The Mechanism of Breathing

• What is ventilation?


  The process of air moving in and out of the lungs.
• What does ventilation maintain?

  The diffusion of gases across the alveolar epithelium.
• What is inspiration (inhalation)?

  When air is forced into the lungs as the air pressure of the atmosphere is greater than the air pressure inside the lungs.
• What is expiration (exhalation)?

  When air is forced out of the lungs as the air pressure in the lungs is greater than that os the atmosphere.
• What are the pressure changes in the lungs brought about by?

  The movement of the diaphragm, internal intercostal muscles and external intercostal muscles.
• What is the diaphragm?

  A sheet of muscle that separates the thorax from the abdomen.
• Where do the intercostal muscles lie?

  Between the ribs.
• What are the two sets of intercostal muscles?

  Internal intercostal muscles and external intercostal muscles.
• What does the contraction of the internal intercostal lead to?

  Expiration / exhalation.
• What does the contraction of the external intercostal lead to?

  Inspiration / inhalation.
• What process is breathing and why?

  An active process as it used energy.
• What do the intercostal muscles do during inspiration?

  The external intercostal muscles contract while the internal intercostal muscles relax.
• What happens to the ribs during inspiration?

  They are pulled upwards and outwards.
• What do the diaphragm muscles do during inspiration?

  They contract which causes the diaphragm to flatten.
• What increases the volume during inspiration?

  The ribs being pulled up and out, and the diaphragm flattening.
• What does an increased volume in the thorax result in during inspiration?

  A reduction of pressure in the lungs.
• What does a reduced pressure in the lungs mean during inspiration?

  That the atmospheric pressure is now greater than the lungs so air is forced in.
• What process is breathing out and why?

  A passive process as it doesn't require much energy.
• What do the intercostal muscles do during expiration?


  The internal intercostal muscles contract while the external intercostal muscles relax.
• What happens to the ribs do during expiration?


  They move downwards and inwards.
• What do the diaphragm muscles do during expiration?


  They relax and so the diaphragm is pushed up again by the continents of the abdomen that were compressed during inspiration.
• What decreases the volume during expiration?


  The ribs being pulled down and in, and the diaphragm relaxing.
• What does a decreased volume in the thorax result in during expiration?


  An increase of pressure in the lungs.
• What does an increased pressure in the lungs mean during expiration?


  The lung pressure is now greater than that of the atmosphere so air is forced out.
• What is the main cause of air being forced out during normal quiet breathing?

  The recoil of the elastic tissue in the lungs.