Ventilation

Question 1

How does inspiration work?

Answer 1

1) Contraction of diaphragm (pulled down) and contraction of external intercostal muscles - ribs and sternum are raised.
2) Volume increase in thoracic activity.
3) Air pressure in thorax decreases below atmospheric pressure.
4) Air flows into the lungs, down the pressure gradient.
5) Thoracic and atmospheric pressure is at equilibrium.

Question 2

How does expiration work?

Answer 2

1) Relaxation of the diaphragm (pushed up by displaced organs and contraction of internal intercostal muscles - ribs and sternum are lowered.
2) Volume decrease in thorax.
3) Air pressure in thorax increases above atmospheric pressure.
4) Air flows out of the lungs due to pressure gradient aided by elastic recoil of alveoli.
5) Thoracic and atmospheric pressure is at equilibrium.