Acid-Base Homeostasis Flashcards
What are the main organs that provide outputs to maintain acid-base homeostasis? (2)
- Lungs
- Kidneys
How much CO2 do you produce a day?
25mol/day.
How much unmetabolised acids do you produce a day?
50mmol/day.
How much plasma [H+] do you produce a day?
40nmol/day.
What are the main buffering systems in the body? (6)
- Haemoglobin
- Bicarbonate
- Phosphate
- Proteins
- Ammonia
- Organic acids
What is the reference range for pH?
7.35 - 7.45
What is the reference range for [H+]?
35-45 nmol/L.
How are [H+] and pH related?
As [H+] increases, pH decreases.
What is the Henderson-Hasselbalch equation used for?
- pH as a measure of acidity
- Estimates the pH of a buffer
- Finding equilibrium pH in acid-base reactions
What are the Henderson-Hasselbalch equation?
H+ + HCO3- H2CO3 CO2 + H2O
What does [H+] homeostasis require a balance between?
Balance between H+ production and regeneration of HCO3-.
What are the main sites of acid-base metabolism in the body? (4)
- Lungs
- Kidneys
- GI tract
- Liver
How long does it take for the kidneys to alter the acid-base balance?
A couple of days.
What do RBCs take up and release when acidified?
Take up CO2, release O2.
When does a right shift occur on an O2-Hb dissociation curve?
*RIGHT* Right shift with Increased 2,3 dipG H+ acidosis Temperature
What does a right shift on an O2-Hb dissociation curve mean?
RBCs cannot hold O2 as well.
-decreased SO2 at same PO2
What role does the kidney have in maintaining bicarbonate haemostasis?
Filtered by the kidneys;
- renal reclaiming (absorption by NA/H pump)
- renal regeneration
What happens at the distal tubule of the kidneys?
Endocrine control (aldosterone)»_space; regulates salt/water through K+/H+ exchange.
What happens during acidosis to K+ and H+ at the distal tubule of the kidney?
H+ is lost, K+ is retained.
How is acid-base homeostasis maintained in the GI tract?
- H+ excreted in stomach
- HCO3- excreted in pancreas to neutralise
How is the liver involved in acid-base metabolism? (2)
- Lactate metabolism
- Urea synthesis
What are proteins and AAs converted to in the liver?
- Carbon skeleton
- NH4+
What does the carbon skeleton go on the form in the liver?
H+ and urea.
-inhibited by acidosis
What does NH4+ go on too form in the liver?
NH3.
- stimulated by alkalosis
- excreted in urine
What is excess NH4+ produced by proteins used for?
Urea cycle.
-NH4+ and CO2 are combined to neutralise HCO3-
Is CO2 acidic or alkali when dissolved?
Acidic.
What pathways are blocked in severe liver failure? (2)
NH4+ + oxoglutarate»_space; glutamine.
NH4+ + CO2»_space; urea + H+.
What are the main acid-base consequences of severe liver failure? (2)
- Metabolic alkalosis
- NH4+ toxicity
What are the 2 types of acidosis/alkalosis?
- Metabolic
- Respiratory
What are the main compensatory methods for acidosis/alkalosis? (3)
- Respiratory
- Renal bicarbonate regeneration
- Hepatic shift (urea synthesis / ammonia excretion)
Is bicarbonate (HCO3-) acidic or alkaline?
Alkaline.
What is the normal [H+] value?
40 nmol/L.
range : 36-44
What is the main equation involved with alkalosis/acidosis?
H+ + HCO3- »_space; H2CO3 »_space; CO2 + H2O.
What are the causes of metabolic alkalosis? (3)
- Generation of bicarbonate by gastric mucosa
- Renal generation of HCO3- in hypokalaemia
- Administration of bicarbonate
What are the main consequences of metabolic alkalosis? (3)
- K+»_space; cells and urine
- PO4»_space; cells
- Respiratory suppression
What are the main signs / symptoms of metabolic alkalosis?
- Vomiting/diarrhoea
- Renal failure
- Drug use
- GI surgery
What causes respiratory alkalosis?
Increased CO2 excretion due to hyperventilation.
-CO2 excretion > CO2 production
How does respiratory alkalosis typically present?
- Paresthesia
- Chest pain
- Dyspnoea
- Dizziness
What electrolyte imbalances does respiratory alkalosis cause?
- Decreased H+
- Increased pO2
- Decreased pCO2
What are the main causes of respiratory acidosis? (3)
CO2 retention due to:
- inadequate ventilation
- parenchymal lung disease
- inadequate perfusion
How does respiratory acidosis typically present?
- Anxiety
- Confusion
- Dyspnoea
- Disturbed sleep
What electrolyte imbalances does respiratory acidosis cause? (3)
- Increased H+
- Decreased pO2
- Increased pCO2
What are the main causes of metabolic acidosis? (4)
- Increased H+ formation
- Acid ingestion
- Reduced renal H+ excretion
- Loss of bicarbonate
What are the main causes of increased H+ formation? (4)
- Ketoacidosis (alcoholic/diabetes)
- Lactic acidosis
- Poisoning
- Inherited organic acidoses
What are the main symptoms of metabolic acidosis?
- Collapse
- Hyperventilation
- Tiredness
- Weight loss
- Jaundice
What is diabetic keto-acidosis?
Lack of insulin»_space;
- hyperglycaemia
- hyperketonaemia
- increased FFA
which all»_space; ACIDOSIS.
What are the 2 types of lactic acidosis?
- Type A - shock (decreased O2)
- Type B - metabolic / toxic causes
Does high lactate always lead to lactic acidosis?
No, not in alkalosis.
|»_space; increased glycolysis and vasoconstriction
What causes reduced H+ excretion? (2)
- Renal tubular acidosis
- Generalised renal failure
How does renal failure cause reduced H+ excretion?
REDUCED VOLUME OF NEPHRONS;
- increased HCO3- loss
- reduced NH4+ secretion
- NH4+ is needed by liver for urea and H+ synthesis
What else is H+ derived from apart from NH4+?
Glutamine.
-only a very small fraction
How do can chronic alcoholism lead to acidosis?
NAD+ depletion >> thiamine deficiency >> enhanced glycolysis >> keto-acids >> vomiting
