Alveolar sacs consists of spaces surrounded by alveoli which appear as small compartments opening into the alveolar sac
肺泡：进行气体交换的部位，为多面形囊泡，开口于肺呼吸部各管道，其壁很薄，表面覆以单层上皮，称肺泡上皮。
However, the NOS activities in epithelial cells of bronchi, alveolar duct and sac, in hypoxic rats were not affected.
缺氧对支气管、肺泡管和肺泡囊上皮细胞NOS的活性无明显影响。
BMP may also be found in human tooth germs, predentin, the cells of outer and inner enamel epithelium, and the cells of dental sac generating alveolar bone.
在人的牙胚中，BMP主要分布在前期牙木质、外釉细胞和造釉细胞以及形成牙槽骨的牙囊细胞中，表明骨的生长和形成以及牙齿的发育都与BMR密切相关。
RESULTS: During tooth root patterning, expression of MSX1 was found not only in dental papilla of the apical area, dental sac and odontoblasts, but also in dental attachment apparatus such as cementoblast, periodontal supporting tissues and alveolar bone.
结果：在牙根发育不同时期内，MSX1mRNA不仅在牙乳头、牙囊组织及成牙本质细胞中有阳性表达，而且在牙附着组织，如成牙骨质细胞、上皮根鞘、牙周组织及根周牙槽骨组织中也有表达。