Gas exchange in Humans

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  • Human Respiratory System
    • Epiglottis
      • Covers the opening to airways when food is being swallowed
    • Trachea
      • Strengthened by rings of cartilage to keep the airway open
    • Rib and Intercostal Muscle
      • Alter the size of the thoracic cavity to change volume/pressure
    • Bronchioles
      • Small passageway to alveoli
    • Pleural Membranes
      • Reduce friction
    • Diaphragm
      • Alters size of thoracic cavity to change volume/pressure
    • Bronchus
      • Carry air to and from each lung
    • Alveoli
      • Respiratory gas exchange surface
    • The respiratory system has two functions;
      • Ventilation
        • The purpose of ventilation is to move gases over the gas exchange surfaces to maintain a concentration gradient between blood in the capillaries and air in the alveoli
          • Mammals ventilate their lungs by negative pressure breathing, forcing air down into the lungs
            • In order for air to enter the lungs, the pressure inside must be lower than the atmospheric pressure outside
      • Gaseous Exchange
        • Gas exchange takes place in the alveoli
      • Features and adaptations;
        • Large surface area
          • Millions of alveoli
          • The extensive capillary network surrounding each alveolus
        • Moist Surface
          • Tissue fluid lining the alveolus allows gases to dissolve and diffuse across
        • Short diffusion pathway
          • The alveolar wall is a single layer of flattened epithelial cels
          • The capillary wall is a single layer of flattened endothelial cells
        • Maintenance of a steep concentration gradient
          • Ventilation ensures the O2 concentration in the alveolus is high
          • A dense capillary network and blood flow ensure that the oxygen concentration entering the alveolar capillaries is low
    • Advantages of internal lungs;
      • Infolding reduces heat loss
      • Infolding reduces water loss
      • Protected by ribcage

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