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A person can hold his breath longer if he gradually exhales than if he keeps his lungs fully expanded. This phenomenon is due to the fact that ____________________.
A. The concentration of $CO_2$ in the blood decreases, lessening the excitatory input to the carotid bodies
B. He is then using less $O_2$ , as his thoracic muscles are not working as hard
C. Stretch receptors in his lungs are then not firing as much thus lessening the excitatory input to the expiratory centres
D. He is preventing the pressure in his lungs from increasing too much

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Last updated date: 21st Jun 2024
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Answer
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Hint:-The way your body takes in oxygen and gets rid of carbon dioxide is by the process of inhalation and exhalation. A broad dome-shaped muscle below your lungs, known as the diaphragm, helps the mechanism. Your diaphragm pulls downward as you breathe in, producing a vacuum that allows a rush of air into your lungs.

Complete answer:
Pulmonary Stretch Receptors are a form of mechanoreceptor that senses as well as reacts to the physical expanding of the airways in the bronchial smooth muscle. Stretching and hence activation of the receptors of the pulmonary stretch leads to their increased afferent production, which tends to reduce the respiratory rate by extending the duration of expiration to a large degree.
During broad breaths, pulmonary stretch receptors present in the smooth muscle of the airways react to excessive lung stretching. When triggered, they send the potential for action to the inspiratory region in the medulla and apneustic center of the pons through broad myelinated fibers of the vagus nerve. Inspiratory discharge is inhibited by these impulses. A slowdown of respiratory frequency by increasing expiratory time is the key consequence of stimulating certain receptors. In reaction to a range of stimuli, such as lung inflation or deflation, respiratory irritants, and likely airway edema, rapidly adjusting pulmonary stretch receptors (RARs) initiate defensive reflexes located in the airways.
Thus, the right option is C.

Note:- In humans, the different forms of breathing include internal breathing, external breathing, and cellular breathing. Internal respiration involves the exchange of gases through blood and cells, while external respiration is the breathing cycle, while cellular respiration is the energy-producing metabolic reactions inside the cells.