Mechanisms for the generation of gas-exchange surface area in rat lung

development, rat lung seems to make use of the mechanisms of 1) expansion, 2) replication, and 3) subdivision to increase its gas-exchange surface area. To quantitate the contribution of each one of these mechanisms from birth to adulthood, four models of lung development have been mathematically evalu-ated: 1) existing saccules at birth septate (subdivide) during the first 2 postnatal weeks, creating smaller alveoli that undergo a continuous expansion up to adulthood; 2) same as the previous model except that new alveoli are also formed by means other than septation after the second postnatal week; 3) same as the previous model except that the alveoli formed by means other than septation start forming immediately after birth; and 4) saccules continue to be formed up to adulthood and subsequently septate, forming alveoli. In an evaluation of these models mathematically, it was found that expansio