Diuretics

Question 1

Diuresis + Diuretics

Answer 1

• Diuresis = the elimination of urine
• typically used in reference to passing of large vols of urine
• Natriuresis: is the elim of sodium ions (Na+)
• Diuretics: are drugs that increase urine vol

Diuretic therapy is used to reduce:

• blood volume
• BP (reduces load on heart)
• extracellular fluid volume (reduce edema)
• In sports may be used to lose “weight” + also used to mask other illegal drug use
• Most diuretics work by reducing Na+ (+ therefore water) (R)

Question 2

How do diuretics work to eliminate water?

1) Loop Diuretics (eg furosemide, Lasix

Answer 2

• Act at the ascending limb of LoH
• Block the Na+-K+-2Cl-symport.
• Impairs the process of generating high conc. of NaCl in renal medulla.
• reduces osmotic gradient for water (R) in CD
• less water (R) → increased urine vol

Question 3

How do diuretics work to eliminate water?

(2) Thiazide diuretics

Answer 3

• act on DCT
• inhibit the apical membrane Na+-Cl-symport
• reduces Na+ (R) → reduces osmotic “drag” for water (R) & so reduces (R) of water.
• Both loop diuretics + thiazide diuretics cause ↑K+secretion in DCT resulting in K+loss
• caused by ↑ TF vol → ↑ flow, which stimulates K+secretion

Question 4

How do diuretics work to eliminate water?

3) Potassium sparing diuretics (eg spironolactone

Answer 4

• spironolactone is an aldosterone receptor antagonist
• blocks Na+ (R) via aldosterone-sensitive Na+channel
• reduce Na+ (R) → reduces osmotic drag for water (R)
  i. e. similar to thiazides, but dif mechanism
• These diuretics block the exchange of Na+ for K+, meaning that there is reduced secretion of K+ into the nephron tubule.
• so you still get reduced Na+ (and therefore water) (R), but w/ reduced K+ secretion