Surfactant

Question 1

Laplace’s law

Answer 1

• states that the distending pressure (the pressure required to keep a sphere distended) is directly proportional to the surface tension (T) and inversely proportional to the radius (r).

P = 2T/r

• Assuming a constant surface tension, a sphere with a smaller radius will have a higher distending pressure than a larger sphere.
• When the above clamp is opened, air will flow down its pressure gradient (i.e., from the smaller sphere to the larger one)
• the smaller sphere will completely collapse while the larger sphere increases in size.
• Surfactant counteracts this effect by decreasing the surface tension as a sphere decreases in size
• As the inside area of the sphere decreases, the surfactant becomes more concentrated and thus is able to decrease surface tension to a greater extent.
• as a sphere grows larger, the surfactant molecules become more spread out and do not reduce the surface tension as much.
• surfactant reduces the variation in distending pressure amongst spheres of varying sizes, preventing the collapse of smaller spheres and the unchecked expansion of larger ones.
• surfactant helps to prevent smaller alveoli from collapsing during expiration, and assists in regulating alveolar expansion during inspiration to ensure that all alveoli expand at similar rates.
• Pulmonary surfactant is a physiologic substance made by type II alveolar epithelial cells in the lung
• mostly comprised of dipalmitoylphosphatidylcholine (DPPC), other lipids, and surfactant proteins.