Oxygen and CO2 Transport

Overview

• Focus on how respiratory gases are carried throughout the body, primarily through hemoglobin.
• Oxygen transport is primarily via binding to hemoglobin in red blood cells.
• Carbon dioxide is transported in three ways: dissolved in plasma, bound to hemoglobin, and as bicarbonate.

Oxygen Transport

• Solubility Coefficient: Oxygen has a low solubility coefficient, meaning very little dissolves in plasma.
• Hemoglobin Function:
  • Contains iron atoms; 4 heme groups per molecule.
  • Each hemoglobin can bind 4 O2 molecules.
  • 98% of O2 is bound to hemoglobin (oxyhemoglobin), while the rest is dissolved in plasma.
  • Deoxyhemoglobin binds hydrogen ions when oxygen is not present.

Measuring Oxygen Levels

• Pulse Oximeter: Measures hemoglobin saturation (oxyhemoglobin vs. deoxyhemoglobin ratio).
• Saturation should exceed 95%; factors like methhemoglobin affect readings.

Carbon Dioxide Transport

• Three Methods:
  1. Dissolved in plasma (7%).
  2. Bound to globin portion of hemoglobin (23%), forming carbaminohemoglobin.
  3. As bicarbonate (70%), via the carbonic acid-bicarbonate reaction.
• Carbonic Anhydrase: Catalyzes reaction both ways, critical for CO2 transport and pH buffering.

Oxygen and CO2 Loading/Unloading

• Loading/Unloading Mechanism:
  • O2 loading in lungs and CO2 unloading are interdependent processes.
  • Conversely, O2 unloading in tissues is paired with CO2 loading.
• Chloride Shift: Balances ion exchange, maintaining neutrality.

Hemoglobin Saturation and Partial Pressure

• Oxygen-Hemoglobin Saturation Curve:
  • Non-linear, s-shaped curve.
  • Shows relationship between hemoglobin saturation and pO2.
  • Cooperative binding: Each O2 binding facilitates the next.
  • Large saturation change with small pO2 change at lower pressures.

Factors Affecting Hemoglobin's Oxygen Affinity

• Right Shift (in tissues):
  • Increased temperature, pCO2, and decreased pH (Bohr effect) decrease oxygen affinity.
  • Facilitates O2 unloading in tissues.
• Left Shift (in lungs):
  • Decreased temperature, pCO2, and increased pH enhance oxygen affinity.
  • Facilitates O2 binding in the lungs.

Altitude and Oxygen Saturation

• Higher altitudes decrease pO2, affecting hemoglobin's ability to load oxygen.
• Acclimatization involves increased red blood cell production.

Pathological Conditions

• High Altitude Pulmonary Edema (HAPE) and Cerebral Edema (HACE): Result from inadequate oxygen transport due to low atmospheric pressure.

Summary

• Understanding oxygen and CO2 transport is crucial in physiology.
• Hemoglobin plays a central role in gas transport, influenced by physiological conditions.