Tubular Function Flashcards
Why is tubular reabsorption necessary
With average ( 125 ) GFR the entire plasma volume is filtered every 30-40 minuets so all this fluid can’t be lost and so tubular absorption allows only 1-2 L of fluid to be lost through urine
Where does tubular reabsorption occur
Across epithelial cell all around the nephron especially in the PCT
How do molecules move fro filtrate into the blood or vice versa
1- Move through gaps in cells ( paracellular ) 2- Move through cells (transcellular ) 3- reabsorption ( filtrate to blood ) 4- secretion ( blood to filtrate ) 5- excretion ( via urine )
How is Glucose reabsorbed ( where , how and how much )
PCT reabsorbs 100% of filtered glucose.
Glucose is reabsorbed using GLUT2 transporter and SGLT1&2
What limits the maximal transport of glucose
Too much glucose and not high enough rate of glucose transported
What is transport maximum
the maximum rate of a substance’s reabsorption
What can cause glucosuria
Reabsorption dysfunction or SGLT2 inhibitor drugs slowing down transport rate in PCT
How are Amino acids reabsorbed ( where, how , and how much )
Over 95% Reabsorbed in PCT.
Transport maximum system that limits amino acid reabsorption depending on speed of pump.
What can cause Aminoaciduria
disorders of amino acid metabolism which doesn’t allow them to be reabsorbed or transport protein defect
How is Sodium reabsorbed ( where, how and how much )
1- 70% reabsorbed in PCT.
Transported via glucose , amino acids and sodium-hydrogen pump / sodium-potassium ATPase.
2- 20% reabsorbed in ascending Loop of Henle via co transporters K and Cl
3- 5 % reabsorbed in DCT
4- 3 % reabsorbing in collecting ducts
5- 2 % excreted
What limits the reabsorption of sodium ( Hint : 2 limitations )
It’s gradient limited in the PCT and Acc Loop.
Pump expression limited by aldosterone in DCT and Ducts
When is sodium wasting used and how does it work
In hypertension and Heart failure. Block aldosterone and diuretics .
What influences water reabsorption
the movement of sodium
How is water reabsorbed ( where and how much )
1- 65% at PCT
2- 15% at descending loop of henle
3- ADH dependent on DCT and ducts
Explain how water is reabsorbed at the loop of Henle ( Hint : 6 steps )
Via the counter-current multiplier mechanism.
1- Limbs of LH are arranged to flow( down ) in opposition to flow of vasa recta ( up )
2- sodium passively moves into vasa recta from ASC loop making the blood concentrated
3- this promotes H2O reaborsption in the dsc loop since it shares vasa recta with acc loop
4- filtrate moves down dsc loop to asc as the filtrate is becoming more concentrated
5- makes more sodium move out from asc loop into blood
6- filtrate becomes dilute in Asc as sodium moves out
