Counter current mechanism

1. Counter Current Mechanism
Dr.Sara Sadiq

2. Countercurrent Mechanism
• Interaction between the flow of filtrate through the loop of Henle
(countercurrent multiplier) and the flow of blood through the vasa
recta blood vessels (countercurrent exchanger)
• The solute concentration in the loop of Henle ranges from 300 mOsm
to 1200 mOsm

4. Water Permeability
--In the proximal tubule, the water permeability is always high.
--In the ascending loop of Henle, water permeability is always low, so
that almost no water is reabsorbed.
--Water permeability in the distal tubules, collecting
tubules, and collecting ducts—can be high or low, depending on the
presence or absence of ADH.

5. PCT

9. Transport Maximum
Transport maximum For most substances that are
actively reabsorbed or secreted, there is a limit to the
rate at which the solute can be transported.
when the tubular load exceeds the capacity of the
carrier proteins involved in the transport process this
substance will appears in urine.

11. Ascending Limb of the Loop of Henle

12. 14-28b

13. 14-28c

14. 14-28d

15. 14-28e

16. 14-28f

17. 14-28g

18. Early Distal Tubule

19. 14-29
Late DCT & CD (Principal Cells)

20. Late DCT & CD (Principal Cells)

21. Late DCT & CD (Intercalated Cells)

23. Urea Reabsorption
• Contributes to total
osmolality of interstitial
fluid.
• Ascending limb LH and
terminal CD are permeable
to urea.
• Terminal CD has urea
transporters.
• Recycle urea.

24. Formation of Dilute and Concentrated Urine
Figure 25.15a, b

25. Vasa Recta
• Countercurrent exchange.
• Recycles NaCl in medulla.
• Transports H20 from
interstitial fluid.
• Descending limb:
• Urea transporters.
• Aquaporin proteins (H20
channels).
• Ascending limb:
• Fenestrated capillaries.

26. Osmolality of Different Regions of the Kidney
Insert fig. 17.19

29. Thank You