Flashcards in Acid Base Balance And Osmolarity Deck (49)
What is the reference range for plasma H+ ions?
35.5 - 44.5 nmol/L
How does alkalosis affect calcium?
Lowers free Ca2+
Causes Ca2+ ions to come out of solution
Increased neuronal excitability
Paraesthesia and tetany
How does acidosis affect proteins?
Decreased pH due to increased H+ ions
Affects muscle contractility, glycolysis and hepatic function
About which pH do we consider acidosis severe and then life threatening?
Severe < 7.1
Life threatening < 7.0
What number is the constant pK in the Henderson-Hesselbach equation?
What is the normal physiological pH?
How would respiratory acidosis occur?
Leads to hypercapnia (increased CO2 in plasma)
This decreases plasma pH
How does respiratory alkalosis occur?
Hyperventilation causes hypocapnia in the plasma
Fall in CO2 causes increase in pH
How is respiratory acidosis compensated for?
Kidneys increase the level of bicarbonate
How is respiratory alkalosis compensated for?
Kidneys decrease the concentration of bicarbonate
What is metabolic acidosis?
A fall in pH due to a fall in conc of bicarbonate
Can be compensated for by increased ventilation
What is metabolic alkalosis?
A rise in plasma bicarbonate which can only be partially compensated by decreasing ventilation
What is a common cause of metabolic alkalosis?
How do the kidneys increase bicarbonate levels?
Excrete less bicarbonate in the urine
Make more bicarbonate
What do the kidneys use to make bicarbonate?
Kidneys have a high conc of CO2 due to their high metabolic rate - react this with water to form bicarbonate
Also can make bicarbonate from amino acids
(This means ammonium will be present in the urine)
Where does the majority of bicarbonate reabsorption take place?
Describe the mechanism for reabsorption of bicarbonate
Na/K/ATPase on basolateral membrane creates the Na+ gradient
Na+ enters cell in exchange for H+ (NHE on apical membrane)
H+ reacts with the bicarbonate to form CO2 and water which can diffuse into the cell
In the cell it is reconverted into HCO3- and H+
HCO3- passes out of the cell via the Na-HCO3 symporter on the basolateral membrane
Which amino acid is used to produce bicarbonate?
What is the minimum urine pH?
Should there be HCO3- in the urine normally?
How is acid in the urine excreted?
Buffered by phosphate (titratable)
Reacted with NH3 = NH4+
What is the normal H+ excretion per day?
50 - 100 mmol/day
Why do we excrete acid in the urine?
To maintain the concentration of bicarbonate in the plasma
How does a decreased pH affect the kidneys in order to correct itself??
Enhances activity of Na+/H+ exchanger
Enhances ammonium production in PCT
Enhances activity of H+/ATPase in DCT
Increased capacity to export HCO3- into ECF
What is the anion gap?
Difference between the cations (Na+/K+) and the anions (HCO3-/Cl-)
(Normal = 10 - 15 mmol/L as there are unaccounted anions)
Why does the anion gap increase?
Anions from (paired to) metabolic acids replace HCO3-
(Other than Cl-)
Do all forms of metabolic acidosis create an anion gap?
How do we treat metabolic alkalosis?
Give them an infusion of bicarbonate
Causes a rapid excretion of bicarbonate so their levels will reduce
Why is there a problem if there is an alkalosis and a volume depletion?
Capacity to lose bicarbonate is reduced because of high rate of Na+ recovery
HCO3- will be reabsorbed with the Na+