Final Answer:
b) Normally, expiration is a passive process, statement about expiration are correct
Step-by-step explanation:
b) Normally, expiration is a passive process primarily driven by the elastic recoil of the lungs and chest wall. During inhalation, the diaphragm contracts and the external intercostal muscles expand the thoracic cavity, causing a decrease in intrathoracic pressure. However, during expiration, these muscles relax, allowing the chest wall and lungs to return to their resting position. This recoil leads to an increase in intrathoracic pressure, facilitating the expulsion of air from the lungs.
The statement "The diaphragm contracts during expiration" (option a) is incorrect. The diaphragm actually relaxes during expiration. This relaxation contributes to the passive recoil of the lungs and chest wall. Alveolar pressure increases during expiration, opposing the statement in option c.
As the intrathoracic pressure rises, alveolar pressure increases, causing air to move out of the lungs. Lastly, the statement "The abdominal muscles contract during normal expiration" (option d) is incorrect. Abdominal muscles play a role in forced expiration, but during normal expiration, they remain relatively passive as the elastic recoil of the lungs and chest wall dominates the process.
Understanding the mechanics of breathing is crucial for comprehending respiratory physiology. The passive nature of expiration ensures efficient gas exchange without excessive energy expenditure, highlighting the adaptability and efficiency of the respiratory system in maintaining homeostasis.