2.Anatomy of chest wall and mechanics of breathing

Question 1

what are the 4 main gas laws?

Answer 1

• Boyle’s Law
• Dalton’s law
• Charles law
• Henry’s law

Question 2

what is Boyle’s law?

Answer 2

states that the pressure exerted by a gas is inversely proportional to its volume (e.g. as you increase container volume the pressure is contained in, the pressure will decrease)

Question 3

what is Dalton’s law?

Answer 3

states that the total pressure of a gas mixture is the sum of the pressures of the individual gases (combines the pressures of the mixture of gases in the air; oxygen, nitrogen, hydrogen and CO2)

Question 4

what is Charles’ law?

Answer 4

states that the volume occupied by a gas is directly related to the absolute temperature (temperature of the environment is related to volume of gas)

Question 5

what is Henry’s law?

Answer 5

states that the amount of gas dissolved in a liquid is determined by the pressure of the gas and its solubility in the liquid (e.g. oxygen is not soluble in water, yet plasma is 90% water- this is why haemoglobin is used for O2 transport)

Question 6

what structures are in the upper respiratory tract? (4)

Answer 6

1. mouth
2. nasal cavity
3. pharynx
4. larynx

Question 7

what structure are in the lower respiratory tract? (3)

Answer 7

1. trachea
2. bronchi
3. lungs

Question 8

what structure encloses the lower respiratory tract?

Answer 8

the thorax, bounded by the ribs, spine and the diaphragm

Question 9

do gases move across concentration gradient?

Answer 9

Yes; from areas of high pressure to areas of low pressure

Question 10

what is each lung enclosed in?

Answer 10

pleural membranes

Question 11

what are the two pleural membranes?

Answer 11

parietal pleura and visceral pleura (membranes)

Question 12

what type of muscle is the diaphragm?

Answer 12

skeletal muscle

Question 13

what is found between the parietal and visceral pleuras?

Answer 13

pleural cavity

Question 14

where does the parietal pleura sit?

Answer 14

• it’s a continuos membrane which encompasses the lungs

- sits on the inside of ribs on the surface of diaphragm below (in contact with both)

Question 15

where does the visceral pleura sit?

Answer 15

coats the surface of lungs and is in direct contact with the lungs.

Question 16

what is found in the pleural cavity?

Answer 16

parietal fluid (serous fluid)

Question 17

how much of the pleural fluid (serous fluid) is found in the pleural cavity?

Answer 17

around 3ml

Question 18

what is the function of pleural fluid (serous fluid)? (2)

Answer 18

1. acts as a lubricant allowing lungs to glide smoothly across the ribs
2. prevents lungs and ribs from separating from each other (like putting water on 2 glass slides, creating a sliding and sticking action)

Question 19

what is pleurisy?

Answer 19

pleural space/cavity can be invaded by air, fluid or particles which result in inflammation of the pleurae (lung membranes) and makes breathing more difficult

Question 20

what is the order of pleurae and pleural spaces from outer surface of lungs onwards? (5)

Answer 20

1. outer surface of lungs
2. visceral pleural membrane
3. pleural fluid
4. parietal pleural membrane
5. inner surface of the rib cage

Question 21

what does visceral pleura coat?

Answer 21

outer surface of lungs

Question 22

what does the parietal pleura coat?

Answer 22

inner surface of the ribs

Question 23

what effectively sticks the lungs to the ribcage?

Answer 23

relationship of the pleural membranes

Question 24

what causes the lungs to expand and pull the chest inward and outward?

Answer 24

elastic recoil of the lung which are stretched

Question 25

why is this relationship between pleural membranes so important

Answer 25

-During normal repsiration, the chest wall expands more than it wants to, whereas the lungs want to recoil. The two forces are held in equilibrium

Question 26

what keep the chest wall expansion and lung recoil in equilibrium?

Answer 26

the pleural fluid

Question 27

why can't the chest expand too much (increase,outwards) and the lungs cannot recoil too much (decrease, inwards)?

Answer 27

because of the pleurae being stuck together and acting in unison

Question 28

what can happen if some air gets into the pleural space and results in the loss of this sticking relationship?

Answer 28

pneumothroax (lung collapses)

Question 29

because of which law can mechanics of breathing occur? and why?

Answer 29

Boyle's law; it occurs because the thoracic cavity changes volume

Question 30

what effect does increased volume have on pressure?

Answer 30

decreases pressure

Question 31

what effect does decreased volume have on pressure?

Answer 31

increases pressure

Question 32

in what direction do gases always travel in?

Answer 32

from area of high pressure to low pressure

Question 33

what muscles does inspiration mainly use? (4)

Answer 33

- external intercostal muscles - the diaphragm - sternocleidomastoids - scalenes

Question 34

what muscles does expiration mainly use during severe respiratory load? (3)

Answer 34

- internal intercostal muscles - diaphragm - abdominal muscles

Question 35

why are muscles used during expiration only during severe respiratory load? (e.g. during sighing)

Answer 35

because expiration is passive at rest (muscles are relaxed and air is automatically released) whereas inspiration requires input of energy

Question 36

what is the general relationship between pleural pressure and atmospheric pressure?

Answer 36

pleural pressure is always LESS than atmospheric pressure

Question 37

what happens during inspiration in terms of pressures?

Answer 37

- pressure decreases inside lungs whereas atmospheric pressure is higher. - air moves INTO the lungs across conc. gradient - air is breathed in

Question 38

what happens during expiration in terms of pressures?

Answer 38

- pressure increases inside lungs whereas atmospheric pressure is lower - air moves OUT of the lungs across the conc. gradient - air is breathed out

Question 39

how do internal intercostal muscles run in the ribcage?

Answer 39

from upper border of one rib to upper border of another rib

Question 40

what action do internal intercostal muscles mainly do?

Answer 40

move ribcage inwards and outwards allowing thoracic cavity to expand

Question 41

what happens to most internal intercostal muscles during expiration?

Answer 41

they relax

Question 42

which thoracic dimensions does inspiration increases? (3)

Answer 42

- anterior-posterior dimension - medio-lateral dimension - superior-inferior dimensions

Question 43

why does the diaphragm contract?

Answer 43

to increase thoracic volume (for max. air intake)

Question 44

what causes asthma?

Answer 44

- over-reactive constriction of bronchial smooth muscle | - increases resistance which makes expiration difficult

Question 45

what happens to airways during inspiration?

Answer 45

airways are pulled open by physical forces of inspiration

Question 46

what happens to airways during expiration?

Answer 46

airways are compressed by physical forces of expiration

Question 47

when is bronchial smooth muscle mainly activated in non-asthmatics?

Answer 47

if noxious/harmful particles are breathed in such as smoke

Question 48

what happens to the bronchial smooth muscle in asthmatics?

Answer 48

- it's active during normal breathing - during expiration, the over-reactive constriction of bronchial smooth muscle is even more exaggerated which stimulates the compression of airways

Question 49

what common clinical feature often helps clinicians diagnose asthma?

Answer 49

wheezing during expiration (because of exaggerated constriction)

Question 50

what is intra-pleural pressure described as if it's less than atmospheric pressure?

Answer 50

subatmospheric pressure (e.g. -3mm Hg)

Question 51

Describe what happens during a pneumothorax

Answer 51

- Air is found in the pleural cavity which causes air buildup - as air continues to increase, this puts pressure against the lungs causing it to collapse and become non-functional

Question 52

what is intra-thoracic pressure (alveolar pressure)?- Pa

Answer 52

pressure inside the thoracic cavity (essentially inside the lungs)

Question 53

what is the intra-thoracic pressure (alveolar pressure) in terms of positivity/negativity?

Answer 53

may be positive OR negative compared to atmospheric pressure (decreased causes inhalation, increased causes expiration)

Question 54

what is intra-pleural pressure?- Pip

Answer 54

pressure inside the pleural cavity

Question 55

what is intra-pleural pressure in terms of positivity/ negativity

Answer 55

ALWAYS negative (at least in healthy humans)

Question 56

what is transpulmonary pressure? -Pt

Answer 56

difference between alveolar pressure and intra-pleural pressure

Question 57

what is transpulmonary pressure in terms of positivity/ negativity?

Answer 57

``` ALWAYS positive (at least in healthy humans); because Pip is always negative Pt= Pa - (-Pip) ```

Question 58

what are all pressures always compared to?

Answer 58

atmospheric pressure (0)

Question 59

what is alveolar pressure like during inspiration?

Answer 59

less than atmospheric pressure (-ve)

Question 60

what changes the intra-pleural pressure with each breath?

Answer 60

the ribcage constantly pulling away from the lungs

Question 61

what is inspiration in terms of alveolar and intrapleural pressures?

Answer 61

when alveolar and intrapleural pressure is less than atmospheric

Question 62

what is expiration in terms of alveolar and intrapleural pressure?

Answer 62

when alveolar and intrapleural pressure is more than atmospheric

Question 63

during inspiration, is there a bigger drop in pressure in alveolar or intrapleural pressures?

Answer 63

in intrapleural (steeper curve); also steeper curve moving upwards during expiration during pressure increase

Question 64

what is the bulk flow of air between the atmosphere and alveoli proportional to?

Answer 64

the difference between the atmospheric and alveolar pressures and inversely proportional to the airway resistance

Question 65

the dimensions of the lungs and thoracic cage are stable as a result of opposing elastic forces during which stage of breathing?

Answer 65

between breaths at the end of unforced expiration (when no air is flowing in)

Question 66

What creates a subatmospheric intrapleural pressure and hence the transpulmonary pressure that opposes the forces of elastic recoil?

Answer 66

The lungs are stretched and are attempting to recoil whereas the chest wall is compressed and attempting to move outward

Question 67

what does airway resistance determine?

Answer 67

how much air flows into the lungs at any given pressure difference between atmosphere and alveoli

Question 68

what is used as the major determinant of airway resistance?

Answer 68

radii of airways

Question 69

what does lung volume depend upon? (2)

Answer 69

- the difference across the lungs (transpulmonary pressure) | - how stretchable the lungs are

Question 70

what 2 muscles mainly increase the volume of the thoracic cage?

Answer 70

1. diaphragm | 2. inspiratory (external) intercostal muscles

Question 71

what effect does inspiration have on intrapleural pressure?

Answer 71

Makes it more negative (subatmospheric) and causes the lungs to expand and make the alveolar pressure subatmospheric which creates the pressure difference between atmosphere and alveoli to drive air flow INTO the lungs

Question 72

what happens to the chest wall during expiration?

Answer 72

-inspiratory muscles cease contracting allowing the elastic recoil of the chest wall and lungs to return them to their original between-breath size

Question 73

what happens to alveoli during expiration?

Answer 73

- alveolar air is compressed | - alveolar pressure is above atmospheric pressure and drives air OUT of lungs

Question 74

what muscles are used during FORCED expirations?

Answer 74

1. internal intercostal muscles | 2. abdominal muscles

Question 75

what effect does expiration have on the chest wall?

Answer 75

- decreases thoracic dimensions | - reduces breathing cycle and allowing more breaths/min