1.   The Body Fluids and Kidneys Lecture 16 KEEP OFF YOUR MOBILE PHONES
kidney.lecture 5b
17 February 2019
KEEP OFF YOUR
MOBILE PHONES
The Body Fluids
and Kidneys
Lecture 16  
dr.rashid mahmood

2. Water Reabsorption Passive / Osmosis
Mainly coupled to Sodium Reabsorption
Water channels made up of proteins called: AQUAPORINS
Paracellular + Transcellular

3. Water Reabsorption contd……..
Proximal Tubule
High Permeability
Solvent Drag
Distal Tubule
↓ Permeability
i. Tighter junctions
ii. ↓ Surface Area
Ascending Loop of Henle
Almost Zero Permeability
More Distal Parts
ADH

4. Reabsorption of Urea & Chloride

5. Proximal Tubule

6. Reabsorption in First half of Proximal tubule
Active Transport:
1. Primary Active Transport
Sodium( Sodium-Potassium ATPase)
2. Secondary Active Transport (Co-Transport)
Glucose, Amino Acids, Organic Acids
Passive Transport:
Water,
Urea? Chloride ?

7. Reabsorption in Second half of Proximal tubule
Active Transport:
1. Primary Active Transport
Sodium( Sodium-Potassium ATPase)
2. Secondary Active Transport (Co-Transport)
Chloride
Passive Transport:
Water,
Glucose, Amino Acids ?
Urea reabsorption and secretion

8. Secretion in Proximal tubule Counter TransportH+
Organic Acids + Bases
e.g.
Bile Salts
Oxalate
Urate
Catecholamines
Drugs
Toxins
PAH (Para-Amino- Hippuric Acid)

10. Reabsorption of various solutes in proximal tubule

11. Reabsorption in Loop of Henle
20%
Urea reabsorbed
Back in
Thin Ascending Limb

12. Reabsorption in Loop of Henle Thin descending segment
Structure
Thin epithelial membrane
No brush border
Few mitochondria
Function
Highly Permeable to water
Almost all water absorbed in Loop of Henle is absorbed here →↑osmolarity
Moderately permeable to most solutes, including Sodium and Urea
No active transport

13. Reabsorption in Loop of Henle Thin ascending segment
Structure
(Same as descending limb)
Thin epithelial membrane
No brush border
Few mitochondria
Function
Impermeable to water
Permeable to NaCl
No active transport
Urea is reabsorbed back
Juxta -medullary nephrons

14. Reabsorption in Loop of Henle Thick ascending segment
Structure
Thick epithelial cells
Function
Na+-K+ ATPase in basolateral membrane
i) Active reabsorption of Na+, K+, Cl- (about 20-25% of filtered load) (Secondary active transport)
(1-Sodium, 2-chloride, 1-Potassium co-transporter)
ii) Reabsorption of Ca++, HCO3--, Mg++
2. Paracellular reabsorption of Ca++, K+, Mg++, Na+
3. Na+ -H+ Counter-transport
4. Impermeable to water →↓osmolarity (dilute tubular fluid)
Loop diuretics

15. Reabsorption in Loop of Henle
20% Water Reabsorbed in Loop of Henle
25% Sodium Reabsorbed in Loop of Henle
some Passive Reabsorption of Urea
No Water Reabsorption in Ascending Limb
No Active Transport in Thin Limb

16. Transport in Thick Ascending Loop of Henle

17. NaCl transport in thick ascending limb of loop of Henle

18. Reabsorption in Distal Convoluted Tubule
Juxta Glomerular Apparatus
Early Distal Tubule
Almost same as Thick Ascending Loop of Henle
(5% sodium reabsorption in early DCT)
Diluting Segment

19. Reabsorption in Distal Convoluted Tubule
water
Aldosterone
Aldosterone
H+ ATPase

20. Mechanism of Na+ Reabsorption in Distal Convoluted Tubule
Early
Late
K+ sparing diuretics

21. Reabsorption in Second Half of Distal Convoluted Tubule
Water Reabsorbed from both cells in the presence of ADH (Anti-Diuretic Hormone)
Impermeable to urea
Na+ reabsorption and K+ secretion under influence of Aldosterone
Active secretion of H+

22. Cortical Collecting Tubule
Same as second Half of Distal Collecting Tubule

23. Medullary Collecting Duct

24. Tubular processing in Medullary Collecting Duct
Structure
Cuboid
Smooth surface
Few mitochondria
Function
Reabsorption of 10% of water and sodium
Final site of processing of urine
ADH
Permeable to urea
H+ secretion

25. Summary
Contd…

26. Summary (ADH present)