16 Acid base balance

Question 1

Which sites are involved in acid-base balance? (4)

Answer 1

Lungs, kidney, GI tract, liver.

Question 2

How does haemoglobin regulate release O2 in the peripheral tissues?

Answer 2

CO2 is taken in, broken down to HCO3- and H+. Red blood cell is acidified. HbO2 releases oxygen.

Question 3

How is haemoglobin involved in excretion of CO2 in the lungs?

Answer 3

O2 is captured by haem forming HbO2. Released H+ binds to HCO3-, releasing CO2.

Question 4

What makes the oxygen-haem curve shift to the right? (3)

Answer 4

Increased 2,3 diPG.
Acidosis.
Increased temperature.

Question 5

What happens to haemoglobin with right shift of the O2-haem curve?

Answer 5

Haem is less capable of carrying oxygen - more is deposited in the tissues.

Question 6

How do the kidneys reclaim bicarbonate?

Answer 6

Active Na/H pump (H+ into tubule). H+ converts HCO3- to H2CO3. Dissociates to form CO2 which is reclaimed. (forms bicarbonate in the tissues).

Question 7

What effect does aldosterone have on the kidney?

Answer 7

Acts on K+/H+ exchange (both compete for excretion in distal tubules) in return for Na+.
If acidotic, H+ is lost in distal tubules.

Question 8

What role does the GI tract play in acid-base metabolism? (2)

Answer 8

Stomach excretes H+.

Pancreas excrete HCO3-.

Question 9

What role does the liver play in acid-base metabolism? (2)

Answer 9

Dominant site of lactate metabolism.

Only site of urea synthesis.

Question 10

How is the urea cycle involved in acid-base metabolism?

Answer 10

Acidosis inhibits urea formation because it uses HCO3- (which when retained alkalises the blood).
Alkalosis stimulates ammonium (NH4) to ammonia (NH3) conversion, (H+ retention acidifies the blood).

Question 11

What are the causes of metabolic acidosis? (4)

Answer 11

Increased H+ formation.
Acid ingestion.
Reduced renal H+ excretion.
Bicarbonate loss.

Question 12

What are the blood gas readings for metabolic acidosis? (3)

Answer 12

Increased H+.
Increased pO2.
Decreased CO2. (Respiratory compensation).

Question 13

What are the causes of metabolic alkalosis? (3)

Answer 13

Gastric bicarbonate production.
Renal HCO3- generation in hypokalaemia. (H+ excreted as no competition, increases HCO3- reclamation).
Administration of bicarbonate.

Question 14

What are the blood gas readings in metabolic alkalosis? (3)

Answer 14

Decreased H+.
Increased CO2.
Decreased pO2. (Respiratory suppression).

Question 15

What are the causes of respiratory acidosis? (3)

Answer 15

CO2 retention due to:
inadequate ventilation
parenchymal lung disease
inadequate perfusion

Question 16

What are the blood gas readings in respiratory acidosis? (3)

Answer 16

Increased H+.
Increased CO2.
Decreased O2.

Question 17

What is the cause of respiratory alkalosis?

Answer 17

Increased CO2 excretion due to excessive ventilation.

Question 18

Wha are the blood gas readings in respiratory alkalosis? (3)

Answer 18

Decreased H+.
Decreased CO2.
Increased O2.

Question 19

What are the causes of increased H+ formation? (4)

Answer 19

Ketoacidosis: alcoholic or diabetic.
Lactic acidosis.
Poisoning.
Inherited organic acidaemias.

Question 20

How does diabetic keto-acidosis arise?

Answer 20

Hyperglycaemia causes osmotic diuresis and pre renal uraemia.
Hyperketonaemia leads to increased FFA levels in the blood - broken down to acids.

Question 21

What are the causes of lactic acidosis?

Answer 21

Shock.

Metabolic and toxic causes.

Question 22

Why does acidosis occur in alcoholics?

Answer 22

Thiamine deficiency affects pyruvate dehydrogenase, increasing lactic acid levels.
Profuse vomiting.
Ketoacidosis secondary to counter-regulatory hormones.

Question 23

Why does renal failure result in metabolic acidosis? (2)

Answer 23

Increased bicarbonate loss.

Reduced NH4 excretion - goes to liver for urea synthesis.