Asked Nov 9, 2019

Explain the changes in the atmospheric and intrapulmonary air pressure, muscle contraction, lungs and thoracic cavity during inspiration and expiration 


Expert Answer

Step 1

The act of inspiration and expiration is known as pulmonary ventilation. The main mechanisms involved in the process of pulmonary ventilation are atmospheric pressure, alveolar pressure and the intrapleural pressure.

Step 2

The entry and exit of air into and out of the lungs depend on its pressure between atmosphere and the lungs. The movement of gas molecules is from their higher concentration to their lower concentration. The relationship between the volume and pressure of the air is described by Boyle’s law which states that the pressure of gas is inversely proportional to its volume.

Atmospheric pressure is defined as the amount of pressure exerted by the gases in air present around the body and is expressed in unit atmosphere.  The interpulmonary pressure (the pressure of gases in lungs) is always in equilibrium with the pressure of gases in the atmosphere in normal scenario.

Step 3

During the inhalation, the muscles of thoracic cavity (external intercoastal and muscles of diaphragm) contracts and enlarges the area of thoracic cavity. Contraction of diaphragm flattens it and that of external intercoastal muscles, elevates the rib cage. When the volume of thoracic cavity increases, the interpulmonary pressure will decrease as compared to the atmospheric cavity (according to Boyle’s law).

During exhalation (pas...

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