Transport of carbon dioxide Flashcards
What is the typical carbon dioxide content in arterial blood?
48ml/dl
What are the forms in which carbon dioxide is carried in the blood?
Free in physical solution (3 ml/dl)
In chemical combination (45 ml/dl)
* Carbamino compound (3 ml/dl)
* Bicarbonate (42 ml/dl)
Describe the composition of the carbamino compounds carrying of carbon dioxide
In RBCs: Carb-Hb (CO2 + Hb)
In plasma: Carbamino protein (CO2 + plasma)
Describe the composition of bicarbonate compounds carrying of carbon dioxide
In RBCs: KHCO3
In plasma: NaHCO3
What is tidal CO2?
Level of carbon dioxide released at the end of an exhaled breath
What is the typical value of tidal CO2?
Under normal resting conditions = 4ml CO2/100ml blood
What is the buffering of tidal CO2?
Acid-base homeostatic mechanism involving the balance of carbonic acid (H2CO3), bicarbonate ion (HCO−3), and carbon dioxide (CO2) in order to maintain pH in the blood and duodenum, among other tissues, to support proper metabolic function
How much of each compound is maintained in the buffering of tidal CO2?
Technique 1: 0.4ml (10% of tidal CO2): Dissolve in physical solution → decrease PH from 7.4 to 7.34
Technique 2: 1ml (25% of tidal CO2): Change to carbamino compound. Oxy Hb + CO2 = reduced Hb
Technique 3: 2.6ml (65% of tidal CO2): Buffered by Hb with production of HCO3- (Cl- shift phenomenon)
Technique 3: Describe the Cl- shift phenomenon at the tissue level
CO2 enters RBC
CO2 hydrated to H2CO3 by carbonic anhydrase
H2CO3 is in equilibrium with H+ and its conjugate base, HCO3 −
H+ interacts with deoxyhemoglobin to form reduced Hb, whereas HCO3− can be transported outside of the cell via anion exchanger 1 (AE1 or Band 3) with Cl-
I.e. for each CO2 molecule that enters the red cell, there is an additional HCO3− or Cl− in the cell
Because of this chloride shift, the Cl− content of the red cells in venous blood is significantly greater than that in arterial blood.
Technique 3: Describe the Cl- shift phenomenon at the lung level
HCO3- passes from plasma to RBCs and Cl- moves out of the RBCs into the plasma
Carbonic acid dissociates into H2O and CO2
CO2 diffuses to the alveoli to go outside with expiration.
What is the CO2 dissociation curve?
Shows the relationship between the total CO2 content of blood and CO2 tension (PCO2)
↑ PCO2 = ↑ CO2 content
Value of PCO2 and CO2 content in the lungs and tissue
At the lung: PCO2 = 40mmHg → CO2 content = 48ml/dl
At the tissues: PCO2 = 46mmHg → CO2 content = 52ml/dl
Therefore, Tidal CO2 = 52-48 = 4ml/dl
What is the Haldane effect?
Oxygenation of blood in the lungs displaces carbon dioxide from hemoglobin, increasing the removal of carbon dioxide to the alveoli
Binding O2 with the Hb → displace (release) CO2 from the blood to the alveoli
Haldane effect but on a graph
At the tissues (point A):
PO2 = 40mmHg
PCO2 = 46mmHg → CO2 content = 52ml/dl
At the lung (point B):
PO2 = 100mmHg
PCO2 = 40mmHg → CO2 content = 48ml/dl
Without PO2 shift, CO2 content will reduce from 52 ml/dl to 50 ml/dl (only 2 ml of CO2 loss)
But on entering the lung, PO2 rise → shift of CO2 dissociation curve down → additional 2ml loss of CO2 to become 48ml/dl
What is the Bohr effect?
Increase CO2 and H+ → Shift of O2 dissociation curve to the right → Release of O2 to the body tissues
