Question

All of the following statements are true except
A. Contraction of diaphragm increases the volume of the thoracic cavity in the cephalocaudal axis
B. During normal breathing, intrapleural pressure is always subatmospheric
C. The high surface tension of alveolar surfactant facilities inhalation
D. Passive exhilaration results from the recoil of the chest wall and lungs

Answer 1

Hint: Inhalation and exhalation are two important events that occur during breathing. Both of these events cause some changes in the respiratory system in a rhythmic manner. The lungs expand during inhalation and contract during expiration.

Complete answer: Let us discuss each of the given statements in detail one by one.
Statement A: The diaphragm is one of the muscles used in breathing. During inspiration that is the intake of air, the expansion of the thoracic cavity occurs. The muscle fibres of the diaphragm are inserted into the sternum and lower ribs. During breathing, contraction of the diaphragm occurs that causes its dome to descend into the abdominal cavity. This results in the elongation of the thorax and a rise in volume. Thus, the statement saying that the contraction of the diaphragm increases the volume of the thoracic cavity in the cephalocaudal axis is true.
Statement B: The intrapleural pressure is referred to as the pressure that is present in the pleural cavity. Normally this pressure is slightly lower than the atmospheric pressure. It is known as negative pressure. At rest, the intrapleural pressure is always negative. Thus, this statement regarding the intrapleural pressure being always subatmospheric is false.
Statement C: The alveolar fluid lining has a lower surface tension than predicted by plasma air-interface. This results in an increase in pulmonary compliance and also lowers pulmonary work. The alveolar surface tension has a direct effect on the size of the alveoli. The lower the surface tension the more stabilized the alveoli become. This decreases the size of the alveoli. Thus, the high surface tension of alveolar surfactant facilitates inhalation by increasing the alveolar size. So, this statement is true.
Statement D: Passive exhilaration results from the recoil of the chest wall and lungs. The chest cavity shrinks and the chest wall becomes closer to the lungs by recoiling of chest wall muscles. This statement is also true.
Hence, from the above discussion, we can conclude that the right answer is option B.

Note: Breathing or respiration is a complex process involving hundreds of events occurring at once and in a rhythmic manner. Any disturbance in the working of even a single unit can result in lungs collapse. The atmospheric pressure is always higher than the intrapleural pressure. But in case of injury, they both become equal that causes lungs to collapse.