Bland R D
Department of Pediatrics, University of Utah School of Medicine, Salt Lake City 84132.
Am J Physiol. 1990 Aug;259(2 Pt 1):L30-7. doi: 10.1152/ajplung.1990.259.2.L30.
During fetal life, the mammalian lung is a secretory organ that serves no respiratory function. Its potential airspaces are filled with liquid that flows from the pulmonary circulation across the epithelium in response to the osmotic force generated by Cl- secretion of airway and distal lung epithelial cells. As birth approaches, net Cl- secretion across the respiratory tract epithelium decreases, and this is associated with a reduction in the flow of liquid into the lung lumen. The cause for this change is unknown, but several recent studies indicate that it may be related to alterations in the hormonal milieu to which the lung epithelium is exposed late in gestation. The switch from placental to pulmonary gas exchange at birth requires rapid removal of liquid from the lung lumen. During labor and the immediate postnatal period, the pulmonary epithelium changes from a predominantly Cl- secreting membrane to a predominantly Na(+)-absorbing membrane, with resultant reversal of the direction of flow of lung liquid. There is considerable evidence that this change reflects an active metabolic process involving increased Na(+)-K(+)-ATPase activity in lung epithelial cells, which drives liquid from the lung lumen into the interstitium, with subsequent absorption into the pulmonary circulation.
在胎儿期，哺乳动物的肺是一个分泌器官，不具备呼吸功能。其潜在的气腔充满液体，这些液体从肺循环流经上皮细胞，这是对气道和肺远端上皮细胞分泌氯离子所产生的渗透力的响应。随着出生临近，呼吸道上皮细胞的净氯离子分泌减少，这与进入肺腔的液体流量减少有关。这种变化的原因尚不清楚，但最近的几项研究表明，这可能与妊娠后期肺上皮细胞所接触的激素环境的改变有关。出生时从胎盘气体交换转变为肺气体交换需要迅速清除肺腔内的液体。在分娩期间及产后即刻，肺上皮细胞从主要分泌氯离子的膜转变为主要吸收钠离子的膜，从而导致肺液流动方向逆转。有大量证据表明，这种变化反映了一个活跃的代谢过程，涉及肺上皮细胞中钠钾ATP酶活性增加，该酶将液体从肺腔驱入间质，随后被吸收进入肺循环。
