1. TUBULAR REABSORPTION Part II
DR .IMRANA EHSAN

3. Solute and water reabsorption inLoop of Henley

4. Reabsorption in the Loop of Henle
Tubular fluid
PCT reabsorbed 65% of the filtered water so chemical composition of tubular fluid in the loop of Henle is quite different from plasma since many nutrients were reabsorbed as well, osmolarity of tubular fluid is close to that of blood
Sets the stage for independent regulation of both volume & osmolarity of body fluids.
THIN DESCENDING LIMB: Highly permeable to water and moderately permeable to solutes.
20% of fluid reabsorbed

5. Symporters in the Loop of Henle
ASCENDING LIMB :
THIN ASCENDING LIMB: impermeable to water.
Thick ascending limb: has Na+ K- Cl- symporters on liminal side that reabsorb these ions
K+ leaks through K+ channels back into the tubular fluid leaving the interstitial fluid and blood with a negative charge
Na/Kpump on basolateral membrane
Ca, Mg, Na ,K passively move to the vasa recta BY PARACELLULAR ROUTE.

6. DESCENDING LOOP OF HENLE: No active transport of salt out of the descending loop of Henle.
ASCENDING LOOP OF HENLE: Chlorine ions actively transported out of loop into the interstitial space. Oppositely charged sodium ions follow. However, water does not move out of the ascending loop.
A concentration gradient IN THE INTERSTITIAL SPACE has been set up by the chlorine ( plus sodium) transport.

7. Early distal convulated tubule:
Reabsorption on the early distal convoluted tubule
Na+-Cl- symporters reabsorb Na+ and Cl-, Ca,Mg.
Na/K Pump at basolateral membrane
Na Cl cotransport on luminal surface
Major site where parathyroid hormone stimulates reabsorption of Ca+ depending on body’s needs
Reabsorption and secretion in the late distal convoluted tubule and collecting duct
90-95% of filtered solutes and fluid have been returned by now
Principal cells reabsorb Na+ and secrete K+
Intercalated cells reabsorb K+ and HCO3- and secrete H+
Amount of water reabsorption and solute reabsorption and secretion depends on body’s needs

8. Early distal covulated tubule

9. DISTAL TUBULE AND CORTICAL COLLECTING DUCTS

10. Medullary collecting ducts

11. Hormonal regulation of tubular reabsorption and secretion
Glomerulotubular balance
Increased tubular load increases reabsorption rates
Angiotensin II - when blood volume and blood pressure decrease
Decreases GFR, enhances reabsorption of Na+, Cl- and water in PCT
Aldosterone - when blood volume and blood pressure decrease
Stimulates principal cells in collecting duct to reabsorb more Na+ and Cl- and secrete more K+
Parathyroid hormone
Stimulates cells in DCT to reabsorb more Ca2+
2nd line of defence
Prevents overloading of distal tubular segments

12. Fluid flow in pertubular compartment