Anything that increases the number of collisions for example, a rise in temperature increases the speed at which molecules travel will cause a rise in gas pressure and vice versa. During a breathing cycle, air moves in and out of the lungs by bulk flow. The respiratory muscles are responsible for the changes in the shape and volume of the chest cavity that cause the air movements in breathing.
Inspiration or inhalation is an active process that occurs when the chest cavity enlarges because of the contraction of the muscles.
The dome-shaped diaphragm is the most important muscle at this stage. At the start of inspiration, the diaphragm contracts and flattens, pressing down on the abdominal contents and lifting the ribcage. This increases the vertical height of the thoracic cavity Fig 1. At the same time, the external intercostal muscles between the ribs contract and lift the ribcage and pull the sternum forward, thus increasing the front-to-back and side-to-side dimensions Figs The outer parietal layer of the pleura is attached to the diaphragm and the inside of the chest wall, and so moves with those structures.
As a result, the inner visceral layer of the pleura, which is attached to the surface of the lungs, follows and the lungs expand, that is their volume increases. The air in the lungs now has a larger space to fill and so its pressure falls.
This produces a partial vacuum, which sucks air into the lungs by bulk flow. Air continues to move into the lungs until the intrapulmonary pressure is the same as atmospheric pressure. The chemoreceptors are only able to sense dissolved oxygen molecules, not the oxygen that is bound to hemoglobin.
As you recall, the majority of oxygen is bound by hemoglobin; when dissolved levels of oxygen drop, hemoglobin releases oxygen. Therefore, a large drop in oxygen levels is required to stimulate the chemoreceptors of the aortic arch and carotid arteries. The hypothalamus and other brain regions associated with the limbic system also play roles in influencing the regulation of breathing by interacting with the respiratory centers.
The hypothalamus and other regions associated with the limbic system are involved in regulating respiration in response to emotions, pain, and temperature. For example, an increase in body temperature causes an increase in respiratory rate. Feeling excited or the fight-or-flight response will also result in an increase in respiratory rate. Sleep apnea is a chronic disorder that can occur in children or adults, and is characterized by the cessation of breathing during sleep.
These episodes may last for several seconds or several minutes, and may differ in the frequency with which they are experienced. Sleep apnea leads to poor sleep, which is reflected in the symptoms of fatigue, evening napping, irritability, memory problems, and morning headaches. In addition, many individuals with sleep apnea experience a dry throat in the morning after waking from sleep, which may be due to excessive snoring. There are two types of sleep apnea: obstructive sleep apnea and central sleep apnea.
Obstructive sleep apnea is caused by an obstruction of the airway during sleep, which can occur at different points in the airway, depending on the underlying cause of the obstruction. For example, the tongue and throat muscles of some individuals with obstructive sleep apnea may relax excessively, causing the muscles to push into the airway. Another example is obesity, which is a known risk factor for sleep apnea, as excess adipose tissue in the neck region can push the soft tissues towards the lumen of the airway, causing the trachea to narrow.
In central sleep apnea, the respiratory centers of the brain do not respond properly to rising carbon dioxide levels and therefore do not stimulate the contraction of the diaphragm and intercostal muscles regularly.
As a result, inspiration does not occur and breathing stops for a short period. In some cases, the cause of central sleep apnea is unknown. However, some medical conditions, such as stroke and congestive heart failure, may cause damage to the pons or medulla oblongata.
In addition, some pharmacologic agents, such as morphine, can affect the respiratory centers, causing a decrease in the respiratory rate. The symptoms of central sleep apnea are similar to those of obstructive sleep apnea.
A diagnosis of sleep apnea is usually done during a sleep study, where the patient is monitored in a sleep laboratory for several nights. Treatment of sleep apnea commonly includes the use of a device called a continuous positive airway pressure CPAP machine during sleep.
The CPAP machine has a mask that covers the nose, or the nose and mouth, and forces air into the airway at regular intervals. This pressurized air can help to gently force the airway to remain open, allowing more normal ventilation to occur. Other treatments include lifestyle changes to decrease weight, eliminate alcohol and other sleep apnea—promoting drugs, and changes in sleep position.
In addition to these treatments, patients with central sleep apnea may need supplemental oxygen during sleep. Pulmonary ventilation is the process of breathing, which is driven by pressure differences between the lungs and the atmosphere.
Atmospheric pressure is the force exerted by gases present in the atmosphere. The force exerted by gases within the alveoli is called intra-alveolar intrapulmonary pressure, whereas the force exerted by gases in the pleural cavity is called intrapleural pressure. Typically, intrapleural pressure is lower, or negative to, intra-alveolar pressure. The difference in pressure between intrapleural and intra-alveolar pressures is called transpulmonary pressure. In addition, intra-alveolar pressure will equalize with the atmospheric pressure.
Pressure is determined by the volume of the space occupied by a gas and is influenced by resistance. Air flows when a pressure gradient is created, from a space of higher pressure to a space of lower pressure.
A gas is at lower pressure in a larger volume because the gas molecules have more space to in which to move. The same quantity of gas in a smaller volume results in gas molecules crowding together, producing increased pressure. Resistance is created by inelastic surfaces, as well as the diameter of the airways. Resistance reduces the flow of gases. The surface tension of the alveoli also influences pressure, as it opposes the expansion of the alveoli. However, pulmonary surfactant helps to reduce the surface tension so that the alveoli do not collapse during expiration.
The ability of the lungs to stretch, called lung compliance, also plays a role in gas flow. The more the lungs can stretch, the greater the potential volume of the lungs. The greater the volume of the lungs, the lower the air pressure within the lungs. Pulmonary ventilation consists of the process of inspiration or inhalation , where air enters the lungs, and expiration or exhalation , where air leaves the lungs.
During inspiration, the diaphragm and external intercostal muscles contract, causing the rib cage to expand and move outward, and expanding the thoracic cavity and lung volume. This creates a lower pressure within the lung than that of the atmosphere, causing air to be drawn into the lungs.
During expiration, the diaphragm and intercostals relax, causing the thorax and lungs to recoil. The air pressure within the lungs increases to above the pressure of the atmosphere, causing air to be forced out of the lungs.
However, during forced exhalation, the internal intercostals and abdominal muscles may be involved in forcing air out of the lungs. Respiratory volume describes the amount of air in a given space within the lungs, or which can be moved by the lung, and is dependent on a variety of factors. Tidal volume refers to the amount of air that enters the lungs during quiet breathing, whereas inspiratory reserve volume is the amount of air that enters the lungs when a person inhales past the tidal volume.
Expiratory reserve volume is the extra amount of air that can leave with forceful expiration, following tidal expiration. Residual volume is the amount of air that is left in the lungs after expelling the expiratory reserve volume.
Respiratory capacity is the combination of two or more volumes. Anatomical dead space refers to the air within the respiratory structures that never participates in gas exchange, because it does not reach functional alveoli. Respiratory rate is the number of breaths taken per minute, which may change during certain diseases or conditions. Both respiratory rate and depth are controlled by the respiratory centers of the brain, which are stimulated by factors such as chemical and pH changes in the blood.
These changes are sensed by central chemoreceptors, which are located in the brain, and peripheral chemoreceptors, which are located in the aortic arch and carotid arteries. A rise in carbon dioxide or a decline in oxygen levels in the blood stimulates an increase in respiratory rate and depth. As the diaphragm relaxes, it moves superiorly. During expiration, the diaphragm and intercostals relax, causing the thorax and lungs to recoil.
Tidal volume refers to the amount of air that enters the lungs during quiet breathing, whereas inspiratory reserve volume is the amount of air that enters the lungs when a person inhales past the tidal volume. The muscles that contribute to quiet breathing are the external intercostal muscles and the diaphragm.
The external and internal intercostals are the muscles that fill the gaps between the ribs. When drawing breath i. The extra thoracic component narrows during inspiration and widens during expiration. The intrathoracic component narrows during expiration and widens during inspiration. If there is obstruction it gets worse during the phase of inspiration, when the airway size is smaller.
This type of muscle only exists in your heart. Unlike other types of muscle, cardiac muscle never gets tired. It works automatically and constantly without ever pausing to rest.
Cardiac muscle contracts to squeeze blood out of your heart, and relaxes to fill your heart with blood. What Are the Symptoms of Chronic Bronchitis?
Cough is the most common symptom of chronic bronchitis. The cough may be dry or it may produce phlegm. Significant phlegm production suggests that the lower respiratory tract and the lung itself may be infected, symptoms which may also be concerning for pneumonia. Which muscles are activated during forced expiration? During forced expiration, the internal intercostal muscles and the oblique, and transversus abdominal muscles contract to increase the intra-abdominal pressure and depress the rib cage.
In healthy people quiet expiration or exhalation is passive and relies on elastic recoil of the stretched lungs as the inspiratory muscles relax, rather than on muscle contraction. 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. The main difference between inspiration and expiration is that inspiration inhalation is the process of taking air into the lungs whereas expiration exhalation is the process of liberating air from the lungs. Inspiration and expiration are the two phases of the process of breathing.
Expiration, also called exhalation, is the flow of the respiratory current out of the organism. The purpose of exhalation is to remove metabolic waste, primarily carbon dioxide from the body from gas exchange.
The pathway for exhalation is the movement of air out of the conducting zone, to the external environment during breathing. Respiratory System: As the diaphragm relaxes, the pleural cavity contracts, which exerts pressure on the lungs, which reduces the volume of the lungs as air is passively pushed out of the lungs.
Expiration is typically a passive process that happens from the relaxation of the diaphragm muscle that contracted during inspiration. The primary reason that expiration is passive is due to the elastic recoil of the lungs. The elasticity of the lungs is due to molecules called elastins in the extracellular matrix of lung tissues and is maintained by surfactant, a chemical that prevents the elasticity of the lungs from becoming too great by reducing surface tension from water.
Without surfactant the lungs would collapse at the end of expiration, making it much more difficult to inhale again. Because the lung is elastic, it will automatically return to its smaller size as air leaves the lung. Exhalation begins when inhalation ends. An increase in pressure leads to a decrease in volume inside the lung, and air is pushed out into the airways as the lung returns to its smaller size.
While expiration is generally a passive process, it can also be an active and forced process. There are two groups of muscles that are involved in forced exhalation. This happens due to elastic properties of the lungs, as well as the internal intercostal muscles that lower the rib cage and decrease thoracic volume.
As the thoracic diaphragm relaxes during exhalation it causes the tissue it has depressed to rise superiorly and put pressure on the lungs to expel the air. Expiration can be either voluntary or involuntary in order to serve different purposes for the body. These two types of expiration are controlled by different centers within the body.
Voluntary expiration is actively controlled. It is generally defined by holding air in the lungs and releasing it at a fixed rate, which enables control over when and how much air to exhale. Involuntary expiration is not under conscious control, and is an important component for metabolic function. Examples include breathing during sleep or meditation. Changes in breathing patterns may also occur for metabolic reasons, such as through increased breathing rate in people with acidosis from negative feedback.
The principle neural control center for involuntary expiration consists of the medulla oblongata and the pons, which are located in the brainstem directly beneath the brain. While these two structures are involved in neural respiratory control, they also have other metabolic regulatory functions for other body systems, such as the cardiovascular system.
Breathing patterns refer to the respiratory rate, which is defined as the frequency of breaths over a period of time, as well as the amount of air cycled during breathing tidal volume. Breathing patterns are an important diagnostic criteria for many diseases, including some which involve more than the respiratory system itself.
The respiratory rate is frequency of breaths over time. The time period is variable, but usually expressed in breaths per minute because it that time period allows for estimation of minute ventilation.
During normal breathing, the volume of air cycled through inhalation and exhalation is called tidal volume VT , and is the amount of air exchanged in a single breath.
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