胚胎学总论中医健康理念.pdf

第20 章 胚胎学总论 ——人体胚胎发生 CHAPTER 20 GENENRAL EMBRYOLOGY ——The Embryonic Development of Human Body KYEY POINTS  Gametogenesis  Fertilization  Development in pre-embryonic period  Development in embryonic period  Development in fetal period  Fetal membrane and placenta  Twins, multiple birth and conjoined twins 一、 配子发生和受精 GAMETOGENESIS AND FERTILIZATION OUTLINE: The fertilization is a process by which the male and female gametes unite to give rise to the zygote. Before fertilization both male and female germ cells undergo a lot of changes involving the chromosome as well as the cytoplasm. The mature process of the germ cells is known as gametogenesis. The gametogenesis is chiefly accomplished by two specialized divisions, known as meiotic or maturation divisions, by means of which the number of chromosome is reduced by half, from 46 to 23. The male germ cell, initially large and round, loses almost all of its cytoplasm and develops a head, neck and tail (a tadpole-like structure). The female germ cell, on the contrary, increases in the amount of cytoplasm. Fertilization is an important biological process by which the zygote restores the normal diploid number of chromosome, determines the genetic sex of the new individual, and initiates cleavage. (一)配子发生Gametogenesis 258 （二）受精Fertilization OVULATION The process by means of which the oocyte with its cumulus oophorus cells is discharged from the ovary is known as ovulation. In the meantime the first meiotic division is complete, and the secondary oocyte starts its secon