Mechanics of Breathing I Flashcards
what is the primary function of the respiratory system?
to ventilate gas exchange surfaces by moving air (a mixture of gases) between the alveoli and the atmosphere via the airways.
what type of gradient do gases naturally move down?
a pressure gradient
-gases naturally move from areas of higher pressure to lower pressure, until an equilibrium is re-established
The total volume of air that an individual can move in/out of the lungs during inspiration/expiration is important to what?
important to the quantity of oxygen that reaches alveolar surfaces
name some factors that cause total lung volumes to vary between individuals?
- height
- sex
- age
- the extent of specific respiratory diseases.
the ideal gas law
PV=nRT
pressure x volume = number of moles x gas constant x temperature
pressure in kPa
volume in Litres
Temperature in Kelvins
boyle’s law
Pressure = the number of gas molecules ‘n’ within a given volume
If ‘n’ remains constant, ↑ Volume = ↓ Pressure
essentially how does the respiratory system like to move gases?
manipulate the space they’re in in order to move them
what is quiet breathing?
breathing at rest
changes in lung volume induce changes in what?
changes in lung volume induce changes in alveolar pressure
-this generates pressure gradients between alveoli & atmosphere, causing air to flow
if you want air to come from the atmosphere into the lungs where does the pressure have to be higher?
If you want air to come from atmosphere into the lungs the pressure in the atmosphere has to be higher than that in the lungs, so it will travel down a pressure gradient into the lungs
how do you create the pressure gradient?
in order to create the gradient, the pressure of the gas in the atmosphere or the pressure of the gas in the lungs must be changed:
- given you can’t control the pressure in the atmosphere, its only the volume and pressure of the lungs that can be controlled
- the pressure in the lungs is manipulated relative to the atmosphere in order to get a pressure gradient both ways.
what is the main respiratory muscle involved in passive/relaxed breathing?
the diaphragm
what happens in inspiration?
-the outer surfaces of the lung are pulled outwards (expansion)
the diaphragm contracts
-thoracic cavity expands, increasing volume
-alveolar pressure decreases
-air enters down a pressure gradient, from high (atmosphere) to low (alveoli) pressure
what happens in expiration?
-air within the lung is compressed diaphragm relaxes and lung recoils -thoracic cavity volume decreases -alveolar pressure increases (becomes higher than pressure in atmosphere) -air leaves down a pressure gradient
at the end of expiration why is there no movement of air?
because at the end of expiration, the pressure in the alveoli = the pressure in the atmosphere
what structure indirectly attaches the lungs and chest wall?
the pleural cavity
what is the pleural cavity?
fluid filled space between the membranes (pleura) that line the chest wall and each lung
what is the role of the pleura?
- reduce friction between the lungs and the chest wall during breathing
- ensures that movements of the chest wall result in movements of the lungs, so when the chest wall expands, the lungs also expand.
when there is a change is pressure how is equilibrium re-established?
1) either movement of liquid/gas
2) collapse/expansion of volume (at the expense of surrounding structures)
what is negative pressure?
when there is a lower number of molecules per volume (relative to surroundings)
→ generates collapsing force (pulls surfaces of contained space together)
how is negative pressure generated in the body?
The opposing elastic recoil of the chest wall (wants to recoil outwards) and lungs (wants to recoil inwards) generates negative pressure within the pleural cavity (sealed cavity + increased volume = decreased pressure).
what is the aim of negative pressure?
Negative pressure acts to pull the two membranes together (more negative pressure = more force pulling pleurae together)
what are the names of the 2 pleura?
- visceral pleura, closest to lungs
- parietal pleura (a serous membrane), closest to chest wall
what is positive pressure?
-increased number of molecules per volume (relative to surroundings)
→ generates expanding force (pushes surfaces of contained space apart)
explain the effect of negative pressure:
- pleural pressure decreases, means its slightly unstable and the structures want to collapse in
- so, lung volume increases because the pleural membranes have essentially collapsed and in order to do that it has pulled the lungs open. Increase in volume means decrease in pressure, so air comes in.
explain the effect of positive pressure?
- increase pressure in the pleural space so that it’s greater than the lungs, by compressing it slightly.
- the increase in pressure means it wants to exert an expanding force that pushes the 2 membranes apart, decreasing lung volume
what is the expansion and retraction of the lung determined by?
the relative size of opposing forces
when the will lung volume remain constant?
when the force pulling the visceral pleura inwards (lung recoil) = the force pulling the visceral pleura outwards (negative intrapleural pressure)
what directions do the lungs and chest cavity have a tendency to move in?
- On the inside, the lung has elastic qualities- want to coil inwards
- On the outside, the chest cavity wants to extend outwards
what qualities do the lungs have that make them want to coil inwards?
elastic qualities (elastic recoil)
during inspiration, what does muscular contraction do?
muscular contraction pulls the parietal pleura outwards, stretching the cavity, decreasing interpleural pressure (making it more negative)
what does the decrease in intrapleural pressure create?
the decreased intrapleural pressure creates a greater level of force acting to pull the pleura together
during inspiration, why is the visceral pleura pulled outwards, expanding the lungs?
the visceral pleura is pulled outwards when the force generated by negative intrapleural pressure becomes greater then the inward force generated by lung recoil
during expiration, what does relaxation of respiratory muscles do?
reduces the outward force acting on the parietal pleura, reducing the degree to which the cavity is stretched, increasing intrapelural pressure
what happens when the intrapleural pressure increases so much that it no longer generates sufficient force to overcome the elastic recoil of the lung?
the visceral pleura will be pulled inwards (along with the pleural cavity and parietal pleura), decreasing lung volume
what happens in a forced expiration, what is the role of contraction of other respiratory muscles?
- contraction of other respiratory muscles (abdominals, internal intercostals) provide further inward pressure on the parietal pleura
- this compresses the pleural cavity, further increasing intrapleural pressure
- forcing an increased and more rapid decline in lung volume
changing the volume of the thoracic cavity causes what?
Movement of air into/out of the lungs
what does expiration involve?
- elastic recoil of the lungs
- relaxation of respiratory muscles
does compression of the lungs due to increased intrapleural pressure occur in both forced expiration and quiet breathing?
NO, compression of the lungs only occurs during forced expiration
summary of inspiration:
Respiratory muscles (e.g. diaphragm) contract
↓
Volume of thoracic cavity increases
↓
Intrapleural pressure becomes more negative
↓
Outward force exerted on visceral pleura becomes greater than inward recoil force
↓
Lungs expand, increasing volume
↓
PAlv (alveolar pressure) decreases below PAtm (atmospheric pressure)
↓
Air moves down pressure gradient, through airways into alveoli, expanding the lungs
summary of expiration:
Respiratory muscles (e.g. diaphragm) relax, lungs recoil due to elastic fibres ↓ Volume of thoracic cavity decreases ↓ Intrapleural pressure increases ↓ Lungs compressed*, volume decreases ↓ PAlv increases above PAtm ↓ Air moves down pressure gradient, into atmosphere, deflating lungs
what is the speed of airflow is dependent on?
the pressure gradient and the level of airway resistance present.
give an example of when the negative intrapleural pressure is lost?
an open pneumothorax
what happens in an open pneumothorax?
- in one of the pleural membranes (e.g. a stab wound), air will enter the pleural cavity (down its pressure gradient) equalising intrapleural pressure with the atmosphere.
- no longer any negative interpleural pressure pulling the lungs towards the chest wall
- the entry of air causes an increase in pleural cavity volume, reducing intrapleural pressure generated during inspiration, preventing lungs from expanding properly
- as a result, the lungs can recoil to a low volume-lung collapse.
what is a closed pneumothorax?
Closed is whenair getsin thepleural space without any outside wound- sometimes happens when the lung is already injured somehow eg. from diseases such as cancer or cystic fibrosis
so what does a pneumothorax involve?
involves an entry of air into the pleural cavity, loss of negative intrapleural pressure, and collapse of lung tissue
what does a pneumothorax cause?
Pneumothorax causes affected parts of the lung to collapse due to elastic recoil
In a healthy respiratory system, the visceral and parietal pleura (effectively the lungs and chest wall) are prevented from separating by what?
prevented from separating by the existence of negative pressure within the pleural cavity.
what issues will a collapsed lung create?
-ability to breathe and ventilate gas exchange structures sufficiently in alveoli
