Which muscle aids expiration

The trachea is also lined with cilia, which sweep fluids and foreign particles out of the airway so that they stay out of the lungs.

At its bottom end, the trachea divides into left and right air tubes called bronchi pronounced: BRAHN-kye , which connect to the lungs. Within the lungs, the bronchi branch into smaller bronchi and even smaller tubes called bronchioles pronounced: BRAHN-kee-olz.

Bronchioles end in tiny air sacs called alveoli, where the exchange of oxygen and carbon dioxide actually takes place. Each person has hundreds of millions of alveoli in their lungs. This network of alveoli, bronchioles, and bronchi is known as the bronchial tree. The lungs also contain elastic tissues that allow them to inflate and deflate without losing shape. They're covered by a thin lining called the pleura pronounced: PLUR-uh. The chest cavity, or thorax pronounced: THOR-aks , is the airtight box that houses the bronchial tree, lungs, heart, and other structures.

The top and sides of the thorax are formed by the ribs and attached muscles, and the bottom is formed by a large muscle called the diaphragm pronounced: DYE-uh-fram.

The chest walls form a protective cage around the lungs and other contents of the chest cavity. The cells in our bodies need oxygen to stay alive. Carbon dioxide is made in our bodies as cells do their jobs.

The lungs and respiratory system allow oxygen in the air to be taken into the body, while also letting the body get rid of carbon dioxide in the air breathed out. The net effect is that the cycle of compression and relaxation propels the blood in the direction of the heart. Venous valves prevent the blood from flowing backwards, thereby permitting unidirectional flow that enhances venous return. When a person is standing, postural muscles in the legs alternately contract and relax to keep the body in balance.

This muscle activity promotes venous return and helps to maintain central venous pressure and venous return, and to lower venous and capillary pressures in the feet and lower limbs. Respiratory activity influences venous return to the heart. Briefly, increasing the rate and depth of respiration promotes venous return and therefore enhances cardiac output.

Non-typical respiratory activity such as being on positive pressure ventilation or doing a forced expiration against a closed glottis Valsalva maneuver impedes and therefore reduces venous return and cardiac output.

Respiratory activity affects venous return through changes in right atrial pressure, which is an important component of the pressure gradient for venous return. Increasing right atrial pressure impedes venous return, while lowering this pressure facilitates venous return. Respiratory activity can also affect the diameter of the thoracic vena cava and cardiac chambers, which either directly e.

Pressures in the right atrium and thoracic vena cava are very dependent on intrapleural pressure P pl , which is the pressure within the thoracic space between the organs lungs, heart, vena cava and the chest wall.

This directionality of airflow requires two cycles of air intake and exhalation to completely remove the air from the lungs. Avian respiratory system : a Birds have a flow-through respiratory system in which air flows unidirectionally from the posterior sacs into the lungs, then into the anterior air sacs. The air sacs connect to openings in hollow bones. Breathing includes several components, including flow-resistive and elastic work; surfactant production; and lung resistance and compliance.

Explain the roles played by surfactant, flow-resistive and elastic work, and lung resistance and compliance in breathing. The respiratory rate contributes to the alveolar ventilation, or how much air moves into and out of the alveoli, which prevents carbon dioxide buildup in the alveoli. There are two ways to keep the alveolar ventilation constant: increase the respiratory rate while decreasing the tidal volume of air per breath shallow breathing , or decrease the respiratory rate while increasing the tidal volume per breath.

In either case, the ventilation remains the same, but the work done and type of work needed are quite different. Both tidal volume and respiratory rate are closely regulated when oxygen demand increases. There are two types of work conducted during respiration: flow-resistive and elastic work.

Flow-resistive work refers to the work of the alveoli and tissues in the lung, whereas elastic work refers to the work of the intercostal muscles, chest wall, and diaphragm.

When the respiratory rate is increased, the flow-resistive work of the airways is increased and the elastic work of the muscles is decreased. When the respiratory rate is decreased, the flow-resistive work is decreased and the elastic work is increased. Surfactant is a complex mixture of phospholipids and lipoproteins that works to reduce the surface tension that exists between the alveoli tissue and the air found within the alveoli.

By lowering the surface tension of the alveolar fluid, it reduces the tendency of alveoli to collapse. Surfactant works like a detergent to reduce the surface tension, allowing for easier inflation of the airways. When a balloon is first inflated, it takes a large amount of effort to stretch the plastic and start to inflate the balloon.

If a little bit of detergent were applied to the interior of the balloon, then the amount of effort or work needed to begin to inflate the balloon would decrease; it would become much easier.

This same principle applies to the airways. A small amount of surfactant on the airway tissues reduces the effort or work needed to inflate those airways and is also important for preventing collapse of small alveoli relative to large alveoli.

Sometimes, in babies that are born prematurely, there is lack of surfactant production; as a result, they suffer from respiratory distress syndrome and require more effort to inflate the lungs.

In pulmonary diseases, the rate of gas exchange into and out of the lungs is reduced. Two main causes of decreased gas exchange are compliance how elastic the lung is and resistance how much obstruction exists in the airways. A change in either can dramatically alter breathing and the ability to take in oxygen and release carbon dioxide.

Examples of restrictive diseases are respiratory distress syndrome and pulmonary fibrosis. In both diseases, the airways are less compliant and stiff or fibrotic, resulting in a decrease in compliance because the lung tissue cannot bend and move. In these types of restrictive diseases, the intrapleural pressure is more positive and the airways collapse upon exhalation, which traps air in the lungs.

Forced or functional vital capacity FVC , which is the amount of air that can be forcibly exhaled after taking the deepest breath possible, is much lower than in normal patients; the time it takes to exhale most of the air is greatly prolonged.

A patient suffering from these diseases cannot exhale the normal amount of air. Obstructive diseases and conditions include emphysema, asthma, and pulmonary edema. In emphysema, which mostly arises from smoking tobacco, the walls of the alveoli are destroyed, decreasing the surface area for gas exchange. The overall compliance of the lungs is increased, because as the alveolar walls are damaged, lung elastic recoil decreases due to a loss of elastic fibers; more air is trapped in the lungs at the end of exhalation.

Asthma is a disease in which inflammation is triggered by environmental factors, obstructing the airways. The obstruction may be due to edema, smooth muscle spasms in the walls of the bronchioles, increased mucus secretion, damage to the epithelia of the airways, or a combination of these events.

Those with asthma or edema experience increased occlusion from increased inflammation of the airways. This tends to block the airways, preventing the proper movement of gases. Those with obstructive diseases have large volumes of air trapped after exhalation. They breathe at a very high lung volume to compensate for the lack of airway recruitment. The pulmonary circulation pressure is very low compared to that of the systemic circulation; it is also independent of cardiac output.

Recruitment is the process of opening airways that normally remain closed when cardiac output increases. As cardiac output increases, the number of capillaries and arteries that are perfused filled with blood increases. These capillaries and arteries are not always in use, but are ready if needed. However, at times, there is a mismatch between the amount of air ventilation, V and the amount of blood perfusion, Q in the lungs.

Dead space is characterized by regions of broken down or blocked lung tissue. Dead spaces can severely impact breathing due to the reduction in surface area available for gas diffusion. As a result, the amount of oxygen in the blood decreases, whereas the carbon dioxide level increases.

Anatomical dead space, or anatomical shunt, arises from an anatomical failure, while physiological dead space, or physiological shunt, arises from a functional impairment of the lung or arteries. An example of an anatomical shunt is the effect of gravity on the lungs. The lung is particularly susceptible to changes in the magnitude and direction of gravitational forces.

When someone is standing or sitting upright, the pleural pressure gradient leads to increased ventilation further down in the lung.

As a result, the intrapleural pressure is more negative at the base of the lung than at the top; more air fills the bottom of the lung than the top. Likewise, it takes less energy to pump blood to the bottom of the lung than to the top when in a prone position lying down.