Mechanics of breathing 2 Flashcards
what is responsible for the elastic recoil of lungs and where is it found?
The alveoli themselves don’t contain muscle fibres as this would block rapid gas exchange. therefore cannot contract.
therefore the connective tissue between the alveolar epithelial cells contain many elastin and collagen fibres which create elastic recoil when the lung tissue is stretched.
pulmonary circulation is ….. pressure, ……. flow system
low pressure
high flow
what is the pulmonary arterial pressure?
25/8mmHg
why odes the right ventricle not have to pump as forcefully to create blood flow through the lungs?
The pulmonary circulation has low resistance due to;
- shorter length of pulmonary vessels
- dispensable and large total cross-sectional area of pulmonary arterioles.
what is the pressure of the intrapleural cavity?
-3mmHg (sub atmospheric)
during normal inspiration, what happens to the intrapleural pressure?
it decreases further to -6mmHg
during exercise, what happens to the intrapleural pressure during maximal inspiration?
it decreases further to -8mmHg
what happens to the rib cage in a pneumothorax?
the rib cage expands slightly due to the increase in air in the intra pleural cavity
what are the 2 factors which have the greatest influence on the amount of work needed for breathing?
the stretchability of the lungs
resistance of the airways to air flow
the ability of the lung to stretch is termed?
compliance
do lungs which have a high compliance normally have a high or low elasticity?
low elasticity
A lung which stretches easily has probably los its elastic tissue and will not return to its resting volume when the stretching force is released.
what happens to the elastin fibres in emphysema?
in emphysema the elastin fibres found in the lung tissue are destroyed.
describe the pathophysiology of emphysema.
In emphysema the elastin fibres are destroyed so there is a loss of elasticity.
The lungs have high compliance so are easily inflated (inspiration isn’t a problem) however during expiration there is no elastic recoil so air doesn’t leave the lungs.
Therefore use of accessory muscles are required to force air out.
what are the 2 common causes of decreased lung compliance causing restrictive lung diseases?
inelastic scar tissue formed in fibrotic lung diseases i.e. UIP
Inadequate alveolar production of surfactant
how does inhalation of fine particles such as asbestos cause pulmonary fibrosis?
Inhaled particles are ingested by alveolar macrophages.
If they are organic then they may be digested with lysosomal enzymes.
If the particles cannot be digested by the macrophages then an inflammatory process occurs.
The macrophage then secrete growth factors which stimulate fibroblasts in the lungs connective tissue to produce inelastic collagen.
what law describes the inward pressure created by surface tension in the alveoli?
law of La Place
what is the law of La Place equation?
P=2T/r
2x tension / radius
where is surfactant more concentrated and why?
The inward pressure in the small alveoli is greater therefore more surfactant is concentrated in smaller alveoli.
This is to reduce the surface tension in the small alveoli so it is less than that of large alveoli so the net inward pressure is equal.
what is the pressure of the atmosphere? and how much of this we breathe is oxygen?
760mmHg
21% is 02
what is the pressure of oxygen when it reaches our blood? and why?
100mmHg
it decreases from 160-100mmHg as it has been diluted, moistened and saturated by water vapour
when is surfactant produced in utero?
25 weeks
what stimulates the production of surfactant?
cortisol and thyroid hormones
what is compliance defined as?
change in volume relative to a change in pressure
(how much does the volume change for any given change in pressure)
e.g. high compliance is when just a small increase in pressure causes a large increase in volume
where in the lungs is compliance greatest?
the base
