Yan S D, Qiu Z M, Zhou N S
Department of Anatomy, Fujian Medical College, China.
Acta Anat (Basel). 1988;131(4):332-7.
The normal secondary tympanic membrane in human fetuses was examined by transmission electron microscopy. The membranes in 5- to 9-month-old fetuses consist of the following three layers: (1) an outer squamous epithelial layer facing the middle ear, which is not formed until 4 months old; (2) a middle fibrous layer containing collagen, elastin, fibroblasts and fibrocytes, and (3) an inner layer of flat cells facing the scala tympani. Following the maturation of the fetus the epithelium is getting thinner and fibroblasts are reduced in number, but fibrocytes are increased and collagen and elastin grow gradually in density. The ultrastructure of the secondary tympanic membrane at 8 month is mature in type and shows the same characteristics as in the adult. This membrane has an important and complicated physiological function. The epithelium of the outer layer, with tight junctions and multiple desmosomes, provides a barrier to keep harmful substances out. The stability of the membrane provides protection against rupture, while the elasticity plays a role in the physiology of hearing as well.
利用透射电子显微镜对人类胎儿正常的第二鼓膜进行了检查。5至9个月大胎儿的鼓膜由以下三层组成：（1）面向中耳的外层鳞状上皮层，直到4个月大时才形成；（2）中间的纤维层，含有胶原蛋白、弹性蛋白、成纤维细胞和纤维细胞；（3）面向鼓阶的扁平细胞内层。随着胎儿的成熟，上皮层变薄，成纤维细胞数量减少，但纤维细胞数量增加，胶原蛋白和弹性蛋白的密度逐渐增大。8个月时第二鼓膜的超微结构在类型上成熟，显示出与成人相同的特征。该膜具有重要而复杂的生理功能。外层上皮具有紧密连接和多个桥粒，形成一道屏障以阻挡有害物质。膜的稳定性可防止破裂，而弹性在听力生理中也发挥作用。
