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Loop Diuretics and the Ascending Limb of Henle
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1
Question
On which nephron segment is the Na+/K+/2Cl− cotransporter inhibited by loop diuretics located?
Page 34
Answer
The Na+/K+/2Cl− cotransporter inhibited by loop diuretics is located in the ascending limb of the loop of Henle.
2
Question
Which specific transporter do loop diuretics inhibit in the luminal membrane?
Page 34
Answer
Loop diuretics inhibit the Na+/K+/2Cl− cotransporter in the luminal membrane.
3
Question
What is the immediate effect of inhibiting the Na+/K+/2Cl− cotransporter on ion reabsorption?
Page 34
Answer
Inhibiting the Na+/K+/2Cl− cotransporter decreases the reabsorption of Na, K, Ca, and Mg.
4
Question
How do loop diuretics affect the reabsorption of divalent cations according to the notes?
Page 34
Answer
Loop diuretics decrease the reabsorption of divalent cations such as Ca2+ and Mg2+.
5
Question
What fraction of filtered NaCl is reabsorbed at the site where loop diuretics act?
Page 35
Answer
Approximately 25% to 30% of filtered NaCl is reabsorbed at the site where loop diuretics act.
6
Question
Why do loop diuretics have the greatest diuretic effect at their site of action?
Page 35
Answer
Loop diuretics have the greatest diuretic effect because 25%–30% of filtered NaCl are reabsorbed at that site and downstream sites are unable to compensate for the increased Na+ delivery.
7
Question
What change to the lumen electrical potential occurs when loop diuretics inhibit K+ recycling?
Page 35
Answer
Loop diuretics decrease the lumen-positive (lumen+) electrical potential that results from K+ recycling.
8
Question
What role does the lumen-positive potential normally play in the loop of Henle?
Page 35
Answer
The lumen-positive potential normally drives reabsorption of divalent cations, including Mg2+ and Ca2+, via the paracellular pathway in the loop of Henle.
9
Question
What is the effect of reducing the lumen-positive potential on Mg2+ and Ca2+ handling?
Page 35
Answer
Reducing the lumen-positive potential causes an increase in Mg2+ and Ca2+ excretion.
10
Question
What electrolyte disturbance can prolonged use of loop diuretics cause according to the notes?
Page 35
Answer
Prolonged use of loop diuretics can cause significant hypomagnesemia in some patients.
11
Question
Which membrane (luminal or basolateral) contains the Na+/K+/2Cl− cotransporter inhibited by loop diuretics as stated in the notes?
Page 34
Answer
The Na+/K+/2Cl− cotransporter inhibited by loop diuretics is located in the luminal membrane.
12
Question
List the ions whose reabsorption is decreased when the ascending limb cotransporter is inhibited.
Page 34
Answer
Reabsorption of Na+, K+, Ca2+, and Mg2+ is decreased when the ascending limb cotransporter is inhibited.
13
Question
How does K+ recycling normally contribute to the lumen-positive potential in the loop?
Page 35
Answer
K+ recycling normally generates a lumen-positive electrical potential that drives paracellular reabsorption of divalent cations in the loop of Henle.
14
Question
Why are downstream nephron segments unable to fully compensate when loop diuretics increase Na+ delivery?
Page 35
Answer
Downstream nephron segments are unable to compensate fully because a large fraction (25%–30%) of filtered NaCl is normally reabsorbed at the loop site, making compensation insufficient when that reabsorption is lost.
15
Question
According to the slide, what is the anatomical name of the nephron segment where this cotransporter acts?
Page 34
Answer
The anatomical name is the ascending loop of Henle.
16
Question
What is the primary molecular function of the Na+/K+/2Cl− symport mentioned on the slide?
Page 34
Answer
The Na+/K+/2Cl− symport mediates active reabsorption of Na+, K+, and Cl− from the lumen into the epithelial cells of the ascending loop.
17
Question
What shorthand phrase on the slide summarizes the transporter inhibited by loop diuretics?
Page 34
Answer
The shorthand phrase is 'Na+K+2Cl-symport'.
18
Question
Which ion's back diffusion contributes to the lumen-positive potential in the ascending loop according to the notes?
Page 35
Answer
Back diffusion of K+ into the lumen contributes to the lumen-positive potential.
19
Question
What happens to Mg2+ excretion when the lumen-positive potential is reduced by loop diuretics?
Page 35
Answer
Mg2+ excretion increases when the lumen-positive potential is reduced by loop diuretics.
20
Question
According to the slide, which cation excretion is increased along with Mg2+ when lumen potential is reduced?
Page 35
Answer
Ca2+ excretion is increased along with Mg2+ when the lumen-positive potential is reduced.
21
Question
What term does the slide use to describe the potency of loop diuretics relative to other classes?
Page 35
Answer
The slide indicates that loop diuretics have the greatest diuretic effect at their site of action.
22
Question
What physiological consequence of inhibiting the Na+/K+/2Cl− symporter is explicitly listed on the slide?
Page 34
Answer
A decrease in reabsorption of Na, K, Ca, and Mg is explicitly listed as a consequence.
23
Question
What is the relationship between K+ recycling and divalent cation reabsorption described in the notes?
Page 35
Answer
K+ recycling creates a lumen-positive potential that normally drives paracellular reabsorption of divalent cations such as Mg2+ and Ca2+.
24
Question
What fraction range of NaCl reabsorption defines the loop of Henle's contribution as per the slide?
Page 35
Answer
The loop of Henle reabsorbs approximately 25%–30% of filtered NaCl.
25
Question
How do loop diuretics affect the lumen-positive potential that facilitates cation reabsorption?
Page 35
Answer
Loop diuretics reduce the lumen-positive potential that facilitates cation reabsorption.
26
Question
What is the clinical implication of increased Mg2+ and Ca2+ excretion with loop diuretics over time?
Page 35
Answer
A clinical implication is that prolonged use of loop diuretics can cause significant hypomagnesemia in some patients.
27
Question
Which transport process is described on the slide as being inhibited 'in the luminal membrane'?
Page 34
Answer
The Na+/K+/2Cl− cotransport process is described as being inhibited in the luminal membrane.
28
Question
What shorthand does the slide use to show the directional effect on reabsorption caused by diuretic action?
Page 34
Answer
The slide uses a down arrow (⇩) to indicate decreased reabsorption of Na, K, Ca, and Mg.
29
Question
Which two divalent cations are explicitly mentioned as having increased excretion when loop diuretics reduce the lumen potential?
Page 35
Answer
The two divalent cations are Mg2+ (magnesium) and Ca2+ (calcium).
30
Question
What mechanism described on the slide explains why loop diuretics increase excretion of Mg2+ and Ca2+?
Page 35
Answer
By decreasing the lumen-positive potential that normally drives paracellular reabsorption of Mg2+ and Ca2+, loop diuretics increase their excretion.