USMLE

Gas Exchange in Tissues

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Respiratory
  1. Respiratory Overview
  2. Airway Anatomy
  3. Alveoli
  4. Breathing Mechanics
  5. Gas Exchange in Tissues
  6. Nervous Control of Breathing
  7. Respiratory Defense Systems
  • Gas Exchange in Muscle/Tissue
    • Oxygen is exchanged for carbon dioxide between body tissues and systemic capillaries
      • Gases diffuse down their concentration gradients 
        • High concentration → low concentration
      • Muscle cells: Low pO2, high CO2
        • O2 diffuses from systemic capillaries to muscle cells
        • CO2 diffuses from muscle cells to systemic capillaries
    • Optimization feature:
      • RBCs move through capillaries single-file
        • More RBC surface area is exposed, increasing efficiency of gas exchange
    • Amount of gas dissolved in blood is determined by Henry’s Law (low yield)
      • C = P x solubility
        • C = concentration of dissolved gas
        • P = partial pressure of gas in equilibrium with the liquid
        • As partial pressure of a gas increases, concentration of gas dissolved in solution also increases
      • Application:
        • As O2 diffuses into capillaries from alveoli, pO2 of blood rises until it reaches the high pO2 in alveoli
        • This process facilitates dissolution of O2 in blood
        • Solubility of O2 in blood is not high enough for sufficient O2 to be dissolved for transport to body’s cells, so majority of O2 in blood is transported by Hb