Renal 3 Flashcards
What percentage of water, Na+, and Cl- are reabsorbed in the kidneys? What about glucose?
over 99% of water, Na+, and Cl- are reabsorbed
100% of glucose is reabsorbed (if blood levels aren’t super high)
What is the difference between paracellular transport and transcellular transport?
Paracellular is when solutes move between the tight junctions at cell borders.
Transcellular is when stuff goes into the cell, then is transported out on the other side.
What is solvent drag?
When solutes follow water as it is transported across cell membranes.
____% of Na+, Cl- and water are reaborbed in the proximal tubule. This reabsorption is _________ since water follows.
67%. Water follows - isoosmotic
How does the basolateral Na+/K+ ATPase affect intracellular solute concentration?
It keeps Na+ concentration at around 10mM, vital for moving around other solutes.
What transporter is used in PCT cells (first half of the PCT) to resorb sodium? What other processes are necessary to keep this going?
Sodium enters via the Na+/H+ antiporter.
H+ is needed to keep it going, which is recycled in the following way:
- Carbonic anhydrase on the apical cell membrane catalyzes H2CO3 –> H2O + CO2.
- CO2 diffuses into the cell.
- CO2 combines with H2O in the cell and carbonic anhydrase catalyzes –> H2CO3 –> H+ + HCO3-.
- The H+ from this is used for the Na+/H+ antiporter, and the HCO3- goes out into the interstitium with either the Cl-/HCO3- exchanger or Na+/HCO3- cotransporter (voltage driven).
What specifically do diuretics act on in PCT cells?
They inhibit carbonic anhydrase –> stops sodium reabsorption, water doesn’t follow.
How is glucose reabsorbed in 1st half PCT cells? How does it exit on the basolateral side?
glucose gets into the cell with a Na+/glucose co-transporter and exits on the basolateral side through a passive transporter.
What is cystinuria?
Loss of the Na+-coupled amino acid transporter in the 1st half of the PCT (characterized by kidney stones).
What is different about how Na+ is reabsorbed in the 2nd half of PCT cells?
The transporter is still a Na+/H+ antiporter; the difference is where the H+ comes from: H+ couples with anions like formate in the tubule lumen, which diffuse into the cell. These dissociate into the cell and the H+ is used for the Na+ antiporter. The anion is transported back to the tubule lumen with the Cl-/anion exchanger.
What are the two mechanisms of Cl- reabsorption in 2nd half PCT cells? How does Cl- exit at the basolateral side?
Reabsorption via paracellular and the Cl-/anion exchanger.
It exits the basolateral side with the K+/Cl- cotransporter
State what generally happens in each segment of a nephron.
PCT reabsorbs most of the Na+, Cl-, and H2O (isoosmotic).
Loop of Henle reabsorbs a ~25% of Na+, Cl-, and H2O. The descending loop is permeable to water, the ascending loop is not and reabsorbs NaCl.
The DCT reabsobs the rest of Na+ and Cl- and also responds to ADH for additional water reabsorption.
What is the osmolarity of the interstitial fluid of the inner medulla? Why is this useful?
Very high (1200mOsm). This makes water come out of the tubule.
How are solutes (Na+, Cl-, K+) reabsorbed in the thick ascending limb of Henle?
Na+, K+ and Cl- are taken up together via the Na+/K+/2Cl- cotransporter (driven by Na+ gradient). Paracellular cation transport also occurs from the potential set up by K+ release from cells into the tubule lumen.
Na+ is also reabsorbed from lumen by the Na+/H+ antiporter.
What does furosemide do?
Inhibits the Na+/K+/2Cl- cotransporter in the thick ascending limb of Henle
