Human

• Explain the essential features of the alveolar epithelium that makes it adapted as a surface for gas exchange

  • Flattened cells/1 cell thick - Short diffusion pathway
  • Folded - Large Surface Area
  • Permeable - Allows for diffusion of O2/CO2
  • Moist - Gasses can dissolve for diffusion
  • Good blood supply from large network of capillaries - Maintains concentration gradient
• Describe how gas exchange occurs in the lungs

  • Oxygen diffuses from alveolar air space into blood down the concentration gradient
  • Across alveolar epithelium then across capillary endothelium
• Explain the importance of ventilation

  • Brings in air containing higher conc of oxygen and removes air with lower conc of oxygen
  • Maintaining the concentration gradient
• Explain Inspiration (Breathing in)

  1. Diaphragm muscles contract - Flattens
  2. External intercostal muscles contract, internal intercostal muscle relax (Antagonistic) - Rib cage is pulled up and out
  3. Increasing volume and decreasing pressure in thoracic cavity
  4. Air moves into lungs from high pressure to low pressure down pressure gradient
• Explain Expiration (Breathing out)

  1. Diaphragm relaxes - Moves upwards and forms a dome shape
  2. External intercostal muscles relax, internal intercostal muscle may contract - ribcage moves down and in
  3. Decreasing volume and increasing pressure in thoracic cavity
  4. Air moves out of lungs from high pressure to low pressure down pressure gradient
• Suggest why expiration is normally passive at rest

  • Internal intercostal muscles do not normally need to contract
  • Expiration is aided by elastic recoil in alveoli
• Suggest how different lung diseases reduce the rate of gas exchange

  • Thickened alveolar tissue (E.g. fibrosis) - Increases diffusion pathway
  • Alveolar wall breakdown - Reduces surface area
  • Reduce lung elasticity - Lungs expand/recoil less - reduces concentration gradient of O2/CO2
• Suggest how different lung diseases affects ventilation

  1)Reduce lung elasticity (E.g. fibrosis - build up of scar tissue) - Lungs expand/recoil less

  • Reducing volume of air in each breath (Tidal Volume)
  • Reducing maximum volume of air breathed out in one breath (Forced vital capacity)

  2)Narrow airways/reduce air flow in & out of lungs (E.g. asthma - inflamed bronchi)

  • Reducing maximum volume of air breathed out in 1 second

  3)Reduced rate of gas exchange - increased ventilation rate to compensate for reduced oxygen in blood
• Suggest why people with lung disease experience fatigue?

  Cells receive less oxygen - rate of aerobic respiration reduced - less ATP made