L19-Elastic properties Flashcards
(22 cards)
Define Elasticity
-Resistance of an object to deformation by external force (or stiffness, resistant to stretch.
‘Desire to go back to the original shape’-DONT WRITE THIS
Define Compliance
the ability to stretch
Relationship between compliance and elasticity
MORE ELASTIC something is the LESS COMPLIANT it is.
Elasticity refers to how much something resists being stretched and how quickly it returns to its original shape.
Compliance refers to how easily something stretches in response to an applied force.
Ie:
-A tight rubber band has high elasticity (it snaps back quickly after being stretched) but low compliance (it takes a lot of force to stretch it).
-A balloon has low elasticity (it doesn’t snap back as forcefully) but high compliance (it expands easily when air is added).
-A highly elastic lung resists stretching and has low compliance (harder to expand).
A low elastic lung stretches easily and has high compliance (expands readily).
This is why diseases like pulmonary fibrosis (where the lung tissue becomes stiffer and more elastic) cause reduced lung compliance, making breathing more difficult.
what happens to the lung distending pressure during inspiration
lung distending pressure is more +ve > lung more distended.
What does the degree of lung expansion or the change in the lung volume depends on what ?
it is proportional to the distending pressure.
Generating a greater outward, distending pressure leads to a greater change in lung volume.
draw a pressure -volume curve for the lung
‘lung compliance curve’
Define interstitial fibrosis in terms of volume and pressure graph.
decreased compliance (more elastic- higher resistance) so the patient have to work harder.
- a larger than normal change in pressure needed to inflate lung ( more work ).
Define Emphysema
increased compliance (less elastic) so the lung wall and millions of tiny villi collapsed.
-a smaller change in distending pressure leads to large change in volume(less work)
What determines the compliance of the lung?
-the elastic properties of tissue. (elastic connective tissue forces) > thickening lung tissue 👇ses compliance.
-surface tension - air-water interfaces within alveoli (accounts for > half lung elastic recoil)
what is surface tension, example? and how is it made?
-collapsing force. alveolar lining fluid generates significant surface tension.
- surface tension in alveoli 10% of theoretical value
- due to release of SURFACTANT from type 2 cells
What would high surface tension cause ?
normally collapse alveoli.
How does the surfactant molecules interact with water molecules?
Surfactant molecules have
strong attraction for each other
but low attraction for other
molecules – accumulate at
surface and reduce surface
tension.
What if there is no surfactant ?
compliance would 👇se
Effects of surface tension and the law?
-bubble forms a sphere as small as possible.
-surface tension tends to shrink the bubble.
-P = 2T / r
T=surface tension force
r=radius
Laplace’s Law
Why don’t smaller alveoli collapse into larger alveoli?
P = 2T / r
If r1< r2, then P1>P2
-surfactant reduces T so P is same in alveoli with different r.
-now P1(bigger alveoli) = P2(smaller alveoli)
How does the surfactant work in a small area of alveoli?
- smaller radius alveoli (lower surface area) so the surfactants are more closer.
- > density of surfactant
- more effective at reducing surface tension
in smaller alveoli and during deflation of
the lung (expiration)
What about the distending pressure of chest wall?
Chest distending pressure
is always negative (tries to
push chest in).
How compliant is the chest wall ?
The chest wall has moderate compliance, meaning it expands and recoils relatively easily but still resists extreme deformation.
what’s the pressure in all of the alveoli?
same and stable otherwise they would all collapse.
Conditions that change the compliance of the chest wall
-scoliosis
-kyphosis
-curvature spine
-pectus excavatum
-obesity
Explain the graph with both lung compliance and chest wall added together ?
LOOK AT SAMSUNG NOTEs
