Acid-base Homeostasis Flashcards
What buffering systems are in place?
- Haemoglobin
- Bicarbonate
- Proteins
- Phosphate
- Ammonia
- Misc organic acids
Where are the sites of acid-base metabolism?
- Lungs
- Kidneys
- GI tract
- Liver
What causes a RIGHT shift O2 haemoglobin dissociation curve?
- Temperature
- Acidosis
- Increased 2,3 diPG
Describe acid-base and the liver (what is it the only site of and dominant site of?)
- Dominant site of lactate metabolism
- Only site of urea synthesis
How are proteins and amino acids metabolised in the liver?
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
What happens in severe liver failure?
- Metabolic alkalosis
- NH4+ toxicity
- Production of urea and H+
What happens in compensatory mechanisms?
- Respiratory
- Renal bicarbonate regeneration
- hepatic shift between urea synthesis and ammonia excretion
- Range 36-44
What happens in metabolic acidosis?
- Increased H+ formation
- Acid ingestion
- Reduced renal H+ excretion
- Loss of bicarbonate
- Increased pO2
- Decreased pCO2
- Tiredness and weight loss
What happens in metabolic alkalosis?
- Generation of bicarbonate by gastric mucosa
- Renal generation of HCO3- in hypokalaemia
- Administration of bicarbonate
- Decrease H+ and pO2
- Increased pCO2
What are the consequences of metabolic alkalosis?
- K+= cells and urine
- PO4 = cells
- Respiratory suppression
- Vomiting (epigastric pain & dyspepsia)
- Weakness in upper and lower limbs
What happens in respiratory acidosis?
-CO2 retention due to: inadequate ventilation parenchymal lung disease inadequate perfusion -Increased H+ and pCO2 -Decreased pO2
What happens in respiratory alkalosis?
- Increased CO2 excretion due to excessive ventilation
- Decreased H+ and pCO2
- Increased pO2
- CO2 excretion > CO2 production
What are causes of metabolic acidosis?
- Increased H+ formation
- Acid ingestion
- Reduced renal H+ excretion
- Loss of bicarbonate
Increased H+ formation leads to?
- Ketoacidosis (diabetic/alcoholic)
- Lactic acidosis
- Poisoning
- Inherited organic acidoses
What happens in diabetic kept-acidosis?
- Hyperglycaemia
- Osmotic diuresis –> pre-renal uraemia
- Hyperketonaemia
- Increased FFA
What are the two types of lactic acidosis?
Type a = Shock
Type b = Metabolic & toxic causes
Describe acidosis in an alcoholic?
- NAD+ depletion
- Thiamine deficiency (PDH co-factor)
- Enhanced glycolysis for ATP formation
- Keto-acids (beta-HBD) to counter regulatory hormones
- Profuse vomiting
Does high lactate mean lactic acidosis… in alkalosis?
In alkalosis
1) increased glycolysis
2) reduced O2 delivery due to shift in O2 dissociation curve
3) Lactate induced vasoC
4) impaired mitochondrial respiration
Does high lactate mean lactic acidosis.. in O2 debt?
- further anaerobic lactate production
- Hyperventilation
Reduced H+ excretion means?
- Renal tubular acidosis
- Generalised renal failure
What happens in renal failure?
- 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
