Oxygen Transport in Blood

I. Oxygen-Hemoglobin Dissociation Curve (ODC)

• Definition: Plots % hemoglobin saturation with O₂ vs. partial pressure of O₂ (PO₂).
• Shape: Sigmoidal (S-shaped) due to cooperative binding.
  • Steep Portion: Efficient O₂ unloading at tissue PO₂.
  • Flat Portion: Efficient O₂ loading at lung PO₂.

Shifts of the ODC

• Right Shift (Decreased O₂ Affinity): Hemoglobin releases O₂ more readily.
  • Factors (CADET, Right!):
    • CO₂ (Increased PCO₂)
    • Acidity (Increased H⁺ / Decreased pH)
    • DPG (Increased 2,3-Bisphosphoglycerate)
    • Exercise (Increased metabolism)
    • Temperature (Increased)

Shifts of the ODC (Continued)

• Left Shift (Increased O₂ Affinity): Hemoglobin holds onto O₂ more tightly.
  • Factors:
    • Decreased PCO₂
    • Decreased H⁺ / Increased pH
    • Decreased 2,3-BPG
    • Decreased Temperature
    • Fetal Hemoglobin (HbF)
    • Carbon Monoxide (CO) Poisoning

II. Key Physiological Effects

• A. The Bohr Effect: Increased CO₂ and H⁺ (decreased pH) decrease Hb's O₂ affinity, shifting ODC right. (O₂ unloading in tissues).
• B. The Haldane Effect: Deoxygenated Hb has increased capacity to carry CO₂ and H⁺. (CO₂ loading in tissues, unloading in lungs).
• C. Effect of 2,3-Bisphosphoglycerate (2,3-BPG): Binds to Hb, reducing O₂ affinity (right shift), especially in hypoxia.
• D. Effect of Temperature: Increased temperature decreases Hb's O₂ affinity (right shift).

III. Carbon Dioxide Transport

• Three Forms:
  1. Dissolved in Plasma (7-10%)
  2. Bound to Hemoglobin (Carbaminohemoglobin) (20-30%)
  3. As Bicarbonate Ions (HCO₃⁻) (60-70%) - Most significant.

IV. The Chloride Shift (Hamburger Effect)

• In Tissues (CO₂ Loading):
  1. CO₂ enters RBC, forms H₂CO₃ (by Carbonic Anhydrase).
  2. H₂CO₃ dissociates to H⁺ (buffered by Hb) and HCO₃⁻.
  3. HCO₃⁻ moves out to plasma; Cl⁻ moves into RBC to maintain electrical neutrality.

The Chloride Shift (Continued)

• In Lungs (CO₂ Unloading / Reverse Chloride Shift):
  1. O₂ binds to Hb, releasing H⁺ (Haldane effect).
  2. H⁺ combines with HCO₃⁻ (from plasma) to form H₂CO₃.
  3. H₂CO₃ converts to CO₂ and H₂O (by Carbonic Anhydrase).
  4. CO₂ diffuses out of RBC to alveoli; Cl⁻ moves out of RBC to plasma.

V. Interplay and Integration

• All these effects (ODC shifts, Bohr, Haldane, Chloride Shift) work together.
• In Tissues: Promote O₂ unloading and CO₂ loading.
• In Lungs: Promote O₂ loading and CO₂ unloading.
• Ensures efficient gas exchange based on metabolic needs.