Transport of Carbon Dioxide in the Blood
Misconceptions on CO2 Transport
- Common misconception: CO2 transported like oxygen, by binding to hemoglobin.
- Actual process: More complex than direct binding to hemoglobin.
CO2 Diffusion and Initial Transport
- CO2 produced by body cells.
- Diffusion occurs from high CO2 concentration in cells to lower concentration in blood.
- CO2 initially enters the blood plasma but only 5% dissolves due to non-polar nature.
CO2 in Red Blood Cells
- 95% of CO2 enters red blood cells.
- 10% binds to hemoglobin, forming carbaminohemoglobin.
- CO2 binds to terminal amine groups of hemoglobin, not the heme group.
Conversion to Carbonic Acid
- Remaining 85% of CO2 binds with water.
- Catalyzed by Carbonic Anhydrase to form carbonic acid (H2CO3).
- Carbonic acid dissociates to hydrogen ions (H+) and hydrogen carbonate ions (HCO3-).
Role of Hydrogen Ions
- H+ binds to hemoglobin forming hemoglobinic acid.
- Prevents acidosis by buffering excess H+.
- Weak acid formation stabilizes blood pH around 7.35.
- Promotes oxygen release due to Bohr effect.
The Bohr Effect
- Increased CO2 leads to more carbonic acid and H+.
- H+ binding promotes O2 release from hemoglobin.
- Allows oxygen to diffuse into body cells.
Chloride Shift
- Maintains ionic balance in red blood cells.
- HCO3- diffuses out; Cl- ions move in to balance charge.
Importance of Hemoglobinic Acid
- Ensures stable blood pH by binding excess H+.
- Facilitates oxygen release in tissues needing respiration.
Summary
- Three main methods of CO2 transport:
- Dissolved in plasma.
- As carbaminohemoglobin (10%).
- As HCO3- ions in plasma (85%).
Potential Exam Questions
- Describe the three methods of CO2 transport in blood.
- Explain the significance of hemoglobin binding to H+.
- Why must the chloride shift occur?
- Effects of increased CO2 on blood pH.
This summary provides a concise understanding of how carbon dioxide is transported in the blood, highlighting key mechanisms and possible examination queries.