O2/ C02 Transport

Oxygen Transport

  • Oxygen Loading

    • One oxygen molecule is picked up by each hemoglobin in the red blood cell.

    • This occurs in the alveoli where oxygen enters the blood.

    • Hemoglobin can carry up to four oxygen molecules, but initially starts with three after releasing one to the tissues.

    • Red blood cells, after being recharged with oxygen, travel back to the left side of the heart.

  • Oxygen Delivery

    • Hemoglobin releases one oxygen molecule to tissues.

    • The process repeats, with carbon dioxide transported back to the lungs.

Carbon Dioxide Transport

  • Introduction to Carbon Dioxide Transport

    • More complex than oxygen transport.

    • Carbon dioxide is transported in three primary ways.

  • 1. Dissolved in Plasma

    • Small amount of carbon dioxide enters the plasma directly.

    • Least common method of transport (about 10% of carbon dioxide).

  • 2. Binds to Hemoglobin (Carbamino Compounds)

    • Carbon dioxide enters the red blood cell and binds to the globin part of hemoglobin (not the iron part).

    • This compound is called carbaminohemoglobin.

    • About 20-30% of carbon dioxide is transported this way.

  • 3. Converted to Bicarbonate (Most Complex Process)

    • Inside the red blood cell, carbon dioxide combines with water to form carbonic acid (H2CO3), a process catalyzed by the enzyme carbonic anhydrase.

    • Carbonic acid is unstable and dissociates into hydrogen ions (H+) and bicarbonate ions (HCO3-).

    • The release of hydrogen ions can create a strong acidic environment.

    • Hydrogen ions bind with hemoglobin to buffer the pH.

    • Bicarbonate ions are transported out of the cell through a chloride shift, where chloride ions (Cl-) enter the cell to maintain electrical neutrality.

    • This process accounts for approximately 70% of carbon dioxide transport.

Reversal at the Lungs

  • Exhalation of Carbon Dioxide

    • At the lungs, carbon dioxide must be reversed back to its gaseous form for exhalation.

    • 1. Dissolved Carbon Dioxide: Easily released from plasma to alveoli.

    • 2. Carbaminohemoglobin: Carbon dioxide dissociates from hemoglobin; hemoglobin remains, and carbon dioxide is freed to enter the alveoli.

    • 3. From Bicarbonate:

      • Bicarbonate ions are transported back into the red blood cell, chloride ions exit.

      • Bicarbonate combines with hydrogen ions to reform carbonic acid, which then breaks down into water and carbon dioxide.

      • Carbon dioxide is then released into the alveoli for exhalation.

Clinical Relevance

  • Understanding carbon dioxide transport is critical in clinical settings, especially for nursing students.

  • The interaction between carbon dioxide, water, and carbonic acid regulates blood pH, which affects various pathophysiological conditions (e.g., respiratory acidosis, alkalosis).

  • Future clinical applications include calculating bicarbonate and pH levels based on carbonic acid equilibrium, crucial for patient care.