Expiration (exhalation)

• what type of process is breathing out?

  its mainly a passive process
• how does the process of expiration work?

  1. the external intercostal muscles relax
  2. the ribs move downwards and inwards
  3. at the same time, the diaphragm muscle relax, so the diaphragm domes upwards
  4. the pleural membranes move down and in with the ribs, and the lower parts move up with the diaphragm - the elastic properties of the lungs allow their volume to decrease, decreasing the volume inside the alveoli
  5. this increases the pressure in the lungs
  6. air pressure in the lungs is now greater than atmospheric pressure so air is forced of the lungs
• what is the main cause of air being forced out f the lungs during normal breathing?

  its because of the elastic recoil of the lungs
• what is a major characteristic of lung tissue and why is it important?

  • lung tissue is elastics and, like a stretched elastic band, lungs recoil and regain their original shape when not being actively expanded
  • this recoil plays a major part in pushing air out of the lungs
• what are the inside surfaces of the alveoli coated in?

  they are coated with surfactant, which can be thought of as a non-sticking mixture
• what is are the features of surfactant?

  • its made of moist secretions, containing phospholipid and protein
  • it has a low surface tension, preventing the alveoli collapsing during exhalation, when the air pressure inside them is low
  • it also allows for gases to dissolve, before they diffuse in or out
• what is the surfactant inside of alveoli made of?

  its made of moist secretion, containing phospholipids and protein
• whats is surfactant?

  a fluid lining the surface of the alveoli that reduces surface tension and preents collapse of the alveoli during exhalation