Acid-base regulation

Question 1

What is the normal physiological pH

Answer 1

7.4

Question 2

What proportions of acid are excreted by the lungs and the kidney

Answer 2

99% lungs (volatile)

1% kidney (non-volatile)

Question 3

What is the plasma H+

Answer 3

40nmol/L

Question 4

What is the normal arterial bicarbonate

Answer 4

22-26 mEg/L

Question 5

What is the role of HCO3-

Answer 5

High capacity chemical buffer that can respond rapidly to changes in metabolic acid and can be produced from volatile respiratory acid

Question 6

What is the Henderson-Hasselbach equation

Answer 6

pH = pK + log10 [HCO3-/CO2]

Question 7

Explain the process of HCO3- reabsorption in the PCT

Answer 7

1. HCO3- + H+ -> CO2 + H2O (carbonic anhydrase)
2. CO2 enters the cell -> HCO3 - + H+ (carbonic anhydrase)
   ATPases pump H+ out into the filtrate
   H+ also excreted back into the filtrate by Na+ and H+ antiporter
   HCO3- excreted into the interstitium by chloride bicarbonate exchanger and sodium bicarbonate cotransporter
   Sodium pumped out into the interstitium via sodium potassium ATPase

Question 8

Explain the process of HCO3- secretion by beta cells

Answer 8

1. CA converts CO2 + H2O -> HCO3- and H+
2. H+ pumped through the basolateral membrane into the interstitial
3. Bicarbonate pumped into the filtrate by the chloride bicarbonate exchanger

Question 9

What happens with an increase in ventilation

Answer 9

1. Increase in ventilation
2. CO2 exhaled
3. pH increases (H+ decreases)
   4 Respiratory alkalosis
4. Renal function change
5. H+ gain, HCO3- loss
6. decrease in pH

Question 10

What happens when the GI system/kidneys cause a H+ gain or HCO3- loss

Answer 10

1. decrease pH (increase H+)
2. metabolic acidosis
3. compensatory change in lung function
4. increase in ventilation
5. increased CO2 loss
6. Increase in pH

Question 11

What is the normal urine pH

Answer 11

5-9

Question 12

What is the compensatory response and mechanism for metabolic acidosis

Answer 12

Decrease paCO2

Hyperventilation to increase CO2 excretion

Question 13

What is the compensatory response and mechanism for metabolic alkalosis

Answer 13

Increase in paCO2

Hypoventilation to decrease CO2 excretion

Question 14

Where is bicarbonate absorbed in the kidney

Answer 14

80% PCT
10% loop of Henle
6% DCT
4% collecting duct

Question 15

What is the Davenport diagram and label one

Answer 15

A graphical representation of the association between pH, bicarbonate and carbon dioxide in the blood
Refer to diagram

Question 16

How much can urine proton concentration vary

Answer 16

vary more than 10,000x

Question 17

Which disturbances can coexist

Answer 17

Respiratory acidosis and respiratory alkalosis cannot coexist
Metabolic acidosis and respiratory alkalosis can coexist

Question 18

Explain the process of HCO3- generation

Answer 18

1. Glutamine splits into constituent parts
2. Ammonium excreted via NH4/Na+
3. 2 bicarbonates generated
4. Pumped into the interstitium via the chloride bicarbonate exchanger
5. Also pumped by the sodium bicarbonate costransporter
6. Sodium potassium ATPase restores K+ gradient

Question 19

How is phosphate formed in the filtrate

Answer 19

1. CA action in the cell
2. Bicarbonate/Cl- antiporter transports bicarbonate into the interstitium
3. H+ transported to the filtrate via H+ ATPase
4. H+ combines with phosphate ions to form phosphoric acid