Breathing

• Respiration is a chemical reaction which releases energy from food
• The respiratory system exchanges the gases which are involved in respiration
• Respiratory system


  • Allows air to enter the body through the nasal cavity
  • Air flows into the trachea, bronchi, bronchioles, and alveoli
  • Facilitates gas exchange
• Breathing in (inspiration)


  1. Intercostal muscles contract, pulling the ribcage upwards and outwards

  2. Diaphragm contracts, pulling downwards and flatterns

  3. Volume of the thorax increases and the pressure inside decreases

  4. Air is drawn into the lungs down a pressure gradient
• Breathing out (expiration)


  1. Intercostal muscles relax, pulling the ribcage downwards and inwards

  2. Diaphragm relaxes, doming upwards into a dome shape

  3. Volume of the thorax decreases and the pressure inside increases

  4. Air is pushed out of the lungs into trachea
• Trachea


  • Has cartilage rings in the walls to keep it open
  • Has ciliated epithelium and goblet cells to clean the air before it reaches the lungs
• Goblet cells


  Produce mucus which traps dust, dirt and bacteria to prevent them entering the lungs
• Cilia


  Small hairs which beat to push the mucus back up the trachea so it can be swallowed and destroyed in the stomach
• Clean air then enters the two bronchi, one bronchus going to each lung
• The bronchi in the lungs split into smaller and smaller tubes called bronchioles
• The bronchioles end in microscopic air sacs called alveoli
• Bell jar model


  • Represents the thorax
  • Air only able to enter via the glass tube which represents the trachea
  • As the rubber sheet (diaphragm) is pulled down, the volume of the jar increases, the pressure decreases and air is drawn in through the glass tube inflating the balloons (lungs)
• Similarities between bell jar model and respiratory system

  • Glass tube/trachea allows air to pass through and splits into two
  • Balloons/lungs can inflate and deflate, are elastic like the alveoli
  • Rubber sheet/diaphragm can be domed up to decrease the volume in the jar
• Differences between bell jar model and respiratory system

  • Glass tube is rigid and inflexible unlike the cartilage bound trachea
  • Bell jar is unable to move, the ribs can move up and out to increase the volume of the thorax
  • Balloons are large open spaces whereas the lungs are made up of millions of individual elastic alveoli
  • Diaphragm only flattens, it is not pulled downwards like the rubber sheet