone conc. ADH stimulated by  osmolarity ADH inhibited by  Osmolarity ADH present; 99% water Is obsorbed ADH absent ; 88% water is absorbed

Renal mechanisms for excreting a dilute urine

Counter-Current Mechanism Renal concentration of urine Counter-Current Mechanism

Independent regulation of water excretion: Counter-current mechanism

Counter-Current Mechanism Counter = opposite Current = flow Definition: A counter-current system is a system in which the inflow runs parallel to the outflow for some distance. Loop of Henle Vasa recta

Requirements for excreting concentrated urine High ADH level Hyperosmotic renal medulla Produced by COUNTERCURRENT multipliers Active transport of ions Relatively less absorption of water Urea and NaCl trapping Maintained by COUNTERCURRENT exchangers

Components 6 4 Medullary Interstitium 5a 1 to 5 Nephron Counter- Current Multipliers 3 7 Vasa Recta Counter- Current Exchangers 5b 6 1 5c 2 7

Fundamental Processes Active Transport of Na+ and co-transport of K+ and Cl- out of thick ALH Passive diffusion of Urea from inner medullary collecting duct Passive absorption of relatively large amounts of water

Permeability of different segments of nephron Nephron segment Permeability Active transport of Na+ Water Urea NaCl Proximal tubule ++ + 2+ Thin Descending Limb 4+ ± Thin Ascending Limb Thick Ascending Limb Distal convoluted tubule 3+ Cortical collecting tubule Outer Medullary collecting tubule 1+ Inner Medullary collecting tubule