Acid/Base

Question 1

What are the two urinary acid buffers?

Answer 1

HPO4
NH3 (metabolic acidosis causes release of glutamine from muscle cells)

Question 2

Name the channel that reabsorbs bicarbonate in the following nephron segments:
Proximal tubule?
Loop of Henle?
Distal tubule?
Collecting duct?

Answer 2

Proximal tubule = Na/3HCO3 symporter

Loop of Henle = Cl/HCO3 antiporter

Distal tubule = Cl/HCO3 antiporter

Collecting duct = Cl/HCO3 antiporter

Question 3

What stimulates the Na/H antiporter to release H+ into the proximal tubular lumen for CAIV to create CO2 and H2O?

Answer 3

Metabolic acidosis

Question 4

How can the urine osmolar gap be used in the evaluation of RTA?

Answer 4

< 150 mean kidneys are not making enough ammonium (suggestive of RTA I of RTA IV)

Question 5

How can the urine anion gap be used in evaluation of acidosis?

Answer 5

+ = kidney not making enough ammonium (RTA)

• = kidney is making enough ammonium

Question 6

In what clinical situations is a urine anion gap calculation inaccurate?

Answer 6

Urine Na+ < 20

Lactic acidosis

Question 7

How is RTAI associated with kidney stones?

Answer 7

Acidosis causes
- release of CaCO3 from bones
- proximal tubule uptake of citrate

Question 8

Describe the mechanism of RTAI with the following:
Amphotericin?
Trimethoprim?
SLE/Sjogrens?

Answer 8

Amphoterecin = disrupted intercalated cell membrane

Trimethoprim = ENaC inhibition

SLE/Sjogrens = Absent H+ATPases

Question 9

Describe the mechanism of RTAIV with the following:
Diabetes mellitus?
NSAIDs?

Answer 9

Diabetes mellitus = Nerve damage prevents conversion of prorenin into renin

NSAIDs = Block release of renin from juxtaglomerular cells

Question 10

How can potassium disorders affect renal ammonium production?

Answer 10

Hyperkalemia decreases proximal tubule ammonium production
Hypokalemia increases proximal tubule ammonium production

Question 11

What is the expected PCO2 in metabolic alkalosis?

Answer 11

PCO2 = [0.7 * (HCO3 - 24)] + 40 +/- 2

Question 12

Ingestion of what toxin results in a normal anion gap?

Answer 12

Isopropyl alcohol

Question 13

What acid base abnormality can be seen with sodium thiosulfate use?

Answer 13

Metabolic acidosis

Question 14

Toluene is associated with what acid base abnormality?

Answer 14

Anion gap + non-anion gap metabolic acidosis

Question 15

Use the pH formula to understand how 0.9% NaCl can cause acidosis?

Answer 15

pH = [HCO3] / pCO2

Question 16

List the three reasons why metabolic alkalosis can occur with diuretic use?

Answer 16

1) Increase distal Na+ delivery and subsequent H+ secretion
2) Volume depletion and AngII mediated proximal HCO3- reabsorption
3) Chloride depletion and decreased pendrin mediated HCO3- secretion

Question 17

What is the corrected bicarbonate formula?

Answer 17

Corrected bicarbonate = HCO3 + (AG - 12)
Normal = 22-26
If < 22, then concurrent normal anion gap metabolic acidosis
If > 26, then concurrent metabolic alkalosis

Question 18

What is the pathophysiology of neobladder acidosis?

Answer 18

HCO3 secretion via Cl/HCO3 antiporter