SHEET Respiratory System Physiology Lab Time/Date Mechanics of Respiration 1. Base your answers to the following on your observations of the operation of the model lung. Under what internal conditions of the thoracic cavity does air tend to flow into the lungs? Under what internal conditions of the thoracic cavity does air tend to flow out of the lungs? Explain. 2. Activation of the diaphragm and the external intercostal muscles begins the inspiratory process. What effect does contraction of these muscles have on thoracic volume, and how is this accomplished? 3. What was the approximate increase in diameter of chest circumference during a quiet inspiration? inches During forced inspiration? inches 4. What temporary advantage does the substantial increase in chest circumference during forced inspiration create? Respiratory Volumes and Capacities: Spirometry 5. Write the respiratory volume term and the normal value that is described by the following statements: Volume of air present in the lungs after a forceful expiration Volume of air that can be expired forcibly after a normal expiration Volume of air that is breathed in and out during a normal respiration Volume of air that can be inspired forcibly after a normal inspiration Volume of air corresponding to TV + IRV + ERV 307
The correct answer and explanation is:
1. Air Flow into and Out of the Lungs:
Air flows into the lungs when the pressure inside the thoracic cavity (intrapulmonary pressure) is lower than the atmospheric pressure. This happens during inspiration when the diaphragm and external intercostal muscles contract, expanding the thoracic cavity. The expansion of the lungs causes a decrease in intrapulmonary pressure, allowing air to flow in.
Conversely, air flows out of the lungs when the pressure inside the thoracic cavity is higher than the atmospheric pressure. This occurs during expiration, typically a passive process, where the diaphragm and intercostal muscles relax, causing the chest to decrease in volume. The reduced volume leads to an increase in intrapulmonary pressure, driving air out of the lungs.
2. Effect of Diaphragm and Intercostal Muscle Contraction on Thoracic Volume:
Contraction of the diaphragm and external intercostal muscles increases thoracic volume. The diaphragm contracts and flattens, increasing the vertical dimension of the thoracic cavity. Simultaneously, the external intercostals contract, elevating the ribs and increasing the transverse dimension of the thoracic cavity. Together, these actions create more space within the thoracic cavity, lowering the pressure inside and allowing air to flow into the lungs.
3. Chest Circumference Changes During Inspiration:
- Quiet Inspiration: During quiet inspiration, the chest circumference typically increases by about 1-2 inches, as the diaphragm and external intercostal muscles expand the thoracic cavity.
- Forced Inspiration: During forced inspiration, the chest circumference increases by a larger amount, around 3-4 inches, due to more forceful contraction of the respiratory muscles, including the diaphragm and accessory muscles like the sternocleidomastoid and scalenes.
4. Temporary Advantage of Forced Inspiration:
The substantial increase in chest circumference during forced inspiration allows for a greater intake of air. By expanding the thoracic cavity more significantly, the lungs can increase their volume more than during normal, quiet breathing, providing an advantage during activities requiring increased oxygen intake, such as exercise or during physical exertion.
5. Respiratory Volumes and Capacities:
Here are the respiratory volume terms and their normal values:
- Residual Volume (RV): Volume of air remaining in the lungs after a forceful expiration. Normally about 1,200 mL.
- Expiratory Reserve Volume (ERV): Volume of air that can be expired forcibly after a normal expiration. Typically 1,200 mL.
- Tidal Volume (TV): Volume of air that is breathed in and out during a normal respiration. This is usually around 500 mL.
- Inspiratory Reserve Volume (IRV): Volume of air that can be inspired forcibly after a normal inspiration. Typically 3,000 mL.
- Vital Capacity (VC): The volume of air corresponding to TV + IRV + ERV. This value can range from 4,000 to 5,000 mL in a healthy adult.
These volumes together help describe the efficiency and functionality of the respiratory system during different breathing conditions.