Mechanics Of Breathing

Question 1

How does the respiratory system achieve movement

Answer 1

The respiratory system achieves movement of air by relying on the property of gas that means it
moves from areas of high pressure to low pressure. This will occur until an equilibrium is established.

Question 2

What does the manipulation of volume of gases cause

Answer 2

Manipulating the volume which gases occupy manipulates pressure and therefore the movement of
gas.

Question 3

How is changes in alveolar pressure induced

Answer 3

The respiratory system in fact utilises this property of gases by changing lung volume to induce
changes in alveolar pressure.

Question 4

Describe what happens during inspiration

Answer 4

During inspiration, the diaphragm contracts and the thoracic cavity
expands. This decreases pressure in the lungs below atmospheric pressure and this causes air to
move into the lungs.

Question 5

Describe what happens during expiration

Answer 5

During expiration, the diaphragm relaxes and the lung recoils. This decreases
the thoracic cavity volume increasing alveolar pressure and therefore inducing the movement of air
out of the lungs.

Question 6

What is a passive process expiration or inspiration

Answer 6

The fact that the diaphragm contracts during inspiration and relaxes during
expiration means that inspiration is an active process at rest whilst expiration is a passive process at
rest.

Question 7

What is a factor that complicates breathing

Answer 7

A factor that complicates breathing is the fact the lungs and chest (where the muscles that move the
lungs are located) are not directly connected.

Question 8

What connects the lungs and chest

Answer 8

It is in fact the pleural cavity that indirectly connects

them. Each lung and the chest are all surrounded by membranes known as pleurae.

Question 9

What lines the lungs and chest

Answer 9

The lungs are
lined by the visceral pleura and the chest is lined by the parietal pleura (surrounds the chest,
diaphragm and mediastinum).

Question 10

What is the fluid filled space between the two membranes called

Answer 10

The fluid filled space in between these two membranes is known as
the pleural cavity.

Question 11

What are the roles and functions of the pleural cavity

Answer 11

One of the roles of the pleural cavity is to provide a frictionless surface to aid the
movement of lungs during breathing. It also has the function of ensuring that the lungs move when
the chest wall moves (when the chest wall expands, so does the lungs and vice versa).

Question 12

How is a negative pressure in the pleural cavity formed

Answer 12

Both the lungs
and the chest both have elastic recoil properties in them in opposite directions. The chest wall recoil
outwards whilst the lung recoil inwards. This generates a negative pressure in the pleural cavity as it
is stretched slightly.

Question 13

Why is pleural cavity stretch minimal

Answer 13

However, since the cavity is filled with fluid (fluid resists stretching more than
gas), this stretching effect is minimal.

Question 14

How is a negative pressure in the lungs formed by the pleural cavity

Answer 14

The negative pressure is generated by this stretching effect as
well as the fact the cavity is sealed. The result is an increase in volume with the same number
amount of molecules. The effect of the negative pressure is that the two membranes are pulled
together as a collapsing force is generated.

Question 15

What does a positive pressure cause

Answer 15

A positive pressure on the other hand generates an
expanding force. The degree of the force produced in both cases relies on the degree of the negative
or positive pressure.

Question 16

What is the effect of positive and negative pressure pleural cavity

Answer 16

The effects of negative and positive pressure in the pleural cavity is that since
the pleural cavity pressure won’t change, the lung compensates for this by changing its volume.

Question 17

What happens if there is a negative pleural pressure

Answer 17

If
there is negative pressure, the lungs expand to compensate whilst if the pressure is positive, the
lungs will collapse.

Question 18

What happens when the lung volume changes

Answer 18

The change in lung volume draws air into or out of the lung depending on the
lung volume due to the changes in the air pressure of the lungs.
The expansion and retraction of the lung is determined by the relative size of opposing forces.

Question 19

What force acts inwards in the lungs

Answer 19

On the

inside, there is a force inwards caused by lung recoil.

Question 20

What aid the the outward recoil of lungs

Answer 20

On the outside, the chest wall wants to recoil
outwards. Muscle contractions (e.g. diaphragm), exerts further force outwards. In the pleural cavity,
there is an inward force generated by the negative pressure that pulls the membrane together. At the
point when the forces in the lung are at equilibrium, the volume of the lung does not change. If the
lung is expanding, the forces in the chest wall are greater than the forces generated by lung recoil
and vice versa.

Question 21

What happens to the parietal pleura during inspiration

Answer 21

During inspiration, muscular contraction pulls the parietal pleura outwards stretching
the pleural cavity slightly and decreasing the pressure in it. This increases the force that acts to pull
the two pleurae together. Since the parietal pleura is being pulled outwards already however, the
effective result of this increased force acting to pull the pleura together pulls the visceral pleura
outwards. This occurs when the force acting to pull the pleura together overcomes the force
generated by lung recoil. The lung will expand as the visceral pleura moves outwards.

Question 22

What happens to the parietal pleura during expiration

Answer 22

During expiration, the reverse situation occurs. The contracting muscles that pull the parietal pleura
relax reducing the force acting outwards. This reduces the degree to which the pleural cavity is
stretched outwards and the negative pressure in the pleural cavity now becomes more positive. When the intrapleural pressure no longer generates sufficient force to overcome elastic recoil of the
lung, the visceral pleura will be pulled inward, pulling the pleural cavity and parietal pleura inward with it and lung volume decreases.

Question 23

What happens during forced expiration

Answer 23

During forced expiration, contraction of other respiratory muscles
(including the abdominals and internal intercostal muscles) act to provide further inward force on
the parietal pleura compressing the pleural cavity further increasing interpleural pressure. This forces
an increase and more rapid decline of lung volume.

Question 24

What happens at the beginning of inspiration

Answer 24

At the beginning of inspiration, respiratory muscles contract to increase the volume of the thoracic
cavity. This causes a decrease in the intrapleural pressure that results in the outward force exerted on
the pleural membrane to be greater than inward recoil force. This causes the lungs to expand and
increase in volume.

Question 25

What happens when lungs expand and increase in volume

Answer 25

Alveolar pressure therefore decreases as a result to below atmospheric pressure
and air moves into the lungs down the pressure gradient.

Question 26

What happens at the beginning of expiration and forced

Answer 26

During expiration, the respiratory muscles
relax and the lungs recoil due to their inherent elastic fibres. This decreases thoracic cavity volume
increasing intrapleural pressure. The lungs can compress (during forced expiration) and their volume
decreases. The pressure in the alveoli is now greater than atmospheric pressure and air moves out of
the lungs down its pressure gradient.

Question 27

What can the malfunction of the pleural membrane cause

Answer 27

The malfunction of the pleural membrane can cause certain diseased states particularly when gases
begin to enter the pleural cavity.

Question 28

In a healthy lung what is the pressure of the in intrapleural membrane

Answer 28

In a healthy lung, the pressure in the intrapleural membrane is
slightly negative relative to the lung. This is the force that pulls the lungs towards the chest wall.

Question 29

What happens when the pleural membranes are ruptured

Answer 29

If

either of the pleural membranes are ruptured, this negative pressure is lost.

Question 30

What can an injury to the chest cause

Answer 30

An external injury to
chest for example can cause a gap for air to pass between the interpleural space and the outside that
results in a balancing in pressures. This is due to air travelling down its pressure gradient that
increases the volume of the interpleural membrane. There is also no longer any pressure pulling the
lungs towards the chest wall and the lung just recoils and collapses at a low volume.

Question 31

What causes an open pneumothorax

Answer 31

There are in fact
various injuries that can cause this to occur. An open pneumothorax is caused by injury to one of the
pleural membranes of the lungs.

Question 32

What causes parietal pleura injury and visceral pleura

Answer 32

Injury to the parietal pleura can be caused externally whilst internal
rupturing of the visceral pleura can be caused by lung cancer.

Question 33

What causes closed pneumothorax

Answer 33

A closed pneumothorax is caused by air
entering the interpleural space without there being any external wound to either pleurae. This can
be caused by diseases like cancer and cystic fibrosis.

Question 34

What is the most common type of closed pneumothorax

Answer 34

The most common type of closed pneumothorax
is spontaneous pneumothorax that has an unknown cause. There are however different lobes of the
lung that can be independently affected by a pneumothorax as the lobes divide the lung up. This
means in lesser injuries, pneumothorax only causes parts of the lung to collapse. In more serious
injuries however, the whole lung does collapse. The partial lung collapse can temporarily prevent
under oxygenation of the blood (hypoxia) however this is not permanent.