16 Acid base balance Flashcards
Which sites are involved in acid-base balance? (4)
Lungs, kidney, GI tract, liver.
How does haemoglobin regulate release O2 in the peripheral tissues?
CO2 is taken in, broken down to HCO3- and H+. Red blood cell is acidified. HbO2 releases oxygen.
How is haemoglobin involved in excretion of CO2 in the lungs?
O2 is captured by haem forming HbO2. Released H+ binds to HCO3-, releasing CO2.
What makes the oxygen-haem curve shift to the right? (3)
Increased 2,3 diPG.
Acidosis.
Increased temperature.
What happens to haemoglobin with right shift of the O2-haem curve?
Haem is less capable of carrying oxygen - more is deposited in the tissues.
How do the kidneys reclaim bicarbonate?
Active Na/H pump (H+ into tubule). H+ converts HCO3- to H2CO3. Dissociates to form CO2 which is reclaimed. (forms bicarbonate in the tissues).
What effect does aldosterone have on the kidney?
Acts on K+/H+ exchange (both compete for excretion in distal tubules) in return for Na+.
If acidotic, H+ is lost in distal tubules.
What role does the GI tract play in acid-base metabolism? (2)
Stomach excretes H+.
Pancreas excrete HCO3-.
What role does the liver play in acid-base metabolism? (2)
Dominant site of lactate metabolism.
Only site of urea synthesis.
How is the urea cycle involved in acid-base metabolism?
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).
What are the causes of metabolic acidosis? (4)
Increased H+ formation.
Acid ingestion.
Reduced renal H+ excretion.
Bicarbonate loss.
What are the blood gas readings for metabolic acidosis? (3)
Increased H+.
Increased pO2.
Decreased CO2. (Respiratory compensation).
What are the causes of metabolic alkalosis? (3)
Gastric bicarbonate production.
Renal HCO3- generation in hypokalaemia. (H+ excreted as no competition, increases HCO3- reclamation).
Administration of bicarbonate.
What are the blood gas readings in metabolic alkalosis? (3)
Decreased H+.
Increased CO2.
Decreased pO2. (Respiratory suppression).
What are the causes of respiratory acidosis? (3)
CO2 retention due to:
inadequate ventilation
parenchymal lung disease
inadequate perfusion
What are the blood gas readings in respiratory acidosis? (3)
Increased H+.
Increased CO2.
Decreased O2.
What is the cause of respiratory alkalosis?
Increased CO2 excretion due to excessive ventilation.
Wha are the blood gas readings in respiratory alkalosis? (3)
Decreased H+.
Decreased CO2.
Increased O2.
What are the causes of increased H+ formation? (4)
Ketoacidosis: alcoholic or diabetic.
Lactic acidosis.
Poisoning.
Inherited organic acidaemias.
How does diabetic keto-acidosis arise?
Hyperglycaemia causes osmotic diuresis and pre renal uraemia.
Hyperketonaemia leads to increased FFA levels in the blood - broken down to acids.
What are the causes of lactic acidosis?
Shock.
Metabolic and toxic causes.
Why does acidosis occur in alcoholics?
Thiamine deficiency affects pyruvate dehydrogenase, increasing lactic acid levels.
Profuse vomiting.
Ketoacidosis secondary to counter-regulatory hormones.
Why does renal failure result in metabolic acidosis? (2)
Increased bicarbonate loss.
Reduced NH4 excretion - goes to liver for urea synthesis.
