(11) gas exchange in humans

• features of gas exchange surfaces:

  • large surface area, more alveoli, more diffusion
  • thin surface, 1 cell thick, shorter diffusion distance
  • good blood supply, maintain concentration gradient
  • good ventilation, maintain concentration gradient
• cartilage in trachea: supports and strengthens trachea preventing it from collapse
• concentration of oxygen in the blood is lower, inhaled oxygen diffuses in (through walls of alveoli and enters bloodstream)
• concentration of carbon dioxide in the blood surrounding alveoli is higher than inhaled carbon dioxide, it diffuses out
• body’s warmth causes water from alveoli surface to evaporate into expired air
• inspire:

  • oxygen: 21%
  • carbon dioxide: 0.04%
  • water vapour: variable
• expire:

  • oxygen: 16% 
  • carbon dioxide: 4%
  • water vapour: saturated
• inspire: 

  • external intercostal: contract
  • internal intercostal: relax
  • ribcage: upwards, outwards
  • volume in thorax: increase
  • pressure in thorax: decrease
  • atmosphere pressure: more than thorax
  • air movement: into lungs
• expire

  • external intercostal: relax
  • internal intercostal: contract
  • ribcage: downwards, inwards
  • volume in thorax: decrease
  • pressure in thorax: increase
  • atmosphere pressure: less than thorax
  • air movement: out of longs
• exercise increase rate and depth of breathing:

  • an increased carbon dioxide concentration in blood
  • detected by brain
  • leading to increased rate and greater depth of breathing
• goblet cells: produce mucus

  mucus: traps dust and pathogens

  ciliated cells: sweeps mucus