Fig. 4.

Transmission electron micrographs. a Transcapillary pillar formation indicates the occurrence of intussusceptive angiogenesis during compensatory lung growth which can be seen as protrusive interendothelial junctions. Pil denotes pillar, al alveolus, am alveolar membrane, ec endothelial cell; Bar = 10 μm b Semi-thin sections reveal the close spatial relationship between alveolar macrophages (black stars) and type II pneumocytes (red arrowheads), indicated in the subpleural region (P _L : pleura). Bar = 50 μm c, d Appearance of monocytes, alveolar macrophages, and type II pneumocytes indicates their proangiogenic relevance for alveolar morphogenesis. ATII, type II pneumocytes; mo monocyte; c capillary; MΦ; alveolar macrophage. c Bar = 15 μm; d Bar = 30 μm