Ventilation

Question 1

Inhalation steps

Answer 1

• diaphragm contracts (moves downwards / flattens)
• external intercostal muscles contract
• rib cage moves upwards and outwards
• increased volume of thoracic cavity
• decreased pressure of thoracic cavity
• pressure of thoracic cavity < atmospheric pressure (of rest of body)
• so air rushes into lungs / thoracic cavity through nose / mouth

Question 2

Exhalation steps

Answer 2

• external intercostal muscles relax
• rib cage moves downwards and inwards
• diaphragm stays convex / relaxes:
• decreased volume of thoracic cavity
• increased pressure of thoracic cavity
• pressure of thoracic cavity > atmospheric pressure (of rest of body)
• so air rushes out of lungs