Oxygen-Hemoglobin Dissociation Curve

Overview

• Focuses on understanding the oxygen-hemoglobin dissociation or saturation curve.
• Discusses the properties of red blood cells and hemoglobin.
• Explains factors affecting the dissociation curve.

Red Blood Cells (RBC) Basics

• Structure: Biconcave disc, no nucleus.
• Energy Source: Glycolysis (converts glucose to pyruvate, produces ATP).
• Protein Content: Up to 270 million hemoglobin molecules per RBC.

Hemoglobin Structure

• Subunits: 4 (α1, α2, β1, β2).
• Oxygen Binding: Cooperative binding (allosteric binding) increases affinity with each successive oxygen molecule.

Oxygen-Hemoglobin Dissociation Curve

• Axes: Y-axis = Percent saturation of hemoglobin, X-axis = Partial pressure of oxygen (mm Hg).
• Key Points:
  • Lungs (105 mm Hg, 98.5% saturation).
  • Tissue level (40 mm Hg, 75% saturation).
• Oxygen Unloading: At tissue level, roughly 23% of oxygen is released from hemoglobin.

Factors Affecting the Curve

• Rightward Shift (CADET mnemonic):
  • Carbon Dioxide (CO₂)
  • Acidity
  • 2-3 Bisphosphoglycerate (BPG)
  • Exercise
  • Temperature
• Impact of Rightward Shift:
  • Decrease in saturation at tissue level (50% saturation at 40 mm Hg).
  • Increased oxygen delivery to tissues (48% of available oxygen).

Leftward Shift

• Conditions:
  • Decrease in CO₂, acidity, temperature, and 2-3 BPG.
  • Associated with sedentary, cold conditions.
• Impact of Leftward Shift:
  • Higher saturation at tissue level (85% saturation at 40 mm Hg).
  • Decreased oxygen delivery (13% of available oxygen).

Fetal Hemoglobin

• Characteristics: Higher affinity for oxygen, shifts curve to the left.
• Importance: Allows efficient transfer of oxygen from mother to fetus through the placenta.

Conclusion

• The oxygen-hemoglobin dissociation curve is dynamic and adapts to physiological conditions.
• Understanding the curve is crucial for grasping how oxygen is delivered to tissues under different conditions.