Regulation of plasma pH Flashcards
pH =
-log10[H+]
Normal blood pH =
7.4 +/- 0.4
Normal blood [H+] =
~40nM (35-45nM/L)
Physiological changes due to pH acidosis
Renal ammoniagenesis
Pulmonary vasoconstriction
Systemic vasodilation
Hyperventilation
Outside of what pH range do pathological effects associated with acidosis/alkalosis occur??
7.35-7.45
Pathological changes due to pH acidosis
Hyperkalemia (K+ leaves cells) Reduced cardiac contractility Bone reabsorption (H+ replaces Ca2+) Cerebral palsy in newborns Death
Physiological changes due to pH alkalosis
Hypoventilation
Systemic vasoconstriction
Pulmonary vasodilation
Renal bicarbonate secretion
Pathological changes due to pH alkalosis
Tetany from low Ca2+ (calcium binding to albumin is altered at high pH) Fainting from low cerebral blood flow Hypokalemia Cardiac dysrhythmia Haemolysis Death
What is the SID?
Difference between the sum of all positive ions and the sum of all strong negative ions
What is the SID value?
~40mM
What controls SID?
The kidneys
What are the two basic ways to change the H+ concentration in the blood?
Metabolic change
Respiratory change
If you plot [H+] against pCO2 what does the graph look like?
As pCO2 increases, [H+] increases
If you plot [H+] against pCO2, how does changing the SID change the graph?
Lower SID, graph moves steeper, higher SID graph less steep (lower SID means greater [H+] as the sum of SID and H+ = sum of negative ions)
If you plot [H+] against pCO2, how does changing the protein conc change the graph?
Lower protein concentration graph becomes less steep, raise protein concentration, steeper graph (H+ + SID = negative ions incl protein-)
How do you view a metabolic pH change on the H+/pCO2 graph?
Move up and down graphs, stay at constant pCO2 (changing the SID or protein conc i.e metabolic changes)
How do you view a respiratory pH change on the H+/pCO2 graph?
Slide up and down a single line at set SID/protein level, as pCO2 changes (respiratory) H+ changes
What is the davenport diagram?
Plot [HCO3-] against pH (horizontal) then lines on constant pCO2 create bands (isobars) on the graph.
How are metabolic changes shown on a davenport diagram?
are represented through a movement up and down the pCO2 lines (as pCO2 remains constant, but pH rises or falls)
How are respiratory changes represented on a davenport diagram?
are represented through movements along the respiratory line that pass through different pCO2 values
What can change the slope of the davenport line?
Presence of protein makes the line more extreme, (i.e Hb concentration)
Causes of metabolic acidosis
Exercise: rapid production of lactic acid (pK=~4) (especially in anaerobic exercise)
Diabetic ketoacidosis: insulin deficiency leads to production of acetoacetic acid and B-hydroxybutyric acid, ketone bodes have pK=~4, act as strong negative ions
Diarrhoea: loss of sodium and bicarbonate - lower SID
Renal failure: changing chloride concertation in blood, retain Cl- and lower SID
Acetazolamide: CA inhibitor, reduces reabsorption of HCO3-, retains more Cl-, lower SID
Causes of metabolic alkalosis
Antacid excess: ingestion of alkaline metabolic substance
Vomiting: HCl loss from stomach
Aldosteronism: excessive aldosterone leads to extreme sodium retention, raises SID
Diuretic therapy: losses of K+ and H+, raise SID
Causes of respiratory alkalosis (hyperventilation)
Anxiety: increased drive to breathe
Hypoxia: as at high altitude
Voluntary overbreathing
