Flashcards in 2.Anatomy of chest wall and mechanics of breathing Deck (75):
what are the 4 main gas laws?
- Boyle's Law
- Charles law
what is Boyle's law?
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)
what is Dalton's law?
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)
what is Charles' law?
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)
what is Henry's law?
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)
what structures are in the upper respiratory tract? (4)
what structure are in the lower respiratory tract? (3)
what structure encloses the lower respiratory tract?
the thorax, bounded by the ribs, spine and the diaphragm
do gases move across concentration gradient?
Yes; from areas of high pressure to areas of low pressure
what is each lung enclosed in?
what are the two pleural membranes?
parietal pleura and visceral pleura (membranes)
what type of muscle is the diaphragm?
what is found between the parietal and visceral pleuras?
where does the parietal pleura sit?
-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)
where does the visceral pleura sit?
coats the surface of lungs and is in direct contact with the lungs.
what is found in the pleural cavity?
parietal fluid (serous fluid)
how much of the pleural fluid (serous fluid) is found in the pleural cavity?
what is the function of pleural fluid (serous fluid)? (2)
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)
what is pleurisy?
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
what is the order of pleurae and pleural spaces from outer surface of lungs onwards? (5)
1. outer surface of lungs
2. visceral pleural membrane
3. pleural fluid
4. parietal pleural membrane
5. inner surface of the rib cage
what does visceral pleura coat?
outer surface of lungs
what does the parietal pleura coat?
inner surface of the ribs
what effectively sticks the lungs to the ribcage?
relationship of the pleural membranes
what causes the lungs to expand and pull the chest inward and outward?
elastic recoil of the lung which are stretched
why is this relationship between pleural membranes so important
-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
what keep the chest wall expansion and lung recoil in equilibrium?
the pleural fluid
why can't the chest expand too much (increase,outwards) and the lungs cannot recoil too much (decrease, inwards)?
because of the pleurae being stuck together and acting in unison
what can happen if some air gets into the pleural space and results in the loss of this sticking relationship?
pneumothroax (lung collapses)
because of which law can mechanics of breathing occur? and why?
Boyle's law; it occurs because the thoracic cavity changes volume
what effect does increased volume have on pressure?
what effect does decreased volume have on pressure?
in what direction do gases always travel in?
from area of high pressure to low pressure
what muscles does inspiration mainly use? (4)
-external intercostal muscles
- the diaphragm
what muscles does expiration mainly use during severe respiratory load? (3)
- internal intercostal muscles
why are muscles used during expiration only during severe respiratory load? (e.g. during sighing)
because expiration is passive at rest (muscles are relaxed and air is automatically released) whereas inspiration requires input of energy
what is the general relationship between pleural pressure and atmospheric pressure?
pleural pressure is always LESS than atmospheric pressure
what happens during inspiration in terms of pressures?
-pressure decreases inside lungs whereas atmospheric pressure is higher.
-air moves INTO the lungs across conc. gradient
- air is breathed in
what happens during expiration in terms of pressures?
- pressure increases inside lungs whereas atmospheric pressure is lower
-air moves OUT of the lungs across the conc. gradient
- air is breathed out
how do internal intercostal muscles run in the ribcage?
from upper border of one rib to upper border of another rib
what action do internal intercostal muscles mainly do?
move ribcage inwards and outwards allowing thoracic cavity to expand
what happens to most internal intercostal muscles during expiration?
which thoracic dimensions does inspiration increases? (3)
- anterior-posterior dimension
why does the diaphragm contract?
to increase thoracic volume (for max. air intake)
what causes asthma?
-over-reactive constriction of bronchial smooth muscle
-increases resistance which makes expiration difficult
what happens to airways during inspiration?
airways are pulled open by physical forces of inspiration
what happens to airways during expiration?
airways are compressed by physical forces of expiration
when is bronchial smooth muscle mainly activated in non-asthmatics?
if noxious/harmful particles are breathed in such as smoke
what happens to the bronchial smooth muscle in asthmatics?
- 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
what common clinical feature often helps clinicians diagnose asthma?
wheezing during expiration (because of exaggerated constriction)
what is intra-pleural pressure described as if it's less than atmospheric pressure?
subatmospheric pressure (e.g. -3mm Hg)
Describe what happens during a pneumothorax
-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
what is intra-thoracic pressure (alveolar pressure)?- Pa
pressure inside the thoracic cavity (essentially inside the lungs)
what is the intra-thoracic pressure (alveolar pressure) in terms of positivity/negativity?
may be positive OR negative compared to atmospheric pressure (decreased causes inhalation, increased causes expiration)
what is intra-pleural pressure?- Pip
pressure inside the pleural cavity
what is intra-pleural pressure in terms of positivity/ negativity
ALWAYS negative (at least in healthy humans)
what is transpulmonary pressure? -Pt
difference between alveolar pressure and intra-pleural pressure
what is transpulmonary pressure in terms of positivity/ negativity?
ALWAYS positive (at least in healthy humans); because Pip is always negative
Pt= Pa - (-Pip)
what are all pressures always compared to?
atmospheric pressure (0)
what is alveolar pressure like during inspiration?
less than atmospheric pressure (-ve)
what changes the intra-pleural pressure with each breath?
the ribcage constantly pulling away from the lungs
what is inspiration in terms of alveolar and intrapleural pressures?
when alveolar and intrapleural pressure is less than atmospheric
what is expiration in terms of alveolar and intrapleural pressure?
when alveolar and intrapleural pressure is more than atmospheric
during inspiration, is there a bigger drop in pressure in alveolar or intrapleural pressures?
in intrapleural (steeper curve); also steeper curve moving upwards during expiration during pressure increase
what is the bulk flow of air between the atmosphere and alveoli proportional to?
the difference between the atmospheric and alveolar pressures and inversely proportional to the airway resistance
the dimensions of the lungs and thoracic cage are stable as a result of opposing elastic forces during which stage of breathing?
between breaths at the end of unforced expiration (when no air is flowing in)
What creates a subatmospheric intrapleural pressure and hence the transpulmonary pressure that opposes the forces of elastic recoil?
The lungs are stretched and are attempting to recoil whereas the chest wall is compressed and attempting to move outward
what does airway resistance determine?
how much air flows into the lungs at any given pressure difference between atmosphere and alveoli
what is used as the major determinant of airway resistance?
radii of airways
what does lung volume depend upon? (2)
- the difference across the lungs (transpulmonary pressure)
- how stretchable the lungs are
what 2 muscles mainly increase the volume of the thoracic cage?
2. inspiratory (external) intercostal muscles
what effect does inspiration have on intrapleural pressure?
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
what happens to the chest wall during expiration?
-inspiratory muscles cease contracting allowing the elastic recoil of the chest wall and lungs to return them to their original between-breath size
what happens to alveoli during expiration?
-alveolar air is compressed
-alveolar pressure is above atmospheric pressure and drives air OUT of lungs
what muscles are used during FORCED expirations?
1. internal intercostal muscles
2. abdominal muscles