Diuretics

Question 1

The proximal tubule is permeable to what?

Answer 1

Water and sodium

Question 2

Which side exchanges sodium for potassium and via what?

Answer 2

Basal (blood) end, via sodium potassium ATPase

Question 3

Which pressure from the blood acts to reabsorb water?

Answer 3

Oncotic pressure

Question 4

How do glucose and amino acids get reabsorbed and where?

Answer 4

Coupled to sodium transport, in PCT

Question 5

How does bicarbonate get reabsorbed in the PCT?

Answer 5

Carbonic anhydrase converts hydrogen ions and HCO3- to CO2 and water in the lumen. These are taken into the cell. The same enzyme does the reverse reaction. The bicarbonate produced is coupled with sodium and is reabsorbed into the blood.

Question 6

What moves from the blood to the lumen in the PCT?

Answer 6

Exogenous agents

Question 7

Which limb is permeable to water?

Answer 7

Descending limb only

Question 8

Which transporter exists on the apical side of the ascending limb?

Answer 8

Sodium chloride potassium triple transporter

Question 9

Which main ions are reabsorbed in the ascending limb of the loop of Henle?

Answer 9

Sodium and chloride

Question 10

What is the countercurrent effect?

Answer 10

Concentrated interstitium in comparison to loop of Henle, as sodium can move out of ascending limb, but not the descending limb, so the interstitium becomes more concentrated in comparison to the tubule

Question 11

Which transporter exists in the early distal tubule?

Answer 11

Sodium chloride transporter

Question 12

Which part of the kidney is aldosterone sensitive?

Answer 12

Late distal tubule

Question 13

Describe the water movement via distal tubule.

Answer 13

Impermeable to water in early distal tubule due to tight junctions between cells and lack of transport proteins.
Unless there aquaporins in the later distal tubule it can’t move through.

Question 14

What is the effect of the countercurrent effect?

Answer 14

Enables osmotic gradient for reabsorption of water in the late distal tubule and collecting duct

Question 15

Explain how and where osmotic diuretics work. Give an example.

Answer 15

Mannitol - increases osmolality of tubular fluid therefore decreases concentration gradient between tubule and interstitium, therefore water reabsorption decreased

Question 16

Which transporter is blocked by loop diuretics and where? What is the effect of this?

Answer 16

Triple transporter of ascending limb. Interferes with counter current effect.

Question 17

What is a side effect of loop diuretics and why?

Answer 17

Normally some potassium is recycled back to the lumen, which drives paracellular movement of calcium and magnesium. Loss of this means these ions are lost.

(Decreases positive lumen potential)

Question 18

Why is potassium lost due to loop diuretics?

Answer 18

Increased delivery of sodium to later parts of the tubule means that the body tries to reabsorb it in exchange for potassium.

Question 19

Which transporters are inhibited by thiazide diuretics and where does this happen?

Answer 19

Sodium chloride transporter at distal convoluted tubule

Question 20

What three side effects result from thiazide diuretics?

Answer 20

Hypokalemia (in exchange for sodium at later parts of the tubule)
Magnesium loss
Calcium reabsorption

Question 21

Low tubular sodium normally stimulates renin. Yet renin secretion increases as a result of diuretics. Why?

Answer 21

Reduced renal perfusion pressure stimulates the macula densa cell.

Question 22

Which diuretic activates the renin secretion quite badly?

Answer 22

Loop diuretics, due to blockage of triple transporter which also signals to macula densa cell?

Question 23

What is given to counteract renin production with diuretics?

Answer 23

ACE Inhibitors

Question 24

Name two classes of potassium sparing diuretics

Answer 24

Aldosterone receptor antagonists

Inhibitors of aldosterone sensitive sodium channels

Question 25

What does spironolactone do?

Answer 25

Blocks MR, therefore blocks sodium channel insertions and sodium potassium ATPase. Therefore spares potassium.

Question 26

Explain how amiloride works

Answer 26

Prevents sodium channels at apical side

Question 27

Give the side effects of both thiazides and loops and explain why

Answer 27

Hyponatremia
Hypovolemia
Hypokalemia
Metabolic alkalosis 
Hyperuricemia

Question 28

Why is a side effect hyperuricemia?

Answer 28

Thiazides and loops compete with uric acid for the organic anion transporter, which moves these molecules from the blood into the tubule.

Question 29

Which diuretic is commonly used to treat hypertension?

Answer 29

Thiazide diuretics

Question 30

Why is thiazide not so great?

Answer 30

Initial response decreases within four to six weeks

Question 31

What other beneficial effect do thiazides have, long term, and why ?

Answer 31

Vasodilatory effect:
Activation of eNOS
Ca channel antagonism
Hyperpolarisation of SM cells via K+

Question 32

Which heart condition is loop diuretics used for?

Answer 32

Heart failure (to get rid of congestion)

Question 33

What is a complication of using loops for this heart condition? How can you prevent this?

Answer 33

Renin production

Can be controlled by ACE inhibition or potassium sparing diuretics