Mechanics of breathing I Flashcards
How do changes in lung volume contribute to helping air move from the atmosphere to the alveoli?
Changes in lung volume induces changes in alveolar pressure, which generates pressure gradients between alveoli & atmosphere, causing air to flow.
How does the lung volume change during inspiration and how does this help air flow from the atmosphere to the alveoli?
During inspiration the diaphragm contracts & thoracic cavity expands (lung volume increases).
This causes the Alveolar pressure to decrease meaning alveolar pressure is now lower than atmospheric.
This creates a pressure gradient between the alveoli and the atmosphere which the air moves down to move into the alveoli.
How does the lung volume change during expiration and how does this help air flow from the alveoli back out to the atmosphere?
During expiration the diaphragm relaxes & the lungs recoil causing lung volume decreases.
This causes the Alveolar pressure to increase meaning alveolar pressure is now higher than atmospheric.
This creates a pressure gradient between the alveoli and the atmosphere which the air moves down to go back out into the atmosphere.
Between inspiration and expiration why is there no movement of air?
The alveolar pressure and atmospheric pressure are equal meaning there is no pressure gradient for the air to move down.
What is the pleural cavity?
Fluid filled space between the 2 membranes (pleura) that line the chest wall and each lung.
What are the 2 pleura that surround the lungs?
Visceral (inner) pleura - attached to lungs
Parietal (outer) pleura - attached to chest wall
What are the functions of the pleural cavity?
Helps to provide a frictionless surface to aid movement of the lungs.
Also, ensures that movement of the chest wall results in movement of the lungs since lungs aren’t directly connected to chest wall.
Both the chest wall and the lungs have elasticity and are able to recoil. How does their ability to recoil affect the pressure within the pleural cavity?
The opposing elastic recoil of the chest wall (outward) and lungs (inward) causes the pleural cavity to be stretched slightly thus increasing the volume within pleural cavity. Because pleural cavity is sealed increase in volume decreases pressure leading to generation of negative pressure.
What is negative pressure?
Lower number of molecules within a certain volume relative to the surroundings. This generates a collapsing force (pulls surfaces of contained space together) which decreases the volume and works to re-establish equilibrium between the sealed space and the surroundings.
What is positive pressure?
Higher number of molecules within a certain volume relative to the surroundings. This generates an expanding force (pushes surfaces of contained space apart) which increases the volume and works to re-establish equilibrium between the sealed space and the surroundings.
What are the 2 opposing forces that causes the 2 pleura to move in different directions?
Lung recoil - force pulling the visceral pleura inwards
Negative intrapleural pressure - force pulling the visceral pleura outwards
How do changes in the forces acting on the pleura result in an increase in lung volume during inspiration?
During inspiration, muscular contraction pulls the parietal pleura outwards, stretching the chest cavity. This causes an increase in volume and decrease in intrapleural pressure.
The decreased (more negative) intrapleural pressure creates a greater level of force acting to pull the pleurae together (effectively acting to pull the visceral pleura outwards).
When the force generated by negative intrapleural pressure becomes greater than the inward force generated by lung recoil, the visceral pleura (and the lungs) will be pulled outwards, expanding the lung.
How do changes in the forces acting on the pleura result in an decrease in lung volume during passive expiration?
During (passive) expiration, relaxation of previously contracted respiratory muscles, reduces the outward force acting on the parietal pleura, reducing the degree to which the cavity is stretched, increasing the negative intrapleural pressure
When the increased (less negative) intrapleural pressure no longer generates sufficient force to overcome the elastic recoil of the lung, the visceral pleura will be pulled inward (along with the pleural cavity and parietal pleura) decreasing lung volume.
Why is the decrease in lung volume during forced expiration much quicker than during passive expiration?
During a forced expiration, contraction of other respiratory muscles (such as the abdominals and internal intercostals) acts to provide further inward force on the parietal pleura, compressing the pleural cavity (further increasing intrapleural pressure), forcing an increased and more rapid decline in lung volume.
Briefly describe the processes that leads to air being moved into the alveoli during inspiration?
Respiratory muscles (e.g. diaphragm) contract
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Parietal pleura pulled outwards
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Volume of thoracic cavity increases
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Intrapleural pressure becomes more negative
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Outward force exerted on visceral pleura becomes greater than inward force of lung recoil
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Visceral pleura pulled outwards, Lungs expand, increasing volume
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PAlv (alveolar pressure) decreases below PAtm (atmospheric pressure) creating pressure gradient
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Air moves down pressure gradient, through airways into alveoli, expanding the lungs
