Ventilation in lungs

• Pathway of air:

  1. Mouth and nose
  2. Trachea (windpipe)
  3. Bronchi
  4. Bronchioles
  5. Alveoli
• Pathway of air:

  Air flows in through the mouth and nose, then down the trachea (windpipe). The trachea then splits into two bronchi which branch off further into smaller tubes known as bronchioles. Bronchioles end in small air sacs known as alveoli. Alveoli are surrounded by capillaries; this is where gas exchange takes place
• The diaphragm, ribs and intercostal muscles help move air in and out of the lungs (ventilation)
• Each lung is surrounded by a membrane and the space (pleural cavity) is filled with pleural fluid. This lubricates the lungs and helps the lungs adhere to the walls of the thoracic cavity by water cohesion.

  • This allows the lungs to expand with the chest during inhalation
• Inspiration:

  1. Diaphragm contracts (moves down)
  2. External intercostal muscles contract, pulling ribcage up and out
  3. Increases the volume of the thoracic cavity which reduces air pressure because there is more space
  4. Air moves into the trachea down the pressure gradient (high to low)
  5. ACTIVE PROCESS - Requires energy
• Expiration:

  1. Diaphragm relaxes (moves up)
  2. External intercostal muscles relax, ribcage moves in and down
  3. Decreases volume of the thoracic cavity which increases the air pressure because there is less space
  4. Air moves out of the trachea down the pressure gradient
  5. Normal expiration (not forced) is a PASSIVE PROCESS