Question

Use the words inspiration or expiration to describe the part of the breathing cycle that occurs as a result of each of the following: a. The diaphragm contracts (flattens out). b. The volume of the lungs decreases. c. The pressure within the lungs is less than that of the atmosphere.

Short answer

a. Inspirationb. Expirationc. Inspiration

Step-by-step solution

Identifying the process when the diaphragm contracts

When the diaphragm contracts, it moves downward and flattens, increasing the volume of the thoracic cavity. This causes air to flow into the lungs as the pressure inside decreases. This part of the breathing cycle is called inspiration.

Analyzing the volume decrease of the lungs

When the volume of the lungs decreases, the air pressure within the lungs increases, causing air to be expelled out of the lungs. This part of the breathing cycle is called expiration.

Comparing internal and external pressure

When the pressure within the lungs is less than that of the atmosphere, air is drawn into the lungs due to the pressure gradient. This occurs during the process of inspiration.

Key concepts

Inspiration

Inspiration, also known as inhalation, is the process of drawing air into the lungs. This occurs when the diaphragm contracts and moves downward, expanding the thoracic cavity.
As the thoracic cavity volume increases, the pressure within it decreases, causing air to flow into the lungs to balance the pressure difference.
During inspiration:

• The diaphragm contracts and flattens.
• The ribcage expands as the intercostal muscles contract.
• Air pressure inside the lungs decreases compared to atmospheric pressure.
• Air is drawn into the lungs.

Inspiration is a vital part of the breathing cycle and ensures that fresh oxygen enters the lungs for gas exchange.

Expiration

Expiration, or exhalation, is the process of expelling air out of the lungs. This generally happens when the diaphragm relaxes and moves upward into a dome shape, reducing the volume of the thoracic cavity.
As the thoracic cavity volume decreases, the pressure inside increases, forcing air to flow out of the lungs.
During expiration:

• The diaphragm relaxes and curves upward.
• The ribcage contracts as the intercostal muscles relax.
• Air pressure inside the lungs increases compared to atmospheric pressure.
• Air is pushed out of the lungs.

Expiration allows the removal of carbon dioxide from the body and is essential for maintaining effective gas exchange.

Lung Volume

Lung volume refers to the different capacities of the lungs at various stages of the breathing cycle. The main volumes to consider include tidal volume, inspiratory reserve volume, expiratory reserve volume, and residual volume.

• Tidal Volume (TV): The amount of air inhaled or exhaled during normal breathing.
• Inspiratory Reserve Volume (IRV): The additional air that can be inhaled after a normal inspiration.
• Expiratory Reserve Volume (ERV): The additional air that can be exhaled after a normal expiration.
• Residual Volume (RV): The air remaining in the lungs after a forceful expiration.

Understanding lung volume helps in assessing lung function and diagnosing respiratory conditions.

Diaphragm

The diaphragm is a dome-shaped muscular partition located below the lungs that plays a crucial role in breathing. It separates the thoracic cavity from the abdominal cavity and assists in respiration by contracting and relaxing.

• When the diaphragm contracts, it flattens and moves downward, increasing the volume of the thoracic cavity for inspiration.
• When the diaphragm relaxes, it moves upward into a dome shape, reducing the thoracic cavity volume for expiration.

The diaphragm is controlled by the phrenic nerve and is essential for efficient breathing.
Proper diaphragm function is vital for respiratory health.

Thoracic Cavity Pressure

Thoracic cavity pressure refers to the pressure within the chest cavity that surrounds the lungs. It changes during the breathing cycle to facilitate airflow into and out of the lungs.
During inspiration, the expansion of the thoracic cavity leads to a decrease in pressure, creating a negative pressure gradient that draws air into the lungs.
During expiration, the reduction in thoracic cavity volume increases the pressure, pushing air out of the lungs.
Maintaining appropriate thoracic cavity pressure is essential for effective breathing and ensures that oxygen and carbon dioxide are exchanged efficiently. Any disruption in this pressure balance can lead to respiratory difficulties.

• Negative pressure during inhalation helps in drawing air into the lungs.
• Positive pressure during exhalation helps in expelling air from the lungs.