Flashcards in Week 7, lecture 1 Deck (61)
About what total % is the filtrate reabsorbed at the PT?
What is iso-osmotic reabsorption? What is it in terms of a ratio?
What is reabsorbed iso-osmotically at the PT?
- Water reabsorption occurs in = proportion w/reabsorbed solutes
- tubular conc : plasma conc osmolality ratio of 1.0
What is the only thing reabsorbed at the PT with a [TF]/[P]x100 ratio greater than 100?
What % of it is reabsorbed at the PT?
What % of Na+ is reabsorbed at the PT?
67% (H2O follows)
What % of Pi is reabsorbed at the PT?
What % of HCO3- is reabsorbed at the PT?
What other 3 things are reabsorbed at a rate of ~90% at the PT?
Glucose, lactate, and amino acids
What is the tubular lumen potential (RMP) at the PT?
Why is it what it is?
Because there are leaky tight junctions
What does a value > 100 of [TF]/[P]x100 indicate?
> 100 = relatively less of the solute vs. H2O reabsorbed
In the first 1/2 of the PT, what is Na+ reabsorbed w/ (secondary active symport)?
HCO3-, PO43-, glucose, amino acids, lactate
Name all of the transporters found on the apical side of the first 1/2 of the PT.
- Na+ taken up passively
- Na+/H+ antiporter (secondary)
- Na+/glucose symporter (secondary; along w/Na/X xporters?)
What creates the gradient for apical Na+ coupled xport in the first 1/2 of the PT?
Which side of the cell is it on?
- Na-K pump
- Basolateral side
Once symported into the apical side of the cell w/Na+, how do HCO3-, PO43-, glucose, amino acids, and lactate get across the basolateral side of the first 1/2 of the PT?
Facilitated diffusion, mostly
What causes the RMP in the first 1/2 of the PT?
How did it get into the cell?
How does it get out of the cell?
- Got in thru NKP
- Gets out thru passive diffusion
What are the ratios of ion movement with the Na/HCO3- symporter in the first 1/2 of the PT?
How else are HCO3- ions moved out of the basolateral membrane?
1x Na+ - 3x HCo3- symporter
Cl- HCO3- antiporter
W/ what is Na+ reabsorbed w/in the 2nd half of the PT, primarily?
Thru what general pw's is Na+ reabsorbed in the 2nd half of the PT?
What % reabsorption occurs thru each?
What other thing is reabsorbed here via these 2 methods?
Transcellularly (67%) and paracellularly (33%)
In the 2nd half of the PT, what 2 ways do Na+ and Cl- cross the apical membrane to be reabsorbed?
What can form, and how does the process continue?
Parallel Na+-H+ and Cl--anion antiporters
- H+Anion complexes can form in tubular fluid that can recycle across the apical membrane to bring in more Na+ and Cl- (anions are secreted into urine)
In the previous example of Na+ and Cl- antiport across the apical membrane w/ an anion, what forms can the anion take?
OH- (hydroxide), HCO2- (formate), oxalate, HCO3-, sulfate
What enzyme is found in the FIRST half of the PT that involves one of the things we've talked about?
What does it do?
Carbonic anhydrase (CA), creating bicarb from CO2 and H2O, this increasing acidity via H+ production
What is the transepithelial potential at the 2nd 1/2 of the PT? What is the potential in the blood?
What generates this transepithelial potential??
+4mV (lumen is -4mV; blood is 0)
- Generated by the diffusion of Cl- (lumen to blood) across the tight junctions
What provides the driving force for the diffusion of Cl- into the cell at the 2nd half of the PT?
High [Cl-] in the tubular fluid
How is glucose reabsorption in the 2nd half of the PT different from the first 1/2?
Still Na+/glucose symport, but now 2x Na+ required per glucose, still facilitated diffusion to leave the basolateral side
Would you find an NKP on the basolateral side of the 2nd half of the PT?
What other transporter involving K+ would you find there?
- K+ Cl- symporter (both out, using K+ gradient from NKP)
How is water concentration related to osmolality?
Increased [H2O], decreased osmolality (and vice versa)
Can H2O follow Na+ transcellularly, paracellular, or both?
Besides Na+, what other things can H2O follow to be reabsorbed in the PT?
Cl-, organic solutes
Explain solute (solvent?) drag.
H2O highly concentrated in ISF; its hydrostatic pressure pushes H2O into caps, and solutes/ions follow (especially K+ and Ca2+)
Normally, what % of proteins are reabsorbed at the PT?