1. FORMATION OF DILUTE URINE & COUNTER CURRENT MECHANISM

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

3. FORMATION OF DILUTE URINE
ADH mechanism
Renal excretion of dilute urine

4. 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

5. Renal mechanisms for excreting a dilute urine

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

8. Independent regulation of water excretion: Counter-current mechanism

9. 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

10. 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

11. 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

15. 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

16. 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