6.6 - Ventilation

Question 1

What happens during expiration? (5)

Answer 1

1. The external intercostal muscles relax, moving the ribcagedown and in.
2. The volume of the thoracic cavity decreases.
3. The diaphragm relaxes and unflattens, further decreasing the volume of the thoracic cavity.
4. The lung pressure increases above atmospheric pressure.
5. Air is forced out of the lungs down the pressure gradient.

• Elastic fibres in the alveoli also shrink and recoil back to their original shape when the thoracic cavity volume decreases.
• This increases the pulmonary pressure and helps to push air out of the lungs.

Question 2

What happens during inspiration? (5)

Answer 2

1. the external intercostal muscles contract while the internal intercostal muscles relax, moving the ribcage up and out
2. volume of the thoracic cavity increases
3. diaphragm contracts and flattens - further increases the volume of the throacic cavity
4. lung pressure decreases below atmospheric pressure
5. air flows into the lungs down the pressure gradient

Question 3

3 sets of muscles that act on the ribcage

Answer 3

1. the diaphragm - sheet of muscle that moves the ribcage up and out when it contracts
2. external intercostal muscles - found between the ribs and pull the ribcage up and out when they contract (inspiration)
3. internal intercostal muscles - found between the ribs and pull the ribcage down and in when they contract (expiration)

Question 4

What is ventilation?

Answer 4

the constant movement of air into and out of the lungs (inspiration and expiration)