2. A system in which the inflow runs parallel to,
counter to, and in close proximity to the outflow
for some distance.
Conditions to be fulfilled,
2 tubes in parallel
movement in opposite direction
in close proximity & selectively permeable
3. Maintenance of air temperature in a
furnace
Countercurrent mechanism helps Penguin
to stand on ice for long time.
4. Skin (heat conservation)
Scrotum (exchange of heat & testosterone)
Kidney – ability to concentrate urine,
a critical adaptation of life on
land through evolution
5. Depends upon maintenance of a gradient
of increasing osmolality along the
medullary pyramids.
Counter current multiplication system-
Loop of Henle
Counter current exchange system –
Vasa recta
6. • long loop of Henle establishes a vertical osmotic
gradient (Countercurrent multiplier)
• their vasa recta preserve this gradient while
providing blood to renal medulla (
Countercurrent exchanger)
• collecting ducts of all nephrons use the gradient in
conjunction with the hormone vassopressin, to
produce urine of varying concentration (osmotic
equilibrating device)
Collectively this entire functional organization is
known as medullary countercurrent system
7.
8. A large, vertical osmotic
gradient is established in
the interstitial fluid of the
medulla
(from 100 to 1200
mosm/liter)
This osmotic gradient
exists between
the tubular lumen and
the surrounding
interstitial fluid.
9. Process in which small osmotic gradient
established at any level of LOH is multiplied in to
larger gradient.
Single effect
Active transport of Na & Cl out of thick ascending
limb
High permeability of thin descending limb to
water
Solute deposition in medulla & removal of water
from descending limb
20. Inflow of fresh
filtrate and
equilibration with
the medullary
interstitum
300
300
350
350
500
500
150
150
300
300
500
500
300
300
350
350
500
500
21. Tranporters work
again to reach a
gradient of 200
mosm
Process is repeated
again and again
Thus a single effect
gets multiplied
300
300
350
350
500
500
125
125
225
225
400
400
325
325
425
425
600
600
23. Descending limb is highly permeable to water
but impermeable to solutes
Thin ascending limb is passively permeable to
solutes
In thick ascending limb, Na & Cl are actively
transported (Na/K/2Cl)
24.
25. Solute gradient created by LOH in medulla is
maintained by vasa recta
Decrease solute dissipation
In descending limb, solutes diffuse into vessels
In ascending limb, solutes diffuse out of vessel
Thus solutes keep circulating
Water diffuses out of descending limb and into
ascending limb
While solutes recirculate in medulla, water is
removed from it
28. Acts as osmotic equilibrating device, by its
permeability to water & urea
use the gradient, created by LOH &
maintained by vasa recta, in conjunction
with the hormone vasopressin, to produce
urine of varying concentration
29.
30. Vasopressin-controlled, variable water reabsorption
occurs in the final tubular segments.
65% of water reabsorption is obligatory in the proximal
tubule. In the distal tubule and collecting duct it is
variable, based on the secretion of ADH.
The secretion of vasopressin increases the permeability
of the tubule cells to water. An osmotic gradient exists
outside the tubules for the transport of water by osmosis.
Vasopressin works on tubule cells through a cyclic AMP
mechanism.
During a water deficit, the secretion of vasopressin
increases. This increases water reabsorption.
During an excess of water, the secretion of vasopressin
decreases. Less water is reabsorbed. More is
eliminated.
31.
32. Every time tubular fluid passes through LOH,
Water comes out of descending limb into interstitium,
which is removed by ascending limb of vasa recta
Solutes come out of ascending limb into interstitium
Thus, high osmolality is maintained in medulla
This causes movement of water out of the
Collecting Duct & makes the urine concentrated
33. DIURETICS
drugs that increase the rate of urine flow
their clinical applications aim to reduce ECF
volume by decreasing total body NaCl content
34. TYPE Site of
Action
Examples
1. Inhibitors of Carbonic
Anhydrase
PCT Acetazolamide,
Methazolamide
2. Osmotic diuretics LOH Glycerine,
Isosorbide,
Mannitol,Urea
3. Inhibitors of Na-K-2Cl
symport
(Loop diuretics /High
ceiling diuretics
Thick AL of
LOH
Furosemide,
Bumetamide,
Torsemide
35. TYPE Site of
Action
Examples
4. Inhibitors of Na-Cl
symport
(Thiazide-like
diuretics)
DCT Chlorothiazide,
Hydrochlorothiaz
ide,
5. Inibitors of renal
epithelial Na channels
(K-sparing diuretics)
Late DCT
& CD
Amiloride,
Triamterene
6. Antagonists of
mineralocorticoid
receptors
(Aldosterone
antagonists/
K-sparing diuretics)
Late DCT
& CD
Spironolactone
36. Diuretic Braking
Compensatory Mechanisms:
Activation of sympathetic nervous system
Activation of R-A-A axis
Decreased arterial BP
Hypertrophy of renal epithelial cells
Increased expression of renal epithelial
transporters