1. Kidneys
kidney can alter the composition of the urine in response to the body’s daily needs, thereby maintaining the osmolality of the body fluids.
Role of ADH The principal regulator of urine composition is ADH.
In the absence of ADH kidney excretes a large volume of dilute urine& when ADH is present the kidney excretes a small volume of concentrated urine

2. Osmolality of normal urine is about 500-800mosm/L
The kidney has capacity to excrete
- dilute urine -In over hydration
30-50mosm/L with a urine flow of 20L/Day
(1/6th of the osmolar concentration of plasma]
During dehydration - concentrated urine mosm/L – (4 times the osmolar concentration of plasma] with a urine flow of 500ml/Day
with a urine flow of

3. (2) Sodium and water transport in the loop of Henle
The loop of Henle consists of three functionally distinct segments:
the thin descending segment,
the thin ascending segment,
and the thick ascending segment.

4. Reabsorb about 65-70% of filtered Sodium, Cl, Bicarbonate etc
Reabsorb essentially all glucose, aminoacids.
Secrete H+ ions 65 percent of the filtered sodium, chloride,.

5. Little or no reabsorption
High permeable to water and Highly permeable to water
Few mitochondria
Little or no reabsorption
Little or no reabsorptionpermeable to water and modeReabsorption of 25% of filtered Sodium, calcium etc
Secretion of H+ion has few mitochondria and little or no active reabsorption.
but has few mitochondria and little or no active reabsorption.
rately permeable to most solutes
Reabsorbs about 25% of the filtered loads of sodium, chloride, and potassium, as well as large amounts of calcium, bicarbonate, and magnesium.
This segment also secretes hydrogen ions into the tubule

7. Components of the concentrating & diluting system
Formation of dilute / concentrated urine is achieved by counter current system
This system consists of DLH, ALH, Medullary Interstitium, DCT, CD,
-VasaRecta - vascular element
Concentration of tubular fluid occurs mainly in JM Nephrons
of dilute/concentrated

8. Counter Current Mechanism
System in which inflow is close to, parallel to & counter to outflow for some distance
Dermal capillaries
Spermatic arteries and veins
Henle’s loop
Vasarecta

9. Countercurrent mechanism
Depends on
1) Medullary gradient
Production of Hyperosmolar interstitium –countercurrent Multiplier
Maintenance of Hyper osmolar interstitium- Counter current Exchanger
2) Levels of ADH

10. Production of hyperosmolar interstitium
Active transport of Na & other ions from thick portions of asc. limb of LOH,
Not accompanied by H2O reabsorption
Passive RA of Na from thin As.Limb
Active transport of Na from DCT &CD(cortical) (Aldosterone)
300
300
600
600
800
800
1200

11. Passive transport of urea from inner medullary collecting ducts
(ADH → permeable to urea & water)
300
300
600
600
1200
1200
Increasing osmotic gradient with increasing depth
300 mosml/ L - cortex
1200 mosml/ L - tip of medulla

12. Counter current Multiplier
consists of two limbs of loop of Henle connected by hairpin turn & the collecting duct.
The fluid flow through the three limbs is countercurrent (ie in alternating opposite directions)

13. There is a corticomedullary vertical gradient of 900mOsm/kg is established between the corticomedullaryjunction(300mOsm/kg)& the renal Papillae (1200mOsm/kg)
At any given level in the renal medulla the osmolality is almost same in all fluids except in the ALH

14. Hyperosmotic Gradient in Renal Medulla the Renal Medulla Interstitium

16. COUNTERCURRENT MULTIPLIER
Loops of Henle of juxtamedullary nephrons
The ascending limb is impermeable to H2O.
Actively co-transports Na+ and Cl- ions out of the tubular lumen into the interstitium 
Osmolarity in the ascending limb decreases
Med. Interstitial osmolarity increases

17. COUNTERCURRENT MULTIPLIER
Increased Med. Interstitial osmolarity 
Water Reabsorption from D. LOH
D.LOH – permeable to water
- Impermeable to NaCl
The fluid in the tubule is progressively concentrated as it moves down the descending limb and progressively diluted as it moves up the ascending limb.

18. ROLE OF UREA Ureaiincreases the urine osmolality
High concentration of urea in the inner medullary collecting duct causes diffusion of urea out of the collecting duct into the medullary interstitium
The interstitial urea removes water from the DLH, causes the tubular Nacl concentration to inrease above that in the interstitium favoring passive reabsorption of Nacl from thin ascending limb increases the creases

19. Figure 26.13c

20. Basics of the CC Multiplier
ALOH is only permeable to NaCl, so interstitial fluid becomes HYPEROSMOTIC compared to fluid in ALOH
DLOH- permeable to H2O, so H2O moves out into interstitium until osmolarities are now equal. Interstitial hyperosmolarity maintained during this because ALOH still pumps NaCl

21. Countercurrent multiplier – Henle’s loop
300
200
400
600
800
1000
1200
400
200
H2O
NaCl
600
400
H2O
NaCl
600
800
H2O
NaCl
800
1000
H2O
1000
NaCl
1200
H2O
NaCl

22. Countercurrent Multiplier System :

23. Vasa Recta Countercurrent Exchanger
Maintains Hyperosmolar interstitium
High resistance & “U” Shape Sluggish flow, Less blood supply
Descending limb loses water & gains solutes
Ascending limb gains water loses solutes

24. Vasa Recta is derived from efferent arterioles Maintains hyperosmolality of the medullaryinterstitium Are in juxtaposition with loop of Henle Permeable to water & solute & reach osmotic equilibrium with medullary interstitium The concentration of the Na+ & urea in the medullary interstitium are kept high by the slow blood flow in the vasaRecta

25. NaCl & Urea that have been accumulated in the interstitium are absorbed by the descending limb & returned to the interstitium by the ascending limb
The counter current Exchange traps the solutes in the medullary interstitium.
Water & solute transport occurs by diffusion&osmosis

26. Water diffuses from the descending limb the plasma protein concentration.
In the ascending limb the increase in oncotic pressure causes reabsorb fluid
In this way water reabsorbed by the nephron is removed from the interstitium & returned to the general circulation

27. Countercurrent exchanger – Vasa Recta
Blood from efferent arteriole
To vein
300
300
H2O
NaCl
NaCl
400
H2O
400
NaCl
600
NaCl
H2O
600
NaCl
800
NaCl
H2O
NaCl
800
NaCl
1000
H2O
1000
NaCl
1200
NaCl

28. VASARECTA
NaCl
H2O
NaCl
H2O
H2O
H2O
NaCl
H2O
H2O

29. Mechanism of formation of dilute urine
Bowman’s capsule- 300 mosm/L PCT – Active transport of NaCl Obligatory reabsorption of H2O 300 mosm/L (Iso osmotic) DL [LOH] - H2O by osmosis Osmolality ↑ AL [LOH] - Active transport of NaCl Osmolality↓ CT –– No ADH Dilute[Hypoosmolar] urine

30. Mechanism of formation of concentrated urine
Bowman’s capsule- 300 mosm/L PCT – Active transport of NaCl Obligatory reabsorption of H2O 300 mosm/L DL [LOH] - H2O by osmosis Osmolality ↑ AL [LOH] - Active transport of NaCl Osmolality↓ CT – Presence of ADH –Permeability to H2O ↑ Facultative reabsorption of H2O – Osmolality ↑ Concentrated [Hyperosmolar] urine

31. The Effects of ADH on the distal collecting duct and Collecting Ducts
Figure 26.15a, b

32. Formation of Water Pores: Mechanism of Vasopressin Action

33. Using sodium and other solutes.
Water reabsorption - 1
Obligatory reabsorption water reabsorption:
Using Sodium & Other solutes
Water follows the solute to the interstitium
Obligatory water reabsorption:
Water reabsorption – 2
Facultative (selective) water reabsorption
:Occurs mostly in collecting ducts
Through water channels
Regulated by ADH
Using sodium and other solutes.
Water follows solute to the interstitial fluid (transcellular and paracellular pathway).
Largely influenced by sodium reabsorption
sodium and other solutes.

34. FORMATION OF HYPER OSMOLAR URINE

36. Water Diuresis
Drinking excess water
Amount of water reabsorption in PCT is normal
↓in plasma osmolality
↓in ADH
↓in water reabsorption
Hypoosmolar urine

37. Osmotic Diuresis Unreabsorbed solutes in renal tubules 
Exert an osmotic effect
Hold water in tubules
Limits the conc gradient against which Na can be pumped out
Amount of water reabsorption in PCT is decreased
↑ in urine volume & excretion of Na & other electrolytes
Mannitol & related polysaccharides[filtered but not reabsorbed ],NaCl or urea,Glucose

38. Loop Diuretics
The key step is the active transport of NaCl out of the ascending limb. If this is abolished, eg by use of the diuretic frusemide, all concentration differences are lost and the kidney can only produce isotonic urine.

39. Applied Aspects DIABETES INSIPIDUS
ADH deficiency- Neurogenic, Nephrogenic
Neurogenic
Lesion in supraoptic & paraventricular nuclei
Lesion in Posterior pituitary
Symptoms:
polyuria &polydipsia
Tt. Clofibrate,Chlorpropamide
Nephrogenic Diabetes insipidus
Inability of kidney to respond to ADH
Gene for V2 receptor is mutated
Gene for aquaporin-2 is mutated

40. SIADH- Syndrome of Inappropriate secretion of ADH Lung Tumor-↑ADH
↑ water reabsorption
↑ ECF volume
 aldosterone secretion
Loss of salt in urine(Hyperosmolar)
Dilutional Hyponatremia
Tt. Demclocycline - decreases renal response to ADH