Assertion (A): An increase in the volume of the thoracic cavity causes a similar increase in the pulmonary volume. Reason (R): We can directly alter…

The correct option is

A is true but R is false

.

Explanation

The mechanism of breathing relies on creating pressure gradients between the lungs and the atmosphere. This is achieved by changing the volume of the thoracic cavity, which mechanically influences the pulmonary volume due to the anatomical structure of the respiratory system.

Statement-wise Analysis:

• Assertion (A): Correct. The lungs are situated in the thoracic chamber, which is anatomically an air-tight compartment formed by the vertebral column, sternum, ribs, and diaphragm. Because of this close anatomical coupling, any change in the volume of the thoracic cavity is immediately reflected in the pulmonary (lung) cavity. Therefore, an increase in thoracic volume leads to a similar increase in pulmonary volume.
• Reason (R): Incorrect. Humans cannot directly alter the pulmonary volume. The lungs themselves do not possess intrinsic skeletal muscles to actively expand or contract their volume. Instead, breathing movements are generated by the contraction and relaxation of the diaphragm and intercostal muscles (external and internal). These muscles alter the thoracic volume, and the lungs passively expand or recoil in response.

Key Takeaway:

Breathing is a mechanical process where pulmonary volume changes are passive consequences of thoracic volume alterations driven by the diaphragm and intercostal muscles.