Breathing

• Respiration


  A chemical reaction which releases energy from food
• Respiratory system


  Exchanges the gases which are involved in respiration
• Structures in the human thorax


  • Ribs
  • Upper backbone
  • Organs found in the chest
• Trachea


  The major airway in the respiratory system, also known as the windpipe, connecting the pharynx and larynx to the lungs
• Bronchi


  The two major air tubes in the lungs
• Bronchioles


  The many small, branching tubules into which the bronchi subdivide
• Alveoli


  Tiny air sacs in the lungs, where gas is exchanged during breathing
• Structures required for ventilation


  • Ribs
  • Intercostal muscles
  • Diaphragm
• Diaphragm


  A large sheet of muscle that separates the lungs from the abdominal cavity
• Trachea


  • Cartilage rings in the walls help to keep it open
  • 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
• Breathing in (inspiration)


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

  2. Diaphragm contracts, pulling downwards

  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

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

  4. Air is pushed out of the lungs
• The bell jar model represents the process of ventilation as a series of changes in pressure within the thorax
• Similarities between the bell jar model and the respiratory system


  • Glass tube and trachea allows air to pass through and splits into two
  • Bell jar and chest cavity is air tight
  • Balloons and lungs can inflate and deflate, are elastic like the alveoli
  • Rubber sheet anddiaphragm can be domed up to decrease the volume in the jar
• Differences between the bell jar model and the 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