L28 - kidney: urine pH & drug removal

Question 1

3 possible routes for substances entering nephron

Answer 1

1. fully excreted
2. partially excreted
3. not excreted

Question 2

explain route where substances would be fully excreted when entering nephron

Answer 2

• partially filtered
• mostly secreted
  all substance leaves via urinary excretion

Question 3

explain route where substances would be partially excreted when entering nephron

Answer 3

• partially filtered
• partially reabsorbed
• partially excreted

Question 4

explain route where substances would not be excreted when entering nephron

Answer 4

• partially filtered
• fully reabsorbed
• not excreted

Question 5

equation to find amount excreted?

Answer 5

amount excreted = amount filtered + amount secreted - amount reabsorbed

Question 6

factors affecting the renal processing of substances

Answer 6

• degree substance is filtered
• degree that is reabsorbed
• degree that is secreted

Question 7

what is proteinuria?

Answer 7

high levels of protein in urine

Question 8

proteins in the kidney

Answer 8

• whole proteins and protein based drugs are not excreted by kidneys
• exception in cases of bad kidney function

Question 9

how do the kidneys regulate blood and urine pH?

Answer 9

• carbonic anhydrase enzyme converts CO2 + H2O into carbonic acid which dissociates to form HCO3- and H+
• kidney regulates carbonate so also pH

Question 10

describe carbonate reabsorption

Answer 10

1. carbonic acid created in tubule cells breaks down into HCO3- & H+
2. H+ transported into tubules and combines with filtered HCO3- to form carbonic acid
3. HCO3- transported into blood to body
4. so net result: no loss of HCO3-

Question 11

describe carbonate generation - H+ secretion

Answer 11

1. carbonic acid generated in tubular cells
2. H+ combines with filtered HPO42- and is excreted
3. HCO3- transported into body
4. net result = gain of HCO3-

Question 12

carbonate generation - glutamine metabolism

Answer 12

1. a.a glutamine enters tubule cells from filtrate (tubule) or the blood plasma (interstitial space)
2. glutamine is metabolised inside the cell to NH4+ and HCO3-
3. ammonia secreted into tubules + excreted
4. HCO3- transported into body
5. net result: gain of HCO3-

Question 13

regulation of body pH

Answer 13

• tightly balanced as processes dependent on pH
• loss of H+, pH inc, alkalosis
• gain H+, acidosis

Question 14

response to acidosis

Answer 14

1. lots of H+ secreted into tubules from tubule cells
2. all filtered HCO3- is reabsorbed
3. excess carbonate is absorbed as H+ excreted bound to phosphate
4. glutamine metabolism enhanced generating more HCO3-

Question 15

response to alkalosis

Answer 15

1. H+ secreted into tubules can’t keep up with filtered HCO3-
2. so excess HCO3- excreted
3. glutamine metabolism decreased reducing HCO3- generation

Question 16

role of urine pH in drug excretion (acidic + alkaline urine)

Answer 16

• most drugs are weak acids/bases
• in alkaline urine, acidic drugs are ionised
• in acidic urine, alkaline drugs are ionised
• ionised drugs are less likely to be reabsorbed, so increased secretion

Question 17

what needs to happen in aspirin poisoning?

Answer 17

1. aspirin needs to be quickly removed from body
2. IV infusion of sodium bicarbonate
3. carbonate enters urine, raises pH
4. aspirins active metabolite salicylic acid becomes ionised, reducing its reabsorption
5. so aspirin is excreted quicker, lowering plasma conc