Overview
This lecture explains the transport mechanisms of carbon dioxide and oxygen in blood, focusing on the forms, chemical reactions, and physiological effects involved.
Carbon Dioxide Transport Forms
- Carbon dioxide is transported in blood as dissolved CO₂ (7%), carbaminohemoglobin (23%), and bicarbonate (70%).
- Dissolved CO₂ concentration is calculated using Henry's Law: partial pressure × solubility constant.
- CO₂ is more soluble in blood than O₂; 2.8 mL CO₂ vs 0.3 mL O₂ per 100 mL blood.
Binding and Chemical Reactions
- CO₂ binds to the N-terminus of hemoglobin's globin chain, while O₂ binds to the heme moiety.
- Carbonic anhydrase in red blood cells converts CO₂ to carbonic acid, which dissociates to H⁺ and bicarbonate (HCO₃⁻).
- Bicarbonate exits red blood cells in exchange for chloride ions via the chloride shift (band three protein).
- H⁺ is buffered by deoxyhemoglobin in red blood cells to maintain blood pH.
Bohr and Haldane Effects
- Bohr effect: Binding of CO₂ to hemoglobin decreases O₂ affinity, aiding oxygen release in tissues.
- Haldane effect: Binding of O₂ to hemoglobin decreases CO₂ affinity, promoting CO₂ release in alveoli.
- In tissues, high CO₂ facilitates O₂ unloading; in lungs, high O₂ facilitates CO₂ unloading.
Oxygen Transport Summary
- Oxygen is transported as 2% dissolved in plasma and 98% bound to hemoglobin.
- Oxyhemoglobin travels via systemic circulation to tissues, where O₂ diffuses into tissue due to partial pressure differences.
- High tissue CO₂ promotes O₂ release from hemoglobin via Bohr effect.
Summary of Exchange in Lungs and Tissues
- In tissues: CO₂ produced, O₂ released from hemoglobin, CO₂ carried away as dissolved, carbamino, and bicarbonate forms.
- In lungs: O₂ binds to hemoglobin, CO₂ is released from hemoglobin and as bicarbonate (reconverted to CO₂ and exhaled).
Key Terms & Definitions
- Carbaminohemoglobin — Hemoglobin bound to carbon dioxide at the globin's N-terminus.
- Bicarbonate (HCO₃⁻) — The primary form (70%) in which CO₂ is transported in blood.
- Bohr effect — A decrease in hemoglobin's O₂ affinity caused by increased CO₂ or H⁺.
- Haldane effect — The decreased affinity of hemoglobin for CO₂ when O₂ is bound.
- Chloride shift — Exchange of chloride and bicarbonate ions across red cell membranes to maintain charge balance.
- Henry’s Law — States that gas concentration dissolved in liquid is proportional to its partial pressure and solubility.
Action Items / Next Steps
- Review mechanisms of gas transport and related effects.
- Study relevant diagrams showing O₂ and CO₂ transport pathways.
- Prepare for questions on differences between Bohr and Haldane effects.