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Steps of Pulmonary Ventilation (Inspiration (Inspiratory muscles contract,…
Steps of Pulmonary Ventilation
Inspiration
Inspiratory muscles contract
Thoracic cavity volume increases
Intrapulmonary volume increases
Intrapulmonary pressure decreases
The intrapulmonary pressure now decreases, due to the volume increase cause by the chest wall expanding. Now, intrapulmonary pressure is lower than atmospheric pressure, so air moves down the pressure gradient into the lungs. Air will continue to enter the lungs until intrapulmonary and atmospheric pressure are equal.
The lungs are stretchy and move with the chest wall, so since the chest wall is expanding at this time during inspiration, the intrapulmonary volume increases.
Due to the actions of the external intercostal muscles, the volume of the thoracic cavity increases.
During this step, the diaphragm moves inferiorly and flattens out. The external intercostals also lift the rib cage, which causes the ribs to move outward and upward, along with the sternum moving superiorly.
Expiration
Inspiratory muscles relax
Thoracic cavity volume decreases
Intrapulmonary volume decreases
Intrapulmonary pressure increases
The intrapulmonary pressure now increases due to the intrapulmonary volume decreasing, so the intrapulmonary pressure is now higher than atmospheric pressure. Air now moves down its pressure gradient and leaves the lungs. Air will continue to leave the lungs until intrapulmonary and atmospheric pressure are equal.
Sine the lungs move with the chest wall, and the chest wall has now decreased it volume, intrapulmonary volume decreases as well.
Due to the external intercostal muscles relaxing and the recoiling stroma, the volume of the thoracic cavity decreases
During this step, the diaphragm becomes rounded and moves superiorly. The external intercostals allow the rib cage to move inward and move inferiorly, and the sternum moves posteriorly.
Deep Inspiration
Forced Expiration
This is when air is quickly and forcefully moved out of the lungs due to a sharp change in intrapulmonary pressure. It occurs when the muscles of the abdominal wall contract and the intra-abdominal pressure depresses the rib cage.
This is when a larger change in the intrapulmonary volume is created. Using the accessory respiratory muscles, a larger pressure gradient can be created, which pulls more air into the lungs.
Factors Influencing Pulmonary Ventilation
Airway Resistance
Surface Tension of Alveolar Fluid
Compliance
Compliance relates to the stretchiness of the stroma, and any condition that decreases lung compliance will make the lungs harder to inflate, so it will make breathing harder and very exhausting.
This is when the water in the alveolar fluid will want to form a droplet as air exits the alveolus. This is a problem because it will collapse the alveolus, and a collapsed alveolus is harder to inflate than a partially inflated alveolus. The presence of surfactant decreases the surface tension in the alveolar fluid.
Airway resistance is any condition that slows or even blocks airflow. The more obstructed the airway, the lower or less the airflow will be.
Inspiration is the normal ventilation process in which air moves into the lungs.
Expiration is the normal ventilation process in which air moves out of the lungs.