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Assertion: Inspiration occurs when there is a negative pressure in the lungs with respect to the atmospheric pressure.
Reason: During inspiration, a decrease in pulmonary volume increases the intrapulmonary pressure than atmospheric pressure which forces the air from outside to move into the lungs.
A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
C. Assertion is correct but Reason is incorrect
D. Both Assertion and Reason are incorrect

Last updated date: 20th Jun 2024
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Hint: Inspiration or inhalation is the first step. The diaphragm shrinks and pulls back as you inhale the lungs. The muscles between the ribs simultaneously contract and pull up. The thoracic cavity is increased in size and the internal pressure decreases.

Complete answer: Two breathing cycles are inspiration and expiration. The phase of intake of air is inspiration and expiration are the air breath. The volume of the thoracic region rises during inspiration. The diaphragm is flattened and the intercostal muscles are relaxed. This causes the thoracic cavity to increase and lung expansion and air to take in. The dome form of the diaphragm and the contraction of the intercostal muscles decreases in the volume of the thoracic cavity during expiry. The lungs will thus force the air out. Air is moved in and out of the lungs, producing a pressure gradient from the lungs to the atmosphere. Inspiration is created when the pressure within the lungs is less than the ambient stress (intrapulmonary pressure); i.e., the atmospheric pressure in the lungs is negative. Inspiration is caused by diaphragm contraction which increases the chamber volume of the anteroposterior axis. The external contraction of the intercostal muscles elevates the ribs and the sternum which increases the thoracic chamber volume of the dorso-ventral axis. The overall rise in thoracic volume causes the pulmonary volume to increase. Increasing pulmonary volume reduces the intrapulmonary pressure which is less than the air pressure which causes the air to move into the lungs from the outside.
The right choice is, therefore, C- Assertion is correct but Reason is incorrect.

Note: When the diaphragm, under the lungs, contracts (tight) and goes down, the regular breathing process begins. This improves the room in your chest cavity to expand your lungs. The air reaches your nose or mouth and is warm and humidified as the lungs expand. The key difference between inspiration and expiration is that the inhalation process is air in the lungs, while exhalation is the process of air escaping from the lungs.