8. Renal Transport Mechanisms – NaCl and Water Absorption along the Nephron Flashcards
What percentage of water and sodium is reabsorbed in the proximal convoluted tubule?
65 to 70%
What is the primary player in resorption?
Na/K ATPase
What is the advantage of taking a paracellular route?
The paracellular route does not require energy.
Where is the Na/K ATPase pump physically located?
In the basolateral membrane
What form of cellular transport is utilized in the reclamation of bicarbonate?
Trans-cellular
What 2 actions are completed by carbonic anhydrase in the reclamation of bicarbonate?
- The initial conversion of bicarbonate and hydrogen into carbonic acid
- The conversion of carbonic acid back into bicarbonate and hydrogen within the cell
What form of cellular transport is utilized in chloride reabsorption?
How does this occur?
Paracellular movement
More water than chloride is the absorbed in the 1st half of the proximal tubule, so the concentration of chloride increases. This creates a gradient for passive movement of chloride paracellularly.
Do we see more water transport in the thin descending limb of the loop of Henle, or the thick ascending limb of the loop of Henle?
Water flows freely out of the thin descending limb of the loop of Henle through both aquaporin proteins and loose junctions.
The thick ascending limb is impermeable to water, it has both tight junctions and a lack of aquaporin.
Where do we find aquaporin I proteins in the nephron?
In the proximal tubule, as well as in the thin descending limb of the loop of Henle.
Where do we find aquaporin II proteins?
In the collecting duct and late distal tubule.
What type of water movement is allowed in the collecting duct and late distal tubule?
Transcellular water movement only:
there are tight junctions, but they are also aquaporin II channels.
What is the main glucose transporter (the glucose transporter that is responsible for the majority of glucose)?
SGLT2
What transporter did we talk about as a common target for diabetic drugs?
SGLT2
Approximately how much water is absorbed by the descending loop of Henle?
15% of water filtered is through the descending loop of Henle
How is the descending loop of Henle able to concentrate solutes in the tubular fluid?
By re-absorbing water, but being impermeable to sodium chloride.
How does the ascending loop of Henle modify the concentration of the tubular fluid?
It decreases the concentration by being impermeable to water, but allowing the reabsorption of solutes.
How much sodium is absorbed by the ascending loop of Henle?
Approximately 25% of the filtered sodium
Where do we find the Na-K-2Cl cotransporter?
On the thick ascending loop of Henle
Where do we see the Na/Cl co-transporter?
Why do we care about it?
In the distal tubule
Because it is inhibited by thiazide diuretics
How does furosemide function?
It inhibits sodium chloride reabsorption by competing for the chloride binding site on the Na-K-2Cl transporter.
What type of cell does aldosterone target, and what is it doing?
It targets the principal cells of the collecting duct, in order to increase luminal Na-K transporters. This increases sodium reabsorption and decreases potassium reabsorption.
How do thiazide diuretics function?
They inhibit reabsorption of sodium and chloride in the distal convoluted tubule by inhibiting the sodium chloride symporter.
They also reduce urinary excretion of calcium (increase reabsorption of calcium).
How does spironolactone function?
It is essentially the opposite of aldosterone, and inhibits sodium potassium exchange in the other direction.
Potassium is spared and sodium is lost (along with water)
