Physiology of Acid Base Balance

Question 1

What is the normal range for plasma pH?

Answer 1

7.35-7.4

Question 2

What is the normal range for plasma HCO3 conc?

Answer 2

23-27

Question 3

What is the normal range for arterial PCO2?

Answer 3

35-45

Question 4

What does compensation mean?

Answer 4

pH restored back to 7.4

Question 5

What does correction mean?

Answer 5

both pH and HCO3 back to normal

Question 6

What are the immediate buffers in the body?

Answer 6

blood buffers - haemaglobin and HCO3
buffers in the ECF - HCO3

these stores can get depleted

Question 7

What causes respiratory acidosis?

Answer 7

retention of CO2 - chronic bronchitis and emphysema, respiratory depression, chest injuries, airway obstruction

Question 8

How is respiratory acidosis compensated?

Answer 8

PCO2 drives H secertion by the kidney so CO2 retention stimulates H secretion into the filtrate which generates titratable acid and NH4
All filtered HCO3 is reabsorbed so the plasma conc rises

Question 9

How is respiratory acidosis corrected?

Answer 9

restoring normal ventilation to lower PCO2

Question 10

What causes respiratory alkalosis?

Answer 10

excessive removal of CO2 from the body due to low inspired PO2 at altitude - hypoxia stimulates peripheral chemoreceptors and hyperventilation lowers PCO2
or hysterical over breathing and hyperventilation

Question 11

How is respiratory alkalosis compensated?

Answer 11

excessive removal of CO2 reduces H secretion into the tubule therefore H secretion is insufficient to absorb the filtered HCO3 so then HCO3 is secreted into the urine as alkaline

Question 12

What causes metabolic acidosis?

Answer 12

excess H from ingestion of acids or acid containing foods, excessive metabolic production of H (lactic acid during exercise), excessive loss of base from the body (diarrhoea)

Question 13

How is metabolic acidosis compensated?

Answer 13

decrease in plasma pH stimulates peripheral chemoreceptors which stimulate ventilation

Question 14

How is metabolic acidosis corrected?

Answer 14

H secretion continues and produces TA and NH4 to generate more HCO3, acid is excreted in the urine so HCO3 is restored

Question 15

What causes metabolic alkalosis?

Answer 15

excessive H loss from the body due to vomiting (loss of HCl from the stomach), ingestion of alkali and alkali containing foods
aldosterone hyper secretion - causes acid secretion

Question 16

How is metabolic alkalosis compensated?

Answer 16

increased pH slows ventilation through chemoreceptors, plasma H rises which lowers pH, HCO3 rises aswell

Question 17

How is metabolic alkalosis corrected?

Answer 17

filtered HCO3 load is so large compared to normal that not all the filtered HCO3 is reabsorbed
HCO3 is excreted in the urine as alkaline