Diuretics

Question 0

Summarise the main classes of diuretics and their mechanisms of action

Answer 0

Loop diuretics - block NaKCC transporter on apical membrane, calcium and magnesium not reabsorbed
Thiazide diuretics - block NaCl transporter in DCT
Potassium sparing/aldosterone antagonist - reduce Na+ channel activity, reduce loss of K+ on late distal tubule and collecting duct
Carbonic anhydrase inhibitor - act on proximal tubule (brush border), loss of HCO3- in urine
Osmotic diuretics - increased filtrate and plasma osmolarity, loss of water, sodium and potassium in urine

Question 1

What is a diuretic?

Answer 1

A substance/drug that promotes a diuresis due to increased renal excretion of sodium and water

Question 2

Describe some adverse effects of diuretic use and abuse

Answer 2

Thiazide diuretics - beware of hypokalaemia
Potassium sparing/aldosterone antagonist - beware of hyperkalaemia
Carbonic anhydrase - beware metabolic acidosis
Hepatic encephalopathy

Question 3

Describe the object of diuretic therapy and some conditions in which diuretics are used

Answer 3

Object - decreases ECF volume, reduce oedema
Conditions - congestive heart failure, nephrotic syndrome, liver cirrhosis, kidney failure, acute pulmonary oedema (left heart failure), hypertension, primary hyperaldosteronism (Conn’s syndrome)

Question 4

Describe how diuretics work

Answer 4

Direct action on cells - block Na+ transporters
Antagonising action of aldosterone
Modification of filtrate content
Inhibiting activity of carbonic anhydrase enzyme