Laplace's law

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T=\frac{PR}{2}

(For spheres at a steady-state where T=Tension, P=Pressure, R=Radius)

Demonstration

As a consequence of this, if two identical sorts of balloon are joined together with a tap, and one is more inflated than the other, on opening the tap, the little balloon will blow up the big one.

Pathological consequences

In emphysema, as alveoli increase in size, the tension increases causing further destruction. Similarly, in ventricular failure, as the size of the ventricle increases, the wall tension increases, increasing the work the heart has to do to contract.

It is also important in the biophysics of abdominal aortic aneurysms and in very distended bowel (e.g. bowel afffected by volvulus). In these situations, the greater the distension, the greater the tension in the respective walls and the greater the chance of rupture.

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