Acid Base Balance Flashcards
What is alkalaemia?
Plasma pH >7.45
What is acidaemia?
Plasma pH <7.35
What is the effect of alkalaemia?
Lowers free calcium - Ca2+ ions come out of solution
Increases neuronal excitability - leads to paraesthesia + tetany
What is the effect of acidaemia?
Increases plasma K+ concentration - effects excitability of muscle
Denatures proteins - effects muscle contractility, glycolysis + hepatic function
How is pH regulated?
CO2/HCO3- buffer system
CO2 + H2O H+ + HCO3-
Direction dependent on concentrations of reactants/products
How is pCO2 determined?
Ventilation - controlled by chemo receptors
How is [HCO3-] determined?
Controlled by the kidneys - variable recovery of HCO3- and secretion of H+
How does the kidney control [HCO3-]?
Recovery
Creation
How does the kidney recover HCO3-?
HCO3- filtered at glomerulus
Mostly recovered in PCT by a sodium cotransporter
How is HCO3- created in the kidney?
Glutamine -> α-ketoglutarate
Produces HCO3- + NH4+
HCO3- enters ECF
NH4+ enters lumen - excreted in urine
How does the kidney control H+?
Secrete H+ that is produced from CO2 reacting with water
H+ is actively secreted
H+ buffered by ammonia and phosphate
How is acid excreted?
In the urine
- H+
- buffered by phosphate
- reacted with ammonia to form ammonium
How much acid is secreted per day?
50-100 mmol H+ per day
What is the effect of acidosis on potassium?
Acidosis -> hyperkalaemia
- potassium ions move out of cells
- decreased potassium excretion in nephron
What is the effect of alkalosis on potassium?
Alkalosis -> hypokalaemia
- potassium ions move into cells
- increased secretion of potassium in nephron
What is the effect of hyperkalaemia on acid base balance?
Makes intracellular pH of tubular cells more alkaline
H+ ions move out of cells
This favours HCO3- secretion
METABOLIC ACIDOSIS
What is the effect of hypokalaemia on acid base balance?
Makes intracellular pH of tubular cells more acidic
H+ ions move into cells
This favours H+ secretion and HCO3- recovery
METABOLIC ALKALOSIS
How does hypoventilation effect acid base balance?
Hypoventilation -> hypercapnia
Hypercapnia -> fall in plasma pH
RESPIRATORY ACIDOSIS
How does hyperventilation effect acid base balance?
Hyperventilation -> hypocapnia
Hypocapnia -> rise in plasma pH
RESPIRATORY ALKALOSIS
What is compensation?
Changes in breathing rate to compensate for changes in [HCO3-]
OR
Changes in [HCO3-] to compensate for respiratory acidosis/alkalosis
What is the anion gap?
Difference between measured cations and anions
How do you calculate the anion gap?
([Na+]+[K+]) - ([Cl-]+[HCO3-])
What causes the anion gap to be increased?
HCO3- replaced by other anions - typically of metabolic acids
What happens to the anion gap in renal causes of acidosis?
Unchanged
Kidney not making enough HCO3- so its replaced by Cl-
