人胚胎九个月视网膜组织超微形态学观察

目的 观察人胚胎9个月时视网膜组织结构,探讨出生前期视网膜内神经元发育特征及意义.方法 取因外伤自愿终止妊娠的9个月人胚胎2例4个眼球.1例孕周为35周,1例为36周.胎龄根据孕妇的末次月经及测量胚胎坐高而确定.每只眼球于后极部定位取材视网膜组织片4个,常规电子显微镜标本处理程序后进行观察.扫描电子显微镜(SEM)和透射电子显微镜(TEM)共观察视网膜样本8个.结果 胚胎9个月时,外核层内含有5～6层感光细胞,外界膜外侧散在分布直径为2～3 μm的球形膜性结构.感光细胞内节段排列紧密,其间可见含粘连小带的外界膜,内含线粒体.其外侧可见纤毛.外节段较小,其内可见少量排列欠整的盘膜结构.感光细胞为多形核,常和(或)异染色质比例接近.感光细胞轴突分支少而细,与内核层细胞间联系较少,未见典型的"突触"结构.视网膜内核层含4～5层胞体.多种胞核常和(或)异染色质密度不均,部分为分叶核,核膜清晰.内网状层内各神经细胞分枝细小,神经突起间联系较少,少见典型的"突触"结构.视网膜神经节细胞(RGC)数量较少,胞膜完整,胞浆内可见大的细胞核和粗面内质网,核膜为连续的双层膜性结构,核内以常染色质为主.视网膜内界膜为双层膜性结构,其内侧可见排列整齐的神经纤维层,表面分布直径2～3μm的微孔,其间散在4～5 μm的较大孔隙.结论胚胎9个月时,人视网膜组织各层结构已经形成.但部分细胞结构和细胞联系尚未成熟,提示此期人视网膜发育仍处于发育重塑的重要时期.

Observation on retinal ultrastructures of the human fetus at the gestational age of 9 months

Objective To observe the retinal ultrastructure of the human fetal at the age of 9 months, and to investigate the clinical significance of the observation on retinal neuron development during the prenatal period. Methods Four human fetal eyes of 2 fetus at the gestational age of 9 months, including 1 at 35 and the other at 36 weeks, were obtained after termination of pregnancy due to trauma. The gestational ages of the fetus were estimated according to both last menstrual period (LMP) of the pregnant women and the weight/crown-heel length of fetus at the delivery. From each eyeball, 4 pieces of retina at the posterior pole were obtained and observed after specimens handling according to the procedure of routine electron microscopy. Eight pieces of retina which were randomly selected from total of 16 pieces of retina in each group were processed and observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Permissions from pregnant women and family members were guaranteed. Results At the gestational age of 9 months, the outer nuclear layer of fetal retina contained 5 to 6 layers of photoreceptor cells (PRC), and spherical-like membrane structures were found outside of the outer limiting membrane (OLM). Among many tight-aligned inner segments of PRCs there was zonula adherens of OLM, mitochondrias at inner side of OLM, and cilium at outer side of OLM. Outer segment of PRCs were short and contained a few irregularly arranged disc membrane. Some PRC had a multi-shaped nucleus in which equal amount of euehromatin and heteroehromatin. There were only few and thin axon branches from photoreceptor cells, and very few axons contacted with inner nuclear layer (INL) and no typical synapse was found. The INL contained 4 to 5 layers of cell bodies, in which many cellular nuclear had uneven density of euchromatin and heterochromatin; some were lobulated nucleus with clear karyotheca. In inner plexiform layer (IPL), the nerve cells had small branches, and only little connection among the synapses and few synapse structures were found. Although not many retinal ganglion cells (RGC) existed, RGC had both intact cell membrane and some rough endoplasmic reticulum (RER). The karyotheca of RGC had double-layers structures, and the nucleus was mainly consisted of euchromatin. Internal limiting membrane (ILM) had double-layer membrane structures, and the well-arranged nerve fiber layer was located at the outer side of ILM, with some micropores on the surface. Conclusions At the gestational age of 9 months, all layers of the human retinal has been formed, but some cell structure and cell connections are not yet mature, suggesting that at this time of period, human retina is still at an important stage of developing and remodeling.