Lung and gas exchange

• Lungs


  Function: Get the oxygen that we need from the air all around us into our bloodstream where it can be transported to the rest of the body
• Air flow through the lungs

  1. Mouth/nose

  2. Trachea

  3. Bronchi

  4. Bronchioles

  5. Alveoli
• Alveoli


  • Small sacks arranged like bunches of grapes
  • Site of gas exchange
• Alveolus


  Single alveolus
• Alveolus


  • Made up of one layer of very thin cells
  • Short diffusion pathway
  • Large surface area
  • Moist alveolar walls
• Oxygen in alveoli


  Diffuses into blood
• Carbon dioxide in blood

  Diffuses into alveoli and is breathed out
• Carbon dioxide is dissolved in blood plasma, not carried by red blood cells like oxygen
• Gas exchange happens continually with a constant supply of deoxygenated blood entering capillaries and oxygenated blood leaving
• Breathing rate


  Number of breaths taken per minute
• Calculating breathing rate


  Divide number of breaths by time in minutes
• Lungs


  • Air passes into the lungs through a tube called the trachea
  • Trachea contains rings of cartilage to prevent it from collapsing when we inhale
  • Trachea splits into two smaller tubes called bronchioles
  • Bronchioles subdivide into many smaller tubes
  • Bronchioles end in tiny air sacs called alveoli
  • Lungs contain a huge number of alveoli
• Alveoli


  The sites of gas exchange where gases diffuse in and out of the bloodstream
• Alveoli


  • Have a huge surface area
  • Have very thin walls so the diffusion path is very short
  • Have a very good blood supply so oxygen is rapidly removed and the concentration gradient is steep
• Oxygen in the air


  Diffuses into the bloodstream
• Carbon dioxide in the bloodstream

  Diffuses out into the air
• Breathing increases the rate of diffusion by bringing fresh oxygen into the alveoli and taking away carbon dioxide