Acid base

Question 1

Why is hypokalemia associated with metabolic alkalosis?

Answer 1

Low K+ causes K+ to move out of cells into interstitial space. This makes the cell electronegative and thus H+ move into cell reducing acid- alkalosis.
K+ and H+ also compete for secretion in the distal tubule. If there is less K+ more H+ can diffuse into distal tubule cell and be lost -alkalosis

Question 2

Describe the anion gap

Answer 2

Only useful in metabolic acidosis. Reflects the difference in cations and anions. Normal range is 14-18. In metabolic acidosis the anion gap is increased to reflect the increase in acidotic stuff (lactate, ketones, phosphate/sulfate, poisons)

Question 3

Describe base excess

Answer 3

The amount of acid or base needed to restore a pH to 7.4. Normal is 0 (-2 to +2)

Question 4

If base excess is positive is it metabolic acidosis or alkalosis?

Answer 4

Metabolic alkalosis (more base less acid)

Question 5

If base excess is negative is it metabolic acidosis or alkalosis

Answer 5

Metabolic acidosis (less base more acid)

Question 6

Describe normal anion gap acidosis

Answer 6

Whereby there are defects in acid excretion rather than a excess in other anions (e.g. lactate). This can occur in renal tubular acidosis where the H+/K+ exchanger in the distal tubule does not work properly and H+ accumulates in the body and K+ is lost (hypokalaemia). Also can occur in any pathology that effects aldosterone

Question 7

In acidosis if the urine pH is >5.5 (more alkalotic) what does this suggest

Answer 7

Renal tubular acidosis

Question 8

Is acidosis associated with hyperkalaemia or hypokalaemia

Answer 8

Hyperkalaemia. In acidosis H+ moves down its concentration gradient into the cells causing K+ to move out into blood.

Question 9

Is alkalosis associated with hyper or hypokalaemia?

Answer 9

Hypokalaemia

Question 10

What are the exceptions to the hyperkalaemia-acidosis/ hypokalaemia-alkalosis rule

Answer 10

Diarrhoea- HCO3- plus K+ loss (hypokalaemia)

Renal tubular acidosis- (hypokalaemia)

Question 11

Describe three mechanisms that the kidneys have for correcting acidaemia

Answer 11

1) producing new HCO3- through metabolising glutamine to NH4+ and HCO3-
2) HCO3- joins with H+ in lumen to form carbonic acid (H2CO3). Carbonic anydrase (brush border enzyme) converts H2CO3 into H20 and C02 which can freely diffuse into proximal tubule cell. CA then transforms the H2O and CO2 into carbonic acid which disassociates into HCO3- and H+. The HCO3- can then cross the basolateral border through channels.
3) secretion of H+ through combing it with NH3 which cannot diffuse into lumen into NH4+ which can. This is then excreted in urine.