How does boyles law relate to inspiration and expiration

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See all questions in Gas Laws. The lungs themselves are passive during breathing, meaning they are not involved in creating the movement that helps inspiration and expiration. This is because of the adhesive nature of the pleural fluid, which allows the lungs to be pulled outward when the thoracic wall moves during inspiration.

The recoil of the thoracic wall during expiration causes compression of the lungs. Contraction and relaxation of the diaphragm and intercostals muscles found between the ribs cause most of the pressure changes that result in inspiration and expiration.

These muscle movements and subsequent pressure changes cause air to either rush in or be forced out of the lungs. Other characteristics of the lungs influence the effort that must be expended to ventilate.

Resistance is a force that slows motion, in this case, the flow of gases. The size of the airway is the primary factor affecting resistance. A small tubular diameter forces air through a smaller space, causing more collisions of air molecules with the walls of the airways. The following formula helps to describe the relationship between airway resistance and pressure changes:. As noted earlier, there is surface tension within the alveoli caused by water present in the lining of the alveoli. This surface tension tends to inhibit expansion of the alveoli.

However, pulmonary surfactant secreted by type II alveolar cells mixes with that water and helps reduce this surface tension. Without pulmonary surfactant, the alveoli would collapse during expiration.

Thoracic wall compliance is the ability of the thoracic wall to stretch while under pressure. This can also affect the effort expended in the process of breathing. In order for inspiration to occur, the thoracic cavity must expand. The expansion of the thoracic cavity directly influences the capacity of the lungs to expand.

If the tissues of the thoracic wall are not very compliant, it will be difficult to expand the thorax to increase the size of the lungs. Air flows down a pressure gradient, that is, air flows from an area of higher pressure to an area of lower pressure. It is this difference in pressures that drives pulmonary ventilation — the movement into and out of the lungs. Air flows into the lungs largely due to a difference in pressure; atmospheric pressure is greater than intra-alveolar pressure, and intra-alveolar pressure is greater than intrapleural pressure.

Air flows out of the lungs during expiration based on the same principle; pressure within the lungs becomes greater than the atmospheric pressure. In order to breathe, we manipulate the volume of our lungs in order to change their pressure. During inspiration , lung volume is increased by expanding our rib cage and moving the diaphragm downwards Figure 3.

This increased lung volume decreases lung pressure, resulting in air entering the lungs. During expiration , the process is reversed. Lung volume is decreased by recoiling the diaphragm to its original position and also the rib cage to its original smaller volume. This reduced lung volume increases lung pressure, resulting in air leaving the lungs Table 1.

A respiratory cycle is one sequence of inspiration and expiration. In general, two muscle groups are used during normal inspiration: the diaphragm and the external intercostal muscles. Additional muscles can be used if a bigger breath is required.

When the diaphragm contracts, it moves inferiorly toward the abdominal cavity, creating a larger thoracic cavity and more space for the lungs.

Contraction of the external intercostal muscles moves the ribs upward and outward, causing the rib cage to expand, which increases the volume of the thoracic cavity. Due to the adhesive force of the pleural fluid, the expansion of the thoracic cavity forces the lungs to stretch and expand as well. This increase in volume leads to a decrease in intra-alveolar pressure, creating a pressure lower than atmospheric pressure. As a result, a pressure gradient is created that drives air into the lungs.

Figure 3. Inspiration and expiration occur due to the expansion and contraction of the thoracic cavity, respectively. The process of normal expiration is passive, meaning that energy is not required to push air out of the lungs. Instead, the elasticity of the lung tissue causes the lung to recoil, as the diaphragm and intercostal muscles relax following inspiration.

In turn, the thoracic cavity and lungs decrease in volume, causing an increase in interpulmonary pressure. The interpulmonary pressure rises above atmospheric pressure, creating a pressure gradient that causes air to leave the lungs.

There are different types, or modes, of breathing that require a slightly different process to allow inspiration and expiration. Quiet breathing , also known as eupnea, is a mode of breathing that occurs at rest and does not require the cognitive thought of the individual.

During quiet breathing, the diaphragm and external intercostals must contract. A deep breath, called diaphragmatic breathing, requires the diaphragm to contract. As the diaphragm relaxes, air passively leaves the lungs. A shallow breath, called costal breathing, requires contraction of the intercostal muscles. As the intercostal muscles relax, air passively leaves the lungs.

In contrast, forced breathing , also known as hyperpnea, is a mode of breathing that can occur during exercise or actions that require the active manipulation of breathing, such as singing. During forced breathing, inspiration and expiration both occur due to muscle contractions. In addition to the contraction of the diaphragm and intercostal muscles, other accessory muscles must also contract.

During forced inspiration, muscles of the neck, including the scalenes, contract and lift the thoracic wall, increasing lung volume. During forced expiration, accessory muscles of the abdomen, including the obliques, contract, forcing abdominal organs upward against the diaphragm. This helps to push the diaphragm further into the thorax, pushing more air out.

In addition, accessory muscles primarily the internal intercostals help to compress the rib cage, which also reduces the volume of the thoracic cavity. Respiratory volume is the term used for various volumes of air moved by or associated with the lungs at a given point in the respiratory cycle.

There are four major types of respiratory volumes: tidal, residual, inspiratory reserve, and expiratory reserve Figure 4. Figure 4. These two graphs show a respiratory volumes and b the combination of volumes that results in respiratory capacity. Tidal volume TV is the amount of air that normally enters the lungs during quiet breathing, which is about milliliters. Expiratory reserve volume ERV is the amount of air you can forcefully exhale past a normal tidal expiration, up to milliliters for men.

Inspiratory reserve volume IRV is produced by a deep inhalation, past a tidal inspiration. This is the extra volume that can be brought into the lungs during a forced inspiration. Residual volume RV is the air left in the lungs if you exhale as much air as possible.

The residual volume makes breathing easier by preventing the alveoli from collapsing. Respiratory capacity is the combination of two or more selected volumes, which further describes the amount of air in the lungs during a given time. TLC is about mL air for men, and about mL for women. Vital capacity VC is the amount of air a person can move into or out of his or her lungs, and is the sum of all of the volumes except residual volume TV, ERV, and IRV , which is between and milliliters. Inspiratory capacity IC is the maximum amount of air that can be inhaled past a normal tidal expiration, is the sum of the tidal volume and inspiratory reserve volume.

On the other hand, the functional residual capacity FRC is the amount of air that remains in the lung after a normal tidal expiration; it is the sum of expiratory reserve volume and residual volume. Watch this video to learn more about lung volumes and spirometers. Explain how spirometry test results can be used to diagnose respiratory diseases or determine the effectiveness of disease treatment. In addition to the air that creates respiratory volumes, the respiratory system also contains anatomical dead space, which is air that is present in the airway that never reaches the alveoli and therefore never participates in gas exchange.

Alveolar dead space involves air found within alveoli that are unable to function, such as those affected by disease or abnormal blood flow. Total dead space is the anatomical dead space and alveolar dead space together, and represents all of the air in the respiratory system that is not being used in the gas exchange process.

Breathing usually occurs without thought, although at times you can consciously control it, such as when you swim under water, sing a song, or blow bubbles. The respiratory rate is the total number of breaths, or respiratory cycles, that occur each minute. Respiratory rate can be an important indicator of disease, as the rate may increase or decrease during an illness or in a disease condition.

The respiratory rate is controlled by the respiratory center located within the medulla oblongata in the brain, which responds primarily to changes in carbon dioxide, oxygen, and pH levels in the blood. The normal respiratory rate of a child decreases from birth to adolescence. A child under 1 year of age has a normal respiratory rate between 30 and 60 breaths per minute, but by the time a child is about 10 years old, the normal rate is closer to 18 to By adolescence, the normal respiratory rate is similar to that of adults, 12 to 18 breaths per minute.

The control of ventilation is a complex interplay of multiple regions in the brain that signal the muscles used in pulmonary ventilation to contract Table 3. The result is typically a rhythmic, consistent ventilation rate that provides the body with sufficient amounts of oxygen, while adequately removing carbon dioxide.

Inspiration occurs when the inspiratory muscles—that is, the diaphragm and the external intercostal muscles—contract. Contraction of the diaphragm the skeletal muscle below the lungs causes an increase in the size of the thoracic cavity, while contraction of the external intercostal muscles elevates the ribs and sternum. Thus, both muscles cause the lungs to expand, increasing the volume of their internal air passages.

In response, the air pressure inside the lungs decreases below that of air outside the body. Because gases move from regions of high pressure to low pressure, air rushes into the lungs. Expiration occurs when the diaphragm and external intercostal muscles relax.

In response, the elastic fibers in lung tissue cause the lungs to recoil to their original volume. The pressure of the air inside the lungs then increases above the air pressure outside the body, and air rushes out.

During high rates of ventilation, expiration is facilitated by contraction of the expiratory muscles the intercostal muscles and the abdominal muscles.