S4) Carbon Dioxide in the Blood Flashcards
Describe 3 chemical properties of carbon dioxide in the blood
- CO2 is more soluble than oxygen
- CO2 reacts chemically with water
- CO2 also reacts with Hb (different site from O2)
Compare and contrast the content of O2 and CO2 in arterial blood
- Total content CO2 in arterial blood ≈ 21 mmol.l-1
- Total content O2 in arterial blood ≈ 8.9 mmol.l-1
What is the normal range of arterial blood pH?
pH 7.35 – pH 7.45
What is the most important substance in controlling blood pH?
CO2
What is the solubility factor for CO2 at 37oC?
0.23
How does one calculate the [CO2]dissolved in blood?
[CO2]dissolved = solubility factor x pCO2
What is the role of dissolved CO2 in plasma and in red blood cells?
- Not a waste product
- Reacts with water to act as a buffer
What is the result of dissolved carbon dioxide reacting with water?
- Dissolved CO2 reacts with water to form carbonic acid
- Carbonic acid very quickly dissociates to hydrogen ions and hydrogen carbonate ions
![](https://s3.amazonaws.com/brainscape-prod/system/cm/403/702/216/a_image_thumb.png?1508417140)
pH of blood plasma depends on how much CO2 reacts to form H+.
What determines this?
- [CO2]dissolved (pushes reaction to right)
- [HCO3- ] (pushes reaction to left)
![](https://s3.amazonaws.com/brainscape-prod/system/cm/403/702/217/a_image_thumb.png?1508417325)
Explain the relationship between the plasma pH and pCO2 of the alveoli
[CO2]dissolved depends directly on pCO2:
- If pCO2 rises = plasma pH falls
- If pCO2 falls = plasma pH rises
Using the Hendersson-Hasselbach equation, what is the formula to calculate pH from pCO2 and [HCO3-] ?
![](https://s3.amazonaws.com/brainscape-prod/system/cm/403/702/220/a_image_thumb.png?1508425739)
How does one calculate the pH of blood plasma using the Hendersson-Hasselbach equation?
- pK is a constant (6.1 at 37oC)
- 20x more HCO3- than dissolved CO2 (log20 = 1.3)
pH = 6.1 + 1.3 = 7.4
![](https://s3.amazonaws.com/brainscape-prod/system/cm/403/702/222/a_image_thumb.png?1508425924)
Which values determine the pH of arterial blood?
- Ratio of [HCO3-] and pCO2 determine pH
- pCO2 determined by alveolar pCO2
- Alveolar pCO2 is determined by rate of ventilation
How is the plasma concentration of hydrogen carbonate established
Hydrogen carbonate production in red blood cells:
– C02 can recat with water inside RBC
- H+ ions bind to Hb(-) inside RBCs
- Chloride-bicarbonate exchanger transports HCO3- out of RBCs in exchange for Cland creates a plasma concentration of 25mmol.l-1 HCO3-
![](https://s3.amazonaws.com/brainscape-prod/system/cm/403/702/226/a_image_thumb.png?1508417866)
Which enzyme catalyses the production of hydrogen carbonate in red blood cells?
Carbonic anhydrase
this is a rapid reaction unlike in plasma as there is a high conc of it
C02 + H20 → H + Hco3