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1 脐带的形成在胚胎早期从胚板的外胚层分化出中胚层组织,其背侧发育速度较腹侧快,使羊膜腔顶部与滋养层分离,随着神经管的延长,胚胎突出于羊膜腔中,而胚板尾部的中胚层细胞与滋养层相连向腹面包裹,将尿囊、尿囊血管、卵黄囊及周围的胚外中胚层、胚外体腔、血管等包于其中,形成体蒂,此为脐带的前身.随着胚胎的发育,羊膜腔逐渐长大,胚外体腔缩小,脐带日益增长,至胎儿足月时平均长度约50cm,一般在30～70cm 之间,故正常头位分娩脐带至少应有32cm长,若短于30cm 或长于70cm,为脐带过短或脐带过长.在脐带增长过程中,尿囊被包围入脐带后,原来
1 The formation of umbilical cord differentiates mesoderm tissue from the ectoderm of embryo plate early in the embryo, and its dorsal side develops faster than the ventral side, separating the top of amnion from trophoblast. With the extension of neural tube, the embryo protrudes from the amnion , And the end of the embryonic plate mesoderm cells and trophoblast connected to the ventral parcels, the allantoic, allantoic vessels, yolk sac and surrounding extra-embryonic mesoderm, extraembryonic body cavity, blood vessels, etc., which form the body pedicle, This is the predecessor of the umbilical cord.With the development of the embryo, the amniotic cavity gradually grows, the extra-corporeal cavity narrows, the umbilical cord grows to the average length of the fetus when the average length of about 50cm, generally between 30 ~ 70cm, so the normal head childbirth The umbilical cord should be at least 32cm long, if shorter than 30cm or longer than 70cm, the umbilical cord is too short or the umbilical cord is too long.In the process of umbilical cord growth, the allantois is surrounded by the umbilical cord, the original