1. URINE CONCENTRATION AND REGULATION OF ECF OSMOLARITY

2. Dilute and concentrated urine
1-Dilute urine : Nephron function continuous reabsorption. Solutes while failing to reabsorbe water in distal tubule and coll. duct by reducing ADH secretion  urine excreted with 50 mOsm/L or with high ADH urine osmolarity can reach to mosm/L
If large excess of water in the body, kidneys excrete up to 20 L/day

5. ADH (VASOPRESSIN) Increase osmolarity (Reduce ECF) increase ADH which increase permeability of distal tubules and collecting ducts to water which increase H2O absorption and decrease urine volume and vice versa

6. Proximal tubule: Reabsorption for water and solutes are equal proportion (Remain isosmotic)
Descending: H2O reabsorbed by osmosis & fluids reaches equilibrium with surrounding interstitium (Hypertonic) .
Ascending: especially thick, water impermeable, solutes heavily reabsorbed osmolarity about 100 mOsm/L(Hypotonic). No effect of ADH
Early distal : same as above50 mOsm/L.
Late dist & coll duct: ADH effect

7. * From proximal tubule Filtrate has concentration
of 100 mosm/liter as it
enters distal and
collecting tubules
Distal tubule
Cortex
Loop of
Henle
Medulla
In the
face
of a
water
excess
Collecting
tubule
FIGURE 13-20: Excretion of urine of varying concentration depending on the body’s needs.
Concentration of
urine may be as low
as 100 mosm/liter
as it leaves
collecting tubule
= passive diffusion of H2O
= portions of tubule
impermeable to H2O
= permeability to H2O
increased by vasopressin *
= active transport of NaCl
Fig b, p. 433

8. Forming concentrated urine
2-Concentrated urine : Maximum urine
concentration mOsmole/L.
Australian hopping mouse mOsm/L.
For concentrated urine need High ADH level &
Hyperosmotic renal medulla
Obligatory urine volume 70 Kgm human excrete 600 mOsm/day minimal volume of urine = 600 mosm/day = 0.5 L/d
1200 mOsm/L

10. Urine Specific Gravity = Weight of solutes in a given volume, determined by size and numbers of solute molecules. Urine osmolarity = Determined only by the number of solute molecules in given volume.

12. Countercurrent mechanism . C.C. Multipleir
-Factors contribute in building hyperosmolar medulla:
1. Active transport of Na, and Co-transport of Cl- and K+, and other ions in thick L.H
2. Active transport of ions from collecting ducts into medulla
3. Passive diffusion of urea from inner modularly coll. duct
4. Water diffusion far less than solutes

13. -. Repetitive reabsorption of NaCl by thick L
- Repetitive reabsorption of NaCl by thick L.H and inflow new NaCl from proximal tubule [counter current multipleir]
- Urea passively reabsorbed from tubule (inner medullary collecting ducts), then diffuses into thin L.H [urea recirculated and creates 500 mOsm/L] .

15. All values in milliosmols (mosm)/liter.
Medulla
Cortex
FIGURE 13-17: Vertical osmotic gradient in the renal medulla. Schematic representation of the kidney rotated 90° from its normal position in an upright person for better visualization of the vertical osmotic gradient in the renal medulla. The osmolarity of the interstitial fluid throughout the renal cortex is isotonic at 300 mosm/liter, but the osmolarity of the interstitial fluid in the renal medulla increases progressively from 300 mosm/liter at the boundary with the cortex to a maximum of 1200 mosm/liter at the junction with the renal pelvis.
All values in milliosmols (mosm)/liter.
Fig , p. 427

18. * Filtrate has concentration From of 100 mosm/liter as it proximal
enters distal and
collecting tubules
From
proximal
tubule
Distal tubule
Cortex
Loop of
Henle
Medulla
In the
face
of a
water
deficit
Collecting
tubule
FIGURE 13-20: Excretion of urine of varying concentration depending on the body’s needs.
Concentration of
urine may be up
to 1,200 mosm/liter
as it leaves
collecting tubule
= passive diffusion of H2O
= portions of tubule
impermeable to H2O
= permeability to H2O
increased by vasopressin *
= active transport of NaCl
Fig a, p. 433

19. ROLE OF DIST TUB & COLL DUCT IN EXCRETE CONCENTRATED URINE 1-In cortical collect tub (ADH) large amount of water absorbed more than in the medulla to preserve the high medullary interstitial fluid osmolarity 2-In medullary collect duct , still more water absorbed but smaller than cortical & absorbed water carried by vasa recta. With high ADH the fluid in the collecting duct has same osmolarity as interstitial fluid of the renal medulla

21. Urea contribute to hyperosmotic renal medullary interstitium :
1-Contribute about 40-50%
2-Urea passively absorbed from the tubule
3-Little urea absorbed in ascending limb, distal & cortical collecting tubules(not permeat to urea) .
4-In the presence of ADH in cortical coll ,water absorbed and then in medullary collecting duct cause ^ concentration of urea

22. 5-Diffuse of urea to medullary interstitium facilitate by specific urea transporter(UT-AI)
& (UT-A3) activated by ADH
6-Some urea secreted in thin loop from medullary interstitium facilitated by (UT-A2) .
This Recirculation of urea is additional mechanism for forming hyperosmotic renal medulla

25. VASA RECTA:
1-Less than 5% of renal blood flow
2-Countercurrent exchanger ,reduce wash out of solutes from medullary interstitium
3-During descending blood becomes concentrated by solutes enter and H2O loss
4-In Ascending part vice versa.
5-It prevent medullary hyperosmolarity from dissipated.

28. Role of early distal & coll.: - if there is no ADH
this part still impermeable to water.
- if there is ADH
this part is highly permeable to water. Water will leave from cortical and from juxtamedulary nephrones , but majority in cortex, to preserve the high medullary interstitial fluid osmolarity. -

29. B] C.C. exchanger: - Factors keeping hyperosmolarity :
a. Medullary blood flow is low 1to2% of total renal blood flow.
b. Vasa recta structure: descending and ascending segment.
U-shape minimizes loss of solute from interstitial but does not prevent the bulk flow of fluid & solutes into blood through(starling capp. circ.)

30. Regulation of ECF osmolarity and Na concentration
1-Osmoreceptor (hypothalamus)- ADH feedback system: H2O deficit-^ osmolarity- ^ADH- ^H2O permeability in DT and collecting duct- ^H2O reabsorption-decrease H2O excretion.

32. ADH Synthesis in the Hypothalamus and
Release from Posterior Pituitary
CV Reflex stimulation of ADH Secretion:
Decrease Blood Volume, Decrease BP
Other stimuli for ADH secretion :Nausea, nicotine, morphine. But alcohol inhibit ADH secretion and cause diuretic.

34. Regulation of ECFosmolarity and Na concentration
2-Osmolarity and Thirst Conscious desire for water Thirst center ,Third ventricle area that promot ADH release stimulate thirst center

35. Thirst Increase with A-Increase osmolarity (Salt) B-Decrease Blood vol
C-Decrease BP
D-Increase angiotensin II
E-Dryness of mouth

36. ADH and thirst mechanism work in parallel to regulate ECF osmolarity and Na concentration more effective .
Angiotensin II and aldosterone have little effect on Na concentration but not the Na quantity and volume (increase absorption of both water and Na).

37. SALT APPETITE: Decrease extracellular fluid Na concentration, Decrease Blood Volume and BP
Neural mechanism for salt appetite is analog to that of thirst mechanism.