Final answer:
Contraction of the chest wall creates a driving force which enables air to flow into the lungs, making the correct answer A) Contraction, driving force
Step-by-step explanation:
Contraction of the chest wall creates a difference between alveolar pressure (Pa) and pleural pressure (Ppl), which is the driving force for air to flow into the lungs. Therefore, the correct answer is A) Contraction, driving force.
Pulmonary ventilation involves two primary processes: inspiration and expiration. During inspiration, the diaphragm contracts and the external intercostal muscles raise the ribs, thereby expanding the thoracic cavity. This expansion decreases the pressure inside the thoracic cavity relative to atmospheric pressure, creating a pressure gradient that allows air to flow into the lungs.
Detailed understanding of thoracic mechanics shows that inspiration is an active process involving muscle contraction, while expiration is mostly passive, particularly during gentle exhalation, with the elastic recoil of the lungs assisting in expelling air.