ChemPath: Acid-Base Handling

Question 1

What is the normal range for H+ concentration? What is normal pH

Answer 1

35-45 nmol/L in ECF

pH 7.35-7.45

Question 2

What equation links H+ concentration to pH?

Answer 2

pH = log1/[H+]

Question 3

What are the three main physiological buffers?

Answer 3

• Bicarbonate (ECF, renal tubular fluid)
• Haemoglobin (RBC)
• Phosphate (renal tubular fluid/intracellular)

NOTE: also protein and bone

Question 4

What is the rate of production of H+ ions per day?

Answer 4

50 - 100 mmol/day

Question 5

Describe how the kidneys excrete H+ ions. Where does this occur?

Answer 5

Via bicarbonate through the production of carbonic acid
Occurs in proximal tubules

Question 6

Describe how H+ ions pass through the renal epithelial membrane.

Answer 6

H+ ions cannot pass through the membrane itself so a transport system is necessary (Na+/H+ transporter)

Question 7

What is the rate of production of carbon dioxide per day?

Answer 7

20,000-25,000 mmol/day

Question 8

Describe the relationship between CO2 and repiratory rate

Answer 8

• Respiration is controlled by chemoreceptors in the hypothalamic respiratory centre
• An increase in CO2 will stimulate an increase in ventilation which then brings down CO2 concentration

Question 9

What information is provided by ABGs?

Answer 9

• pO2
• pCO2
• pH

Question 10

What are 3 mechanism of in metabolic acidosis?

Answer 10

Caused by:

• Increased H+ production (e.g. DKA)
• Decreased H+ excretion (e.g. renal tubular acidosis)
• Bicarbonate loss (e.g. diarrhoea)

Question 11

What are 3 mechanisms of respiratory acidosis?

Answer 11

Caused by:

• Decreased ventilation
• Poor lung perfusion
• Impaired gas exchange

NOTE: metabolic compensation is slower than respiratory compensation

Question 12

What happens in chronic respiratory acidosis?

Answer 12

Metabolic compensation will drive H+ down to near normal range, however pCO2 and bicarbonate will remain elevated

Question 13

What are 3 mechanisms of metabolic alkalosis?

Answer 13

Caused by:

• H+ loss (e.g. pyloric stenosis)
• Hypokalaemia
• Ingestion of bicarbonate

Question 14

What is the main mechanism behind respiratory alkalosis, and what are 3 causes?

Answer 14

Main mechanism is hyperventilation, which can be due to:

• Voluntary
• Artificial ventilation
• Stimulation of the respiratory centre

Question 15

What derangement of acid-base balance would be caused by pyloric stenosis?

Answer 15

Metabolic alkalosis due to loss of H+ from profuse vomiting

Question 16

Which condition classically causes a mixed respiratory alkalosis and metabolic acidosis?

Answer 16

• Aspirin overdose
• Aspirin causes high anion gap metabolic acidosis whilst simulataneously causing respiratory alkalosis by stimualting the respiratory centre