Ventilation

• What is inspiration?

  breathing in
• What is expiration?

  breathing out
• How do the diaphragm and intercostal muscles allow air to move into the lungs during inspiration?

  - diaphragm contracts and flattens

  - external intercostal muscles contract pulling the ribcage up and out

  - this increases the volume of the thoracic cavity

  - the pressure in the thoracic cavity decreases below atmospheric pressure

  - air flows down the pressure gradient into the lungs
• How do the diaphragm and intercostal muscles allow air to move out of the lungs during expiration? (at rest)

  - diaphragm relaxes and domes upwards

  - external intercostal muscles relax and pull the ribcage down and in

  - this reduces the volume of the thorax

  - pressure in the thorax increases above atmospheric pressure

  - air flows down the pressure gradient out of the lungs
• What happens during expiration during exercise that does not occur at rest?

  - internal intercostal muscles contract

  - this pulls the ribcage down and in

  - abdominals contract

  - this causes the diaphragm to dome upwards further