Question

Which of the following is not associated with respiratory system?

• A. Ciliated nasal membranes warm, moisten, and filter inspired air
• B. Contraction of the diaphragm enlarges the thoracic cavity
• C. When the thoracic cavity enlarges, the pressure of air within the lungs fails
• D. When the pressure of air within the lungs is less than the atmospheric pressure, air will flow out of the lungs
• E. The respiratory process consists of inspiratory and expiratory acts following one another

Answer 1

The correct option is D When the pressure of air within the lungs is less than the atmospheric pressure, air will flow out of the lungs

• The process of breathing ) is divided into two distinct phases, inspiration and expiration occur simultaneously.
  
• Inspiration can occur if the pressure within the lungs (intra-pulmonary pressure) is less than the atmospheric pressure,
• Inspiration is initiated by the contraction of a diaphragm which increases the volume of the thoracic chamber in the anteroposterior axis. The contraction of external inter-costal muscles lifts up the ribs and the sternum causing an increase in the volume of the thoracic chamber in the dorsoventral axis.
• The overall increase in the thoracic volume causes a similar increase in pulmonary volume. An increase in pulmonary volume decreases the intrapulmonary pressure to less than the atmospheric pressure which forces the air from outside to move into the lungs. Hence, When the pressure of air within the lungs is less than the atmospheric pressure, air will not flow out of the lungs.
  

So, the correct answer is 'When the pressure of air within the lungs is less than the atmospheric pressure, air will flow out of the lungs'.