Diuretics

Question 1

Describe the physiology of Na renal excretion

Answer 1

Na reabsorption from the tubule is present across most of the nephron - the proximal tubule, the loop of henle and the early and late distal convoluted tubule

Na is pumped out of the filtrate via K+ pumps that allow potassium into the filtrate

Question 2

Describe the physiology of the K renal excretion

Answer 2

K+ is important in regulating the flow of Na+ out of the filtrate

K+ pumped in typically leaves back into the interstitial space at the hoop of Henle

Alternatively, K+ in the late DCT enters into the filtrate via the sodium-potassium exchange driven by aldosterone

Question 3

Describe the physiology of H20 renal excretion

Answer 3

Water reabsorption occurs in the descending limb of the loop of Henle

the sodium reabsorption along the ascending loop of henle sets up an osmotic pressure gradient that encourages water to leave the filtrate and enter the interstitium

Question 4

Describe the physiology of the renin angiotensin-aldosterone system

Question 5

Describe the drug strategies to enhance Na and H2O excretion

Answer 5

Diuretics block Na+ from entering interstitium and therefore leaving the filtrate, this prevents the movement of H20 in turn as it produces no osmotic pressure

Aldosterone antagonists work to decrease Na+ reabsorption at the late DCT by blocking aldosterone that triggers Na+ reabsorption

Question 6

Recognise that diuretics that act late in the distal convoluted tubule also act to retain K+