osmotic diuretics

Question 1

example

Answer 1

IV manitol

Question 2

why does Manintol have to be given IV

Answer 2

because it is not orally absorbed

Question 3

Manitol enters the nephron via

Answer 3

filtration but is not re-absorbed

Question 4

mechanism of action

Answer 4

increases osmolarity of the filtrate which opposes the re-absorption of water in parts of the nephron which are freely permeable to water

Question 5

major site of action of manitol

Answer 5

is the proximal convoluted tubule where most iso-osmotic reabsorption of water occurs

Question 6

what is the secondary affect of mantel

Answer 6

reduced re-absorption of sodium, because the increased volume of the filtrate reduces the concentration of sodium present which hence reduces the electrochemical gradient for sodium re-absorption

Question 7

clinical uses of IV manitol

Answer 7

raised intra-oscular and intra-cranial pressure, it does NOT actually enter the brain or the eye however, it increases the plasma osmolarity which extracts water from the brain parenchyma, CSF and aqueous humour into the plasma

Question 8

IV mantel can also be used to prevent

Answer 8

an impending pre-renal AKI caused by hypovolaemia

Question 9

adverse affects of IV manitol

Answer 9

• hyponatraemic headache

- transient expansion of the blood volume

Question 10

an osmotic diuresis can also occur

Answer 10

in hyperglycaemia, the re-absorptive capacity of the proximal convoluted tubule (via SGLT-2 AND SGLT-1) for glucose is exceeded and the glucose remaining in the filtrate retains fluid

Question 11

osmotic diuresis can also occur

Answer 11

as a conserve of using iodine based radio-contrast dye as the dye is filtered at the glomerulus but not re-absorbed causing an osmotic load