Acid-base Homeostasis

Question 1

What buffering systems are in place?

Answer 1

• Haemoglobin
• Bicarbonate
• Proteins
• Phosphate
• Ammonia
• Misc organic acids

Question 2

Where are the sites of acid-base metabolism?

Answer 2

• Lungs
• Kidneys
• GI tract
• Liver

Question 3

What causes a RIGHT shift O2 haemoglobin dissociation curve?

Answer 3

• Temperature
• Acidosis
• Increased 2,3 diPG

Question 4

Describe acid-base and the liver (what is it the only site of and dominant site of?)

Answer 4

• Dominant site of lactate metabolism

- Only site of urea synthesis

Question 5

How are proteins and amino acids metabolised in the liver?

Answer 5

proteins & amino acids–> carbon skeleton or NH4+

NH4+—–> NH3 excreted in urine stimulated by alkalosis

Carbon skeleton—-> H2O + CO2 + HCO3- —> H+ + urea inhibited by acidosis

Question 6

What happens in severe liver failure?

Answer 6

• Metabolic alkalosis
• NH4+ toxicity
• Production of urea and H+

Question 7

What happens in compensatory mechanisms?

Answer 7

• Respiratory
• Renal bicarbonate regeneration
• hepatic shift between urea synthesis and ammonia excretion
• Range 36-44

Question 8

What happens in metabolic acidosis?

Answer 8

• Increased H+ formation
• Acid ingestion
• Reduced renal H+ excretion
• Loss of bicarbonate
• Increased pO2
• Decreased pCO2
• Tiredness and weight loss

Question 9

What happens in metabolic alkalosis?

Answer 9

• Generation of bicarbonate by gastric mucosa
• Renal generation of HCO3- in hypokalaemia
• Administration of bicarbonate
• Decrease H+ and pO2
• Increased pCO2

Question 10

What are the consequences of metabolic alkalosis?

Answer 10

• K+= cells and urine
• PO4 = cells
• Respiratory suppression
• Vomiting (epigastric pain & dyspepsia)
• Weakness in upper and lower limbs

Question 11

What happens in respiratory acidosis?

Answer 11

-CO2 retention due to:
inadequate ventilation
parenchymal lung disease
inadequate perfusion
-Increased H+ and pCO2
-Decreased pO2

Question 12

What happens in respiratory alkalosis?

Answer 12

• Increased CO2 excretion due to excessive ventilation
• Decreased H+ and pCO2
• Increased pO2
• CO2 excretion > CO2 production

Question 13

What are causes of metabolic acidosis?

Answer 13

• Increased H+ formation
• Acid ingestion
• Reduced renal H+ excretion
• Loss of bicarbonate

Question 14

Increased H+ formation leads to?

Answer 14

• Ketoacidosis (diabetic/alcoholic)
• Lactic acidosis
• Poisoning
• Inherited organic acidoses

Question 15

What happens in diabetic kept-acidosis?

Answer 15

• Hyperglycaemia
• Osmotic diuresis –> pre-renal uraemia
• Hyperketonaemia
• Increased FFA

Question 16

What are the two types of lactic acidosis?

Answer 16

Type a = Shock

Type b = Metabolic & toxic causes

Question 17

Describe acidosis in an alcoholic?

Answer 17

• NAD+ depletion
• Thiamine deficiency (PDH co-factor)
• Enhanced glycolysis for ATP formation
• Keto-acids (beta-HBD) to counter regulatory hormones
• Profuse vomiting

Question 18

Does high lactate mean lactic acidosis… in alkalosis?

Answer 18

In alkalosis

1) increased glycolysis
2) reduced O2 delivery due to shift in O2 dissociation curve
3) Lactate induced vasoC
4) impaired mitochondrial respiration

Question 19

Does high lactate mean lactic acidosis.. in O2 debt?

Answer 19

• further anaerobic lactate production

- Hyperventilation

Question 20

Reduced H+ excretion means?

Answer 20

• Renal tubular acidosis

- Generalised renal failure

Question 21

What happens in renal failure?

Answer 21

• Reduced volume of nephrons
• Increased bicarbonate loss
• Reduced NH4+ excretion
• NH4+ to liver for urea and H+ synthesis
• Only fraction of NH4+ derived from glutamine