313338593组胚课件06留.ppt

General embryology 1 Lei Lei Today’s contents Introduction of embryology Gametogenesis 1st week, ovulation to implantation ★ 2nd week, bilaminar germ disc ★ What is embryology? Embryology is a science that studies the normal development as well as the birth defects of a human being in the maternal uterus. Normal development Takes 38 weeks from fertilization to parturition of a mature fetus. Three periods are divided: 1) Preembryonic period: First 2 weeks, Fertilization to formation of the bilaminar germ disc. 2) Embryonic period: Weeks 3 – 8, Primordial of all major organs develop from the three germ layers. 3) Fetal period: Week 9 – birth. Growth of the organ systems Birth defects The study of the congenital molformations is the Teratology The susceptible period to teratogenic factors generally is the embryonic period (3-8wks), because intensive differentiation occurs in this period. Three Eras of Embryology The Anatomical Tradition (300BC-1870 AD) The Age of Experimental Embryology (1870-1930) The Modern Synthesis (1930-present) Aristotle (384-322 BC) “Father” of Embryology Made observations on chicken and other embryos. Concluded that embryos form gradually and they do not possess adult features until after birth. Epigenesis and Preformation Debate (1700’s) Karl Ernst von Baer (1792-1876) First to observe the mammalian egg. ? Carried out detailed descriptions of a wide variety of embryos. ? Formulated a set of developmental principles. Von Baer’s Embryos Experimental embryology The genetic control of early embryonic development Chapter 1. Gametogenesis Spermatogenesis 1.2 The purpose of gametogenesis Reduction of the number of chromosomes to half by meiosis, which occurs only in germ cell. Alteration of the shape of germ cells for fertilization Abnormal gametes For fertilization to occur, egg and sperm must meet between 2 – 48 hrs after sex. Egg is only fertilizable for 48 hrs. 1.5 Nondisjunction in the meiosis leads to birth defects 1.5.1