Acid-Base Handling

Question 1

What is the normal range of [H+]?

Answer 1

35-45 nmol/l

Question 2

What is normal pH?

Answer 2

7.35-7.45

Question 3

How are H+ ions produced?

Answer 3

Metabolism of proteins, carbohydrates and fats produce carbon dioxide, water and hydrogen ions.

Question 4

How are H+ ions excreted?

Answer 4

Excetion by the kidney

Question 5

How much H+ is produced per day?

Answer 5

50-100 mmol/day

Question 6

What is the equation of the role of H+ within the body?

Answer 6

H+ + HCO3- H2CO3 CO2 + H2O

Question 7

What are limitations of buffering against H+?

Answer 7

ECF buffering of hydrogen is at the expense of bicarbonate.

Bicarbonate buffering of H+ is only effective in the short term.

To maintain normal homeostasis the kidney needs to excrete hydrogen ions and regenerate bicarbonate.

Question 8

How is CO2 produced?

Answer 8

Metabolism of proteins, carbohydrates and fats produce carbon dioxide, water and hydrogen ions.

Question 9

How is CO2 excreted?

Answer 9

Lungs

Question 10

How much CO2 is produced per day?

Answer 10

20,000-25,000 mmol/day

Question 11

What is CO2 production and excretion controlled by?

Answer 11

Respiration is controlled by chemoreceptors in the hypothalamic respiratory centre. In health any increase in CO2 stimulates respiration thus tending to maintain a stable concentration of CO2.

Question 12

What is metabolic acidosis?

Answer 12

Primary abnormality is increased H+ (decreased pH) with decreased bicarbonate.

Question 13

What can metabolic acidosis be due to?

Answer 13

• Increased H+ production e.g. Diabetic ketoacidosis
• Decreased H+ excretion e.g. Renal tubular acidosis
• Bicarbonate loss e.g. Intestinal fistula

Question 14

What is compensated metabolic acidosis?

Answer 14

Increase in H+ stimulates the respiratory centre.

Identified by a fall in pCO2.

H+ returns towards normal.

Question 15

What is acute respiratory acidosis?

Answer 15

Primary abnormality is increased CO2, producing increased H+ (decreased pH) and a slight increase in bicarbonate (2-4 mmol/L).

Question 16

What are causes of acute respiratory acidosis?

Answer 16

Decreased Ventilation

Poor Lung Perfusion

Impaired Gas Exchange

Question 17

What is chronic respiratory acidosis?

Answer 17

Over the course of a few days this leads to increased renal excretion of H+ combined with generation of bicarbonate. H+ may return to near normal but pCO2 and bicarbonate remain elevated.

Question 18

What is metabolic alkalosis?

Answer 18

Primary abnormality is decreased H+ (increased pH) with increased bicarbonate.

Question 19

What are causes of metabolic alkalosis?

Answer 19

H+ loss (e.g. pyloric stenosis)

Hypokalaemia

Ingestion of Bicarbonate

Question 20

What are causes of respiratory alkalosis?

Answer 20

Due to Hyperventilation

• Voluntary
• Artificial ventilation
• Stimulation of respiratory centre

Question 21

What happens in chronic respiratory alkalosis?

Answer 21

If prolonged this leads to decreased renal excretion of H+ and less bicarbonate generation. H+ may return to near normal but pCO2 and bicarbonate remain low.