What is the main role of thoracic expansion during respiration?

• A. To increase blood circulation
• B. To facilitate gas exchange
• C. To create negative pressure for pulmonary ventilation
• D. To stimulate vocal cord vibration

Answer: (C)

The primary role of thoracic expansion during respiration is to create negative pressure for pulmonary ventilation. When the thoracic cavity expands, it decreases the pressure within the lungs compared to the external atmospheric pressure. This negative pressure allows air to flow into the lungs, facilitating the process of inhalation.

As the diaphragm contracts and the rib cage expands, the increase in volume of the thoracic cavity results in this pressure differential. Air naturally moves from areas of higher pressure (outside the body) to areas of lower pressure (inside the lungs), driving the process of breathing.

The other options, while related to aspects of respiration and may involve thoracic movements, do not capture the fundamental mechanical role of thoracic expansion specifically in creating the conditions necessary for air to enter the lungs.