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 relaxes, moving up into the thoracic cavity. b. The volume of the lungs expands. c. The pressure within the lungs is greater than that of the atmosphere.

Short answer

a. Expiration. b. Inspiration. c. Expiration.

Step-by-step solution

- Determine the effect of diaphragm relaxation

When the diaphragm relaxes, it moves up into the thoracic cavity. This decreases the volume of the thoracic cavity, leading to an increase in the pressure within the lungs compared to the atmosphere. This causes air to flow out of the lungs, which is called expiration.

- Analyze lung volume expansion

When the volume of the lungs expands, the pressure inside the lungs decreases. This lower pressure compared to the atmospheric pressure causes air to flow into the lungs. This process is referred to as inspiration.

- Examine greater lung pressure

If the pressure within the lungs is greater than the atmospheric pressure, air is pushed out of the lungs. This process is known as expiration.

Key concepts

Inspiration

Inspiration, or inhalation, is the process of drawing air into the lungs. This happens when the diaphragm contracts and moves downward, making space in the thoracic cavity. The intercostal muscles between the ribs also contribute by lifting the rib cage upwards and outwards.

When the volume of the thoracic cavity increases, the pressure within the lungs decreases. According to Boyle's Law, this causes air to flow from an area of higher pressure (the atmosphere) to an area of lower pressure (the lungs).

This is why the expanded lung volume results in air rushing in, completing the inspiration process.

Expiration

Expiration, or exhalation, is the process of releasing air from the lungs. This occurs when the diaphragm relaxes and moves back up into the thoracic cavity. At the same time, the intercostal muscles relax, causing the rib cage to move downwards.

With the volume of the thoracic cavity decreasing, the pressure within the lungs increases. As the pressure becomes greater than the atmospheric pressure, air is pushed out of the lungs.

This process helps expel carbon dioxide, a waste product of cellular metabolism, from the body.

Diaphragm Function

The diaphragm is a dome-shaped muscle located at the base of the lungs. Its primary function is to facilitate breathing by altering the volume of the thoracic cavity.

During inspiration, the diaphragm contracts and flattens, increasing the space in the thoracic cavity and allowing the lungs to expand. This results in a decrease in intrapulmonary pressure, drawing air into the lungs.

In contrast, during expiration, the diaphragm relaxes and returns to its dome shape. This decreases the thoracic cavity's volume, leading to an increase in pressure and forcing air out of the lungs.

Lung Volume

Lung volume refers to the different capacities and volumes of air that the lungs can hold. Various terms describe these volumes:

• Tidal Volume (TV): the amount of air inhaled or exhaled during a normal breath.
• Inspiratory Reserve Volume (IRV): the additional air that can be inhaled after a normal inhalation.
• Expiratory Reserve Volume (ERV): the additional air that can be exhaled after a normal exhalation.
• Residual Volume (RV): the air remaining in the lungs after a maximal exhalation.

These volumes play a crucial role in the mechanics of breathing, influencing how effectively air can be exchanged within the lungs.

Atmospheric Pressure

Atmospheric pressure plays a vital role in the mechanics of breathing. It is the force exerted by the weight of the air in the atmosphere. At sea level, this pressure is approximately 760 mmHg.

Air moves from areas of high pressure to areas of low pressure. During inspiration, when the pressure inside the lungs is lower than the atmospheric pressure, air flows into the lungs.

During expiration, when the pressure inside the lungs is higher than the atmospheric pressure, air is expelled from the lungs. This pressure gradient is essential for gas exchange during the respiratory cycle.