the law of laas named in honor of French scholar Pierre Simo laas is a law in physics that states that the tension in the walls of a hollow sphere or cylinder is dependent on the pressure of its contents and its radius the concept was then later applied to medicine since there are many Hollow spherical and cylindrical shaped organs in our bodies that deal with pressures important examples include the blood vessels and the chambers of the heart okay so according to the law of laas wall tension is proportional to pressure p * radius R now let's break it down the wall tension is the force in the container's walls that resists the force trying to expand it so if we're blowing up a balloon we can think of the wall tension as the force created by the elastic rubber wall that resists the outward Force applied by the pressure inside the balloon now if we break the wall tension into components we have a vertical Vector of four Force that's counteracting the expansion of the balloon and a horizontal Vector of force that's stretching and tearing the balloon's wall so for pressure if we were to blow more air into a balloon we would expect the pressure inside to build up and the wall tension of the balloon would increase as the walls push back against the expansion if the pressure trying to expand the balloon is greater than the wall tension the balloon will expand or pop now another factor is the radius a smaller radius means more pressure is needed to overcome the wall tension in order for the container to expand this is why it's harder to blow up a small deflated balloon than it is to blow up a half inflated balloon an example of this can be seen in the alvioli in the lungs of a newborn let's plug in some easy imaginary numbers and forgo units to make this concept easier to understand normally an unused Alvis in a newborn is collapsed so let's say it has a radius of two and the wall tension is eight the baby starts crying and inhales the pressure of the inhaled air in the Alvis is four so our equation is 4 * 2 which gives us 8 and since this is the same as the wall pressure the Alvis doesn't expand in other words the baby will need to breathe in enough air to generate greater than four units of pressure to inflate it now let's say that the Alvis has expanded after the baby took a few breaths and the radius is now four and the wall tension Remains the Same so this time the baby only needs to breathe in enough air to generate greater than two units of pressure to expand the Alvis so it takes a lot less work now a concept related to wall tension is wall stress which uses a modified version of lass's law that factors in the thickness of the wall the equation for wall stress is pressure time radius over 2 * the wall thickness based on this equation wall stress is wall tension divided by 2 * the wall thickness so the thicker the wall the less wall stress to see a real life example let's look at the heart more specifically the Chamber of the left ventricle which resembles a sturdy round cup let's say we have a person with aortic stenosis which means the aortic valve is narrowed and it makes it harder for blood to flow through in order to overcome this the heart will pump harder causing an increase in the pressure inside the heart and as a result we increase the wall tension now in order to push more blood out the left ventricle hypertrophies meaning the cardiac cells grow thicker by adding more sarir the contractile units of cardiac cells as a result there's an increase in the wall thickness and a decrease in the radius of the chamber and according to our equation both will reduce wall stress thanks to this the heart is less likely to tear open when under pressure all right as a quick recap the law of laass is a law in physics that states that the wall tension of a hollow sphere or cylinder is proportional to both the pressure of its contents and its radius wall stress is the wall tension divided by 2 times the wall thickness now when applied to hollow spherical objects like the left ventricle of the heart the following formula is used wall stress equals P * R / 2 W where p is pressure R is total radius and W is wall thickness in short the law of La plast states that wall tension is directly proportional to pressure and radius and while stress is proportional to the wall tension but inversely proportional to two times the wall thickness helping current and future clinicians Focus learn retain and Thrive learn more