S6.1 Diuretics

Question 1

What is a diuretic?

Answer 1

A drug that promotes diuresis (increase urine) by increasing renal excretion of water and sodium, so decreases ECF volume.

Useful in conditions where Na+ and water retention cause expanded ECF volume e.g. HF, cirrhosis.

Question 2

What is the effect of aldosterone on channels?

Answer 2

Increases expression of Na+-K+-ATPase, ENaC and K+ channels

Question 3

Which diuretics work in the proximal tubule?

Answer 3

Carbonic anhydrase inhibitors and osmotic diuretics (e.g. mannitol, modifies filtrate content)

Question 4

Which diuretics work in the LoH?

Answer 4

Loop diuretics
Inhibit NaK2Cl symport
Furosemide, bumetanide

Question 5

Which diuretics work in the distal tubule?

Answer 5

Thiazides diuretics
Inhibit Na-Cl
Metolazone

Question 6

Which diuretics work in the collecting duct?

Answer 6

K+ sparing diuretics (block ENac) eg amiloride

Aldosterone antagonists (also K+ sparing) eg spironolactone

Question 7

Give some uses and adverse effects of loop diuretics

Answer 7

Uses: heart failure, pulmonary oedema, nephrotic syndrome

Adverse effects: Hypovolaemia, Ototoxicity, Alkalosis

Question 8

Give some uses and adverse effects of thiazide diuretics

Answer 8

Uses: for hypertension as they cause vasodilation

Adverse effects: gout, hyperglycaemia

Question 9

Give some uses and adverse effects of K+ sparing diuretics

Answer 9

Uses: ascites, treat hypertension caused by primary hyperaldosteronism (conn’s). Used with loop diuretics in heart failure to prevent hypokalaemia

Adverse effects: hyperkalaemia, erectile dysfunction

Question 10

Give some uses and adverse effects of carbonic anhydrase inhibitors

Answer 10

Uses: glaucoma

Adverse affects: metabolic acidosis from HCO3- loss in urine

Question 11

Give some uses of osmotic diuretics

Answer 11

Used in cerebral oedema.
Increase plasma osmolarity by drawing out fluid from tissues and cells.
Cause loss of water Na and K in urine

Question 12

Describe K+ secretion

Answer 12

In DT and CD, passive, driven by EC gradient.
Rate depends on gradient across AM and rate of Na+ absorption (inward movement of Na+ creates –ve lumen potential which is favourable for K+ secretion).

Question 13

Why do loop and thiazide diuretics cause hypokalaemia?

Answer 13

LD and TD both prevent Na absorption in the LoH and distal tubule, therefore more Na absorption occurs at the distal tubule and collecting duct.
This increased Na absorption creates a gradient for K+ secretion causing hypokalaemia.

Question 14

Name some other substances with diuretic effect

Answer 14

Alcohol (inhibits ADH)

Coffee (increases GFR, decreasing Na+ reabsorption)

Question 15

Name some diseases causing diuresis?

Answer 15

Diabetes mellitus

Nephrogenic and central diabetes insipidus - as less action from ADH