combined lung and chest-wall system is less than that of either structure alone (like a balloon in a balloon) [nb the combined compliance curve changes with diseases] Emphysema (increased lung compliance). Emphysema is associated with loss of elastic fibers in the lungs. Reduced collapsing at a given volume Thus, the combined lung and chest-wall system seeks a new higher FRC, where the two opposing forces can be balanced breathe at higher lung volumes (in recognition of the higher FRC) and will have a barrel-shaped chest. Fibrosis (decreased lung compliance) stiffening of lung tissues Increased collapsing force at a given volume Thus, the combined lung and system seeks a new lower FRC, where the two opposing forces can be balanced breathe at lung volumes Keeping the alveoli open during inspiration: the alveolar pressure is negative during this period so think they would want to collapse Alveoli can be considered as gas bubbles in a liquid so can use the Law of Laplace Law of Laplace states that P = 2T/R for such a bubble to be stable and to stop collapsing, P = pressure at which the bubble is stable (want it to be low), T=tension (ie low allows for lower pressure) and R=radius (ie high allows for lower pressure) Hence smaller alveoli require larger pressures to remain open and should be the first to collapse This problem is avoided by a higher surfactant concentration at smaller alveoli; the surfactant (produced by type II pneumocytes) lowers surface tension to allow alveoli stability at reduced pressures and by using higher surfactant concentrations at smaller alveoli further reductions in surface tension are offered to compensate for their greater propensity to collapse. For a given drop in pressure, as alveoli start to shrink (reducing R, radius) the tension (T, surface tension) falls faster, therefore will quickly reach a new set of R&T values that via the equation match the required P value which was previously too high. Surfactant info: Is dipalmatoylphosphatidyl choline mainly Has the lowest surface tension of any biological substance
combined lung and chest-wall system is less than that of either structure alone (like a balloon in a balloon) [nb the combined compliance curve changes with diseases] Emphysema (increased lung compliance). Emphysema is associated with loss of elastic fibers in the lungs. Reduced collapsing at a given volume Thus, the combined lung and chest-wall system seeks a new higher FRC, where the two opposing forces can be balanced breathe at higher lung volumes (in recognition of the higher FRC) and will have a barrel-shaped chest. Fibrosis (decreased lung compliance) stiffening of lung tissues Increased collapsing force at a given volume Thus, the combined lung and system seeks a new lower FRC, where the two opposing forces can be balanced breathe at lung volumes Keeping the alveoli open during inspiration: the alveolar pressure is negative during this period so think they would want to collapse Alveoli can be considered as gas bubbles in a liquid so can use the Law of Laplace Law of Laplace states that P = 2T/R for such a bubble to be stable and to stop collapsing, P = pressure at which the bubble is stable (want it to be low), T=tension (ie low allows for lower pressure) and R=radius (ie high allows for lower pressure) Hence smaller alveoli require larger pressures to remain open and should be the first to collapse This problem is avoided by a higher surfactant concentration at smaller alveoli; the surfactant (produced by type II pneumocytes) lowers surface tension to allow alveoli stability at reduced pressures and by using higher surfactant concentrations at smaller alveoli further reductions in surface tension are offered to compensate for their greater propensity to collapse. For a given drop in pressure, as alveoli start to shrink (reducing R, radius) the tension (T, surface tension) falls faster, therefore will quickly reach a new set of R&T values that via the equation match the required P value which was previously too high. Surfactant info: Is dipalmatoylphosphatidyl choline mainly Has the lowest surface tension of any biological substance
Respiratory-notes-BETA.docx