Carbon Dioxide Transport + Role In pH Balance Flashcards
Why is a very low blood pH a cause of coma?
- phosphofructokinase is pH dependent > activity decreases with decreasing pH
- glucose utilisation in brain cells is impaired
What are clinical consequences of decreases blood pH?
Drowsiness
Stupor - near unconsciousness
Coma
What is the blood pH range?
7.35-7.45
How can CO2 form H+ and bicarbonate ions?i
CO2 + H2O <-> H2CO3 <-> H+ + HCO3-
- reacts with water to form carbonic acid
- carbonic acid dissociates into H+ and HCO3-
Ratio between CO2 and HCO3- in order to maintain normal body pH
CO2 : HCO3-
1 : 20
Why must we have methods of transport of CO2 in blood?
- To prevent drop in pH
- 1:20 ratio of CO2:HCO3 needed to maintain normal body pH
- 1 CO2 only produces 1 HCO3-
- blood pH will become more acidic i due to excess H+ ions without alternate transport
What are the methods of transport of CO2 in blood?
Carb amino compounds
As bicarbonate
Dissolved in plasma
How do we form carbamino compounds?
CO2 binds to haemoglobin (to amine groups)
Function of carbamino compounds
- stabilising pH
- stabilises T state of haemoglobin > promotes release of O2 into respiring tissues
What happens to carbamino compounds at the lungs?
- CO2 given up by haemoglobin
- Hb becomes O2 rich
- CO2 expired
Haldane effect
How much CO2 is transported as bicarbonate ions in RBCs?
60%
What enzyme converts CO2 to bicarbonate ions in RBCs?
Carbonic anhydrase
How is excess HCO3- transported back into the blood?
Via chloride-bicarbonate exchanger
Act as a buffer to H+ in blood plasma.
What is haemoglobin role in H+ buffering?
- less O2 bound to Hb > T state > more H+ ions bind
- more O2 bound to Hb > R state > less H+ ions bind
How does bicarbonate buffer extra acid?
H+ + HCO3- > CO2 + H2O
- CO2 levels increase > removed by breathing
- More HCO3 must be produced to replenish buffers
What is the role of the kidneys and the lungs in blood pH?
- lungs: how much CO2 is present > change rate/depth of breathing | faster response
- kidneys: how much HCO3- is present | slower response
What is HCO3- conc. controlled by?
Kidneys
How much CO2 is transported in plasma?
10%
How much CO2 is transported as carbamino compounds?
30%
Relationship between pCO2 and pH
inversely proportional
if pCO2 falls > pH rises
if pCO2rises > pH falls
Why is the reaction of CO2 to carbonate ions faster in RCBs than plasma?
Carbonic anhydrase in RBCs
Enzyme increases speed of reaction
How is the majority of CO2 transported?
As bicarbonate ions
Define respiratory acidosis
Failure of ventilation leading to accumulation of CO2 causing a decrease in pH
Define respiratory alkalosis
Hyperventilation causes low levels of CO2 resulting in an increase in pH
Steps in interpreting arterial blood gas
- look at pH: normal/acidosis/alkalosis
- look at pCO2: respiratory
- look at HCO3-: metabolic
- look at HCO3- again: check for compensation
- look at pCO2 again: check for compensation
What does the pCO2 result in a ABG tell you?
Where it’s respiratory or not
High pCO2 > acidifying effect
Low pCO2 > alkalising effect
What does the bicarbonate result tell you in an ABG?
Where its metabolic or no t
Low HCO3- > acidosis
High HCO3- alkalosis
Difference between hypoxia + hypoxemia
- hypoxaemia: decreased pO2 in blood
- hypoxia: decreased level of O2 in tissues
