Lecture Notes: Oxygen and Carbon Dioxide Exchange Between Lungs and Tissues

Key Concepts

• Oxygen and Carbon Dioxide Exchange
  • Lungs send oxygen to tissues, while tissues send carbon dioxide back to the lungs.
  • Oxygen transport occurs primarily via hemoglobin (oxyhemoglobin, HbO2).
  • Carbon dioxide returns to the lungs primarily via protonated hemoglobin and bicarbonate.

Oxygen Transport

• Dissolved Oxygen: A small amount is dissolved in blood.
• Oxyhemoglobin: The primary method of oxygen transport; oxygen binds to hemoglobin.

Carbon Dioxide Transport

• Dissolved CO2: Some CO2 dissolves directly in plasma.
• Protonated Hemoglobin: CO2 binds to hemoglobin and forms bicarbonate in plasma, aided by the enzyme carbonic anhydrase.
• Direct CO2 Binding: Hemoglobin can bind directly to CO2, forming protons.

Competition and Affinity

• Hemoglobin's ability to bind oxygen is affected by the presence of protons and CO2.
• Oxygen affects hemoglobin's affinity for CO2 and protons as well.
• These interactions are described by the Bohr and Haldane effects.

The Bohr Effect

• Definition: CO2 and protons decrease hemoglobin's affinity for oxygen.
• Illustration:
  • At higher CO2/proton levels (e.g., in muscle tissues), oxygen release is enhanced.
  • The oxygen delivery can be visualized by comparing differences in oxygen content between lungs and tissues.

The Haldane Effect

• Definition: Oxygen decreases hemoglobin's affinity for CO2 and protons.
• Illustration:
  • At higher oxygen levels (e.g., in lungs), CO2 release is enhanced.
  • CO2 content and delivery can be visualized by comparing differences in CO2 content between tissues and lungs.

Graphical Representation

• Bohr Effect Curve:
  • Shows relationship between partial pressure of oxygen and oxygen content.
  • Increased delivery through reduced hemoglobin affinity in high CO2 environments.
• Haldane Effect Curve:
  • Shows relationship between amount of CO2 and its content in blood.
  • Increased delivery through reduced affinity in high oxygen environments.

Conclusion

• Both effects are crucial in optimizing oxygen and CO2 transport between lungs and tissues.
• They provide mechanisms to adaptively manage oxygen and CO2 delivery based on the body's varying conditions.