Oxygen Molecule Pathway and Gas Exchange

Introduction

• Oxygen enters the body through the mouth or nose.
• Travels through the trachea to the lungs.
• Splits to the left lung (with cardiac notch) or right lung (no cardiac notch).

Focus on Alveoli

• Alveoli are the site of gas exchange in the lungs.
• Millions of alveoli facilitate the transfer of oxygen into the blood.

Oxygen Movement through the Alveolus

• Alveolus to Blood Vessel Pathway:
  • Starts in the gas phase in the alveolus.
  • Enters a thin fluid layer inside the alveolus.
  • Passes through epithelial cells (pancake-shaped).
  • Moves into the base membrane, providing structural support.
  • Transverses connective tissue and another base membrane.
  • Enters endothelial cells forming capillary walls.
  • Finally reaches the plasma and enters the red blood cells.

Oxygen Binding in Red Blood Cells

• Red blood cells contain hemoglobin.
• Hemoglobin binds up to four oxygen molecules.
• Oxygen is transported to the body as needed.

Visual Representation

• A conceptual rectangular cube is used to illustrate the oxygen's journey from alveolus (top) to red blood cells (bottom).
• Divided into gas and liquid phases to simplify understanding.

Relevant Equations

Alveolar Gas Equation

• Describes how much oxygen moves into the alveolus.
• Helps determine the partial pressure of oxygen (PO2) in the alveolus.

Fick's Law

• Calculates oxygen diffusion based on gradient, area, diffusion coefficient, and thickness.
• Formula: v = (gradient * area * diffusion coefficient) / thickness
• Important for determining oxygen delivery to red blood cells.

Factors Affecting Oxygen Diffusion

• FiO2 (Fraction of inspired oxygen): Higher in patients using supplemental oxygen.
• Altitude: Changes in altitude affect oxygen diffusion.
• Surface Area: Reduced working alveoli decrease effective gas exchange.
• Thickness: Increased fluid in layers can increase diffusion path.

Considerations

• P1 (Partial pressure in alveolus): Important to monitor changes.
• Area and Thickness: Critical factors affecting gas exchange.
• Diffusion Coefficient: Generally stable under constant conditions.
• P2 (Partial pressure in returning blood): Typically consistent barring increased body oxygen usage.

Conclusion

• Systematically assess variables (P1, area, thickness) when encountering abnormal oxygen diffusion.
• Understanding equations and oxygen pathway aids in diagnosing issues in gas exchange.