Question

Name the respiratory muscles, and describe how they are involved in normal inhalation and exhalation. Define these pressures and relate them to a cycle of breathing: atmospheric pressure, intrapulmonic pressure. (pp. \(353-354\) )

Short answer

Answer: The main respiratory muscles involved in inhalation and exhalation are the diaphragm and the intercostal muscles. During inhalation, the diaphragm contracts and moves downward, while the external intercostal muscles contract and cause the ribcage to move upward and outward. This creates a negative pressure in the thoracic cavity, reducing intrapulmonic pressure and allowing airflow into the lungs. During exhalation, these muscles relax, causing the ribcage to move downward and inward, increasing intrapulmonic pressure and expelling air from the lungs. This continuous process of inhalation and exhalation maintains the balance of gases within the respiratory system, constantly equalizing the intrapulmonic pressure with the atmospheric pressure.

Step-by-step solution

Name the respiratory muscles

The main respiratory muscles involved in the process of inhalation and exhalation are the diaphragm and the intercostal muscles. The diaphragm is a large, dome-shaped muscle located at the base of the lungs and above the abdominal cavity. The external and internal intercostal muscles are found between the ribs in the thoracic cavity (anterior and posterior parts, respectively).

Describe the involvement of the respiratory muscles in inhalation

During normal inhalation, the diaphragm contracts and moves downward. This contraction creates a negative pressure within the thoracic cavity, causing the lungs to expand and draw in air. Simultaneously, the external intercostal muscles contract, causing the ribcage to move upward and outward, thus further expanding the thoracic cavity. This expansion increases the lung volume and reduces the intrapulmonic pressure, allowing for air to flow into the lungs to equalize the pressure.

Describe the involvement of the respiratory muscles in exhalation

During normal exhalation, the diaphragm and external intercostal muscles relax, causing the ribcage to move downward and inward. As the ribcage moves inwards, the lung volume decreases, and intrapulmonic pressure increases. The increase in intrapulmonic pressure causes air to flow out of the lungs until the intrapulmonic pressure is equal to the atmospheric pressure, completing the exhalation process.

Define atmospheric pressure and intrapulmonic pressure

Atmospheric pressure refers to the pressure exerted by the weight of the surrounding air. The atmospheric pressure at sea level is approximately \(760\) mmHg. Intrapulmonic pressure, also known as alveolar pressure, refers to the pressure within the lungs, specifically within the small air sacs (alveoli) where gas exchange occurs.

Relate the pressures to a cycle of breathing

At the beginning of the inhalation process, atmospheric pressure and intrapulmonic pressure are equal, and there is no movement of gases between the external environment and the lungs. As the diaphragm and external intercostal muscles contract, negative pressure in the thoracic cavity lowers the intrapulmonic pressure, causing air to flow into the lungs to equalize the pressures. During exhalation, the relaxation of the respiratory muscles causes a decrease in lung volume, increasing the intrapulmonic pressure higher than the atmospheric pressure. As a result, air will flow out of the lungs until the intrapulmonic and atmospheric pressures are equal once again. This continuous process of inhalation and exhalation maintains the balance of gases within the respiratory system.