Systems Biology
The breathing cycle consists of the inspiratory phase and the expiratory phase. The pressure gradient created by the difference between the pressure inside the lungs versus the pressure outside the lungs drives air to flow in and out. This principle can be understood through Boyle's Law, which describes the inverse relationship between pressure and volume.
During the inspiratory phase, an active process involving muscle contractions of the diaphragm and external intercostal muscles, creates more space in the thoracic cavity. As a result, there is more volume in the lungs, decreasing the pressure inside them. Air flows into the lungs until the pressure inside the lungs equals atmospheric pressure. On the other hand, passive expiration is driven by relaxation of the diaphragm and external intercostal muscles, causing a decrease in volume and an increase in pressure. Air flows out of the lungs until the pressure inside is the same as the pressure outside. During forced expiration, the abdominal and internal intercostal muscles contract, decreasing the volume of the thoracic cavity and lungs, resulting in a higher pressure gradient and forcing air out quickly.
Lesson Outline
<ul> <li>Breathing cycle <ul> <li>Inspiratory phase</li> <li>Expiratory phase</li> </ul> <li>Pressure gradient drives air flow</li> <ul> <li>Caused by difference in pressure inside and outside lungs</li> <li>Explained by Boyle's Law (inverse relationship between pressure and volume)</li> </ul> </li> <li>Inspiratory phase <ul> <li>Active process involving muscle contractions</li> <ul> <li>Diaphragm and external intercostal muscles</li> </ul> <li>More space created in thoracic cavity</li> <li>Increased volume in lungs decreases pressure</li> <li>Air flows in until lung pressure equals atmospheric pressure</li> </ul> </li> <li>Expiratory phase <ul> <li>Two types:</li> <ul> <li>Passive expiration</li> <li>Forced expiration</li> </ul> <li>Passive expiration</li> <ul> <li>Driven by relaxation of diaphragm and external intercostal muscles</li> <li>Decreased volume and increased pressure</li> <li>Air flows out until lung pressure equals atmospheric pressure</li> </ul> <li>Forced expiration</li> <ul> <li>Abdominal and internal intercostal muscles contract</li> <li>Decreased volume of thoracic cavity and lungs</li> <li>Higher pressure gradient forces air out quickly</li> </ul> </ul> </li> </ul>
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FAQs
The breathing cycle consists of the inspiratory phase and the expiratory phase. The inspiratory phase is when air is inhaled into the lungs, and it involves the contraction of the diaphragm and the external intercostal muscles. These muscle contractions increase thoracic volume, causing a decrease in pressure within the thoracic cavity according to Boyle's Law. This pressure gradient between the atmospheric pressure and the pressure inside the thoracic cavity promotes airflow into the lungs. The expiratory phase is when air is exhaled from the lungs, usually through passive expiration. During this phase, the diaphragm and external intercostal muscles relax, decreasing thoracic volume and increasing the pressure within the thoracic cavity, causing air to flow out of the lungs.
Boyle's Law states that the pressure of a gas is inversely proportional to its volume, assuming constant temperature. In the context of the breathing cycle, Boyle's Law explains the relationship between thoracic volume and pressure within the thoracic cavity. During the inspiratory phase, the contraction of the diaphragm and external intercostal muscles increases thoracic volume, which in turn decreases the pressure within the thoracic cavity according to Boyle's Law. Conversely, during the expiratory phase, the relaxation of these muscles decreases thoracic volume, increasing the pressure within the thoracic cavity. These pressure changes create a pressure gradient that drives airflow in and out of the lungs.
The diaphragm is a major muscle involved in the breathing cycle. It is a dome-shaped sheet of muscle that separates the thoracic cavity from the abdominal cavity. When the diaphragm contracts during the inspiratory phase, it flattens and moves downward. This action increases the volume of the thoracic cavity, decreasing intrathoracic pressure and creating a pressure gradient that draws air into the lungs. During the expiratory phase, the diaphragm relaxes and returns to its original dome shape, reducing the volume of the thoracic cavity and increasing intrathoracic pressure, which aids in expelling air from the lungs.
External intercostal muscles are located between the ribs and play an essential role in the breathing cycle, specifically during the inspiratory phase. When these muscles contract, they lift the ribs upward and outward, further increasing the volume of the thoracic cavity. This increase in volume leads to a decrease in intrathoracic pressure, as described by Boyle's Law, creating a pressure gradient that draws air into the lungs. During the expiratory phase, the external intercostal muscles relax, allowing the ribs to move downward and inward, decreasing thoracic volume and facilitating air expulsion from the lungs.
Passive expiration is the process of exhaling air from the lungs without the use of active muscular effort. During passive expiration, the diaphragm and external intercostal muscles relax, resulting in a decrease in thoracic volume. According to Boyle's Law, this decrease in volume leads to an increase in intrathoracic pressure, which surpasses the atmospheric pressure outside the body. This pressure gradient causes air to flow out of the lungs and complete the expiratory phase of the breathing cycle. Passive expiration is the dominant mode of exhalation during rest and normal activities, while active expiration, involving additional muscles, occurs during rigorous physical activity or forced exhalation.
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