anatomy of chest wall and breathing mechanics Flashcards
Describe how the muscles of respiration act to inc and dec thoracic volume:
muscles of inspiration – the diaphragm, external intercostals, sternocleidomastoid and scalenes.
muscles of expiration – the internal intercostals and abdominals
Expiration is passive at rest, their muscles are utilised in severe respiratory load.
As the diaphragm contracts it moves down which increases the thoracic volume which leads to a drop in pressure which pulls air into the lungs
describe what the parietal and visceral pleura does:
Visceral pleural membrane – coats the outer surface of the lungs
Parietal pleural membrane – coats the inner surface of ribs
Relate Boyle’s law to the mechanics of breathing:
Boyle’s law states in a closed space, the pressure exerted by a gas is inversely proportional to its volume
Therefore an increase in volume leads to a decrease in pressure and a decrease in volume leads to an increase in pressure
Explain why intrapleural pressure is always less than alveolar pressure:
The pleural cavity is always lined by a thin layer of fluid that’s secreted by the visceral layer of the pleura.
This fluid is constantly pumped from the pleural cavity into lymphatic vessels.
The pumping of fluid creates the negative pressure in the pleural cavity.
This keeps the lungs always inflated.
atmospheric due to recoil mechanism of chest wall (outward) and lungs (inwards)
what is anatomical dead space?
vol of gas occupied by conducting airways that is NOT available for gas exchange (150mL)
what is tidal volume (TV)?
Vol breathed in or out at each breath (500mL)
what is expiratory reserve volume (ERV)?
Max vol of air which can be forcefully expired from lungs at the end of a normal expiration (1100mL)
what is inspiratory reserve volume (IRV)?
Max vol of air which can be forcefullu inhaled into lungs at the end of normal inspiration (3000mL)
what is residual volume (RV)?
The vol of gas in lungs at the end of maximal expiration (1200mL)
what is vital capacity?
Tidal vol + IRV + ERV (4600mL)
what is total lung capacity?
Vital capacity + RV (5800mL)
what is inspiratory capacity?
TV + IRV (3500mL)
what is functional capacity?
ERV + RV (2300mL)
surfactant production
type 2 alveolar cell production starts at 25 weeks and is complete by 36 weeks.
what is surfactant stimulated by?
It is stimulated by thyroid hormones and cortisol
what is the role of surfactant?
decreases surface tension therefore lowering the risk of alveoli collapsing
it also decreases the lungs’ tendency to recoil and make breathing easier
when does surfactant tension occur?
where there is an air-water interface, and refers to the attraction between water molecules.
why is surfactant also effective in small alveoli?
as the surfactant molecules come closer together therefore increasing the concentration
explain what the law of Laplace is:
The law of LaPlace states that pressure is higher in smaller alveoli (P=2T/r)
Where T is surface tension, r is radius and P is pressure
what is compliance and how it’s affected?
the change in volume relative to the change in pressure.
It is affected by disease (emphysema etc.) and is also affected by age.
Compliance represents the stretchability of the lungs
High compliance = large increase in lung volume for a small decrease in IP pressure
Low compliance = small inc in lung volume for a large decrease in IP pressure
physiological dead space
total volume of the respiratory system where gas exchange does not occur effectively
anatomical + alveolar
alveolar dead space
ventilation > perfusion
alveoli that are ventilated but not perfused so can’t participate in gas exchange
