Law of Laplace and surface tension PPT Flashcards
josh's study session
Tension defined
the internal force generated by a structure
Law of laPlace states that for cylindrically shaped structures the formula is what?
T=Pr
T=wall tension
P= pressure of liquid in cylinder
r= radius
what does the law of LaPlace show or mean ( a lose definition)
as a structure expands its radius, wall tension increases
How is this law applied to real life?
Aortic aneurysms is more likely to rupture than a normal segment of the aorta b/c the radius is greater = increased wall tension
also capillary will withstand a pressure of 100mmHg better than a vein b/c capillary has a tiny radius compared to a vein
How does the law of LaPlace work with Spheres?
The ratio is doubled
2T=Pr
or (T= Pr/2)
how is LaPlaces law applied to real life in spheres
the LV, the greater the filling pressure, the greater the tension in the ventricular wall.
LaPlaces law in the alveoli
2T=Pr
or
P=2T/r
Laplaces law in the alveoli states that pressure needed to expand an alveolus is diresctly proprtional to__1__ and inversly proportional to __2__
1) surface tension
2) radius
P=2T/r
Alveoli are unique spheres b/c why?
they have H20 covered membrane
and water has surface tension
Alveoli act like bubbles and bubbles tend to pull toward what? and do what?
pull toward a smaller radius and collapse
the collapse of the alveoli is driven by what?
surface tension of H2O
van der Wall’s forces
what is the cumulative effects of cohesive intermolecular forces on the surface of a fluid at a liquid/gas or liquid/liquid interface
Surface tension
In the alveoli surface tension is _____ ____
wall tension
Law of Laplace explains what in the Alveoli
what would happen in the alveoli if not for surfactant
- smaller alveoli would empty into larger alveoli
- smaller alveolar spheres would be more difficult to expand than large alveoli
surfactant is composed of what?
dipalmityl phosphatidylcholine and Phospholipids (lecithin and spingomyelin) secreted by the alveolar (type II) cells
We all know that small alveoli are not harder to inflate compared to large alveoli. If this was true we wouldn’t have such well matched ventilation and perfusion ratios. thus we know that sufactant lowers __1__. and that small alveoli have more concentrated __2__ vs expanded (larger) alveoli and thus are easier to expand. so __3___ radius ___4___ surface tension by ___5___ surfactant concentrations
1) surface tension
2) surfactant
3) decreaseing
4) decreases
5) increasing
T=Pr example in Normal Alveoli
if r decreases, T decreases with P constant
- pressure in alveoli doesn’t change
- surfactant is the great equalizer
- explainds why small alveoli don’t empty into large alveoli in normal lungs
what cause the alveoli to collapse?
the water
without it they would stay open like a shopping bag
With adequate alveolar gas flow normal ventilatory to perfusion ration of _____ should be maintained
0.8
V/Q mismatch occurs with what?
inadequate flows
Alveolar Gas equation relates what to what?
PAO2 to FiO2
Formula for Aveolar Gas Equation
PAO2 = Fio2 x (Patm - PH2O) - PaCO2 / RQ PAO2= alveolar oxygen tension FiO2= inspired O2 concentration Patm= 760 mmHg PH20= 47 mmHg @ body temp PCO2= 25-45 mmHg RQ= respiratory quotient (normal 0.8)
What is the shorcut for estimating PaO2 from FiO2
FiO2 < 50% multiply FiO2 by 5
FiO2 > 50% multiply FiO2 by 6
the product is calculated PaO2
ex 0.21 x 5 = 105
