Renal Transport Mechanisms Flashcards
Apical vs basolateral
Apical - at the lumen
Basolateral - at the interstitium
% absorbed at: PCT Glc AA urea Na K PO4 Ca Mg water
100 100 50 70 70 70 70 30 70
% absorbed at: Proximal straight tubule
PO4
15
% absorbed at: thick ascending limb Na K Ca Mg
25
20
25
60
% absorbed at: DCT Na Ca Mg H2O urea
5 8 5 var var
& absorbed at: Collecting duct
Na
H2O
urea
3
var
var
The PCT functions by reabsorbing mainly which 2 substances?
Glc
AA
PCT is how permeable to water?
Highly
Transcellular vs paracellar
Through the cell
Between cells
Symport vs antiport
Symport couples 2 solutes in the same direction.
Antiport has one go one way and another go the other.
What side is the Na/K pump on?
Basolateral
Na/K main 2 functions:
Increase extracellular Na and decrease IC Na. Create a partially negative charge inside cell.
Almost always, Na is resorbed how?
Actively and via transcellular route.
Na/H exchanger
On apical membrane of PCT
1:1 ratio
Draw the Na/H exchanger mechanism
Draw
Cl reabsorption
3
- More water than Cl is absorbed in the PCT, causing its conc. to increase along the tubule.
- Cl is filtered at the glomerulus almost freely, so its conc is the same at the glomerulus or in the first part of the PCT.
- Intraluminal conc. of Cl drives a passive diffusion from high to low conc. via the paracellular pathway.
Paracellular movement is determined by the presence of what?
Tight junctions, which retard water movement.
AQP-1
Present in PCT and descending limb
AQP-2
Present in the CD and are under control of ADH
Net water movement in the tubule is determined by which 2 factors?
Presence or absence of tight junctions.
Presence of aquaporins.
Presence of tight junctions in the PCT, descending limb and ascending limb
PCT has many tight junctions and aquaporins, making it permeable to water.
Descending limb has no tight junctions (has loose junctions instead) and AQP-1.
Ascending limb has many tight junctions and no aquaporins. Totally impermeable.
Water absorption in the PCT, LoH, and DCT
PCT is 67
LoH is 15 (only descending thin limb)
DCT is 0
What hormones regulate water permeability in the late distal tubules and collecting duct?
AVP, ANP, BNP
Glc is “almost” entirely absorbed in the PCT by which 2 transporters?
SGLT1 (90%) which is high affinity
SGLT2 (10%) which is low affinity
How do SGLTs work?
They link the movement of Na down its conc gradient with the uphill movement of Glc.
What is trying to be inhibited in the treatment of DM?
SGLT2
Inhibit reuptake of Glc.
What happens when too much Glc exists in the plasma?
After reaching the threshold (375), it is excreted in the urine causing a “sweet pee”.
Descending LoH permeabilities
Impermeable to Na
Permeable to water
Water leaves, increasing the osmolarity in the tubule.
Ascending LoH permeabilities
Impermeable to water, so NaCl s resabsorbed and the filtrate becomes less concentrated.
Why is the thick ascending limb termed the “diluting segment”?
Because it reabsorbs a high degree of solutes, causing a high degree of dilution of the filtrate.
How does the ascending limb accomplish particle reclamation?
It has a high degree of Na/K ATPase along the basolateral membrane.
Furosemide
Inhibits NaCl reabsorption by competing for Cl- binding site
Na-K-2Cl cotransporter
1 Na, 1 K and 2 Cl are reabsorbed on the apical side of the cell.
What is the set up during the Na-K-2Cl contransporter
Slide 34
Thiazide diuretics block what channel? Where?
The Na-Cl channel in the DCT.
Therefore, NaCl stays in the tubuler lumen and water follows.
How are thiazides useful in treating kidney stones?
They enhance Ca reabsorption in the DCT
CD reabsorption depends mainly on:
Which ones?
The body's needs via hormones. Aldosterone - Na ADH - water PTH - Ca Otherwise it is fairly impermeable to water.
Goals of aldosterone (4)
- Act on thick segment of nephron loop, DCT, and cortical portion of CD.
- Cause the body to retain NaCl and water
- Reduce urine vol
- Increase levels of K in the urine
