1. General embryology Jun Zhou ( 周俊） School of Medicine, Zhejiang University 20131223 Langman’s Medical Embryology, 9th Ed

2. Fertilization 14 days Onset of last M.C. 266 days 280 days  a science which study the processes and regulations of development of human fetus.(from 1 cell (zygote) to (5-7) x10 12 cells)  In general the length of pregnancy is considered to be 280 days or 40 weeks after the onset of the last menstruation, or more accurately, 266 days or 38 weeks after fertilization. Labor

3. Preembryonic period: before 2 weeks Embryonic period: 3-8 weeks Fetal period: after 9 weeks Total 38 weeks:

4. Embryonic period: 3-8 weeks Fetal period: after 9 weeks Preembryonic period: before 2 weeks

5. Fertilization  Definition: the process by which the male and female gametes(sperm and ovum) unite to give rise to zygote  place: in the ampullary region of the oviduct

6. conditions: 1) maturation of oocyte 2) maturation of spermatozoa

7. 3) capacitation and acrosome reaction of spermatozoa: R5 capacitation factor: secreted by epi. cells of oviduct, capacity of releasing acrosome enzymes 4) quality and quantity of spermatozoa: 2-6 ml, 100,000,000/ml, 30%; or capacity for mobile< 70% 5) meeting of sperm and ovum within 24 hrs

8. Processes of fertilization: Phase I –penetrate the corona radiata, acrosomal release Phase II –ZP with receptors – zona pellucida spongy – the release of local enzymes Phase III –Success formation of zygote

9. Entry – response 1)Cortical or zona reactions - Compaction - impermeable to more sperm 2)Oocyte finishes 2 nd meiotic division 3)Female /Male pronucleus 4)Metabolic activation of the egg Results of fertilization –Diploid –Genetic sex –Cleavage

10. Cleavage Mitosis and cytoplasmic division Blastula - blastomeres Morula –inner cell mass embryoblast –outer cell rim trophoblasts Blastocyst –Blastocoele –The cells of morula secrete fluid –Zona pellucide disappears

11. Puberty – menstruation (28 days) Hormonal regulation –GnRH –FSH –LH Granulosa/theca cells –Estrogens –Progesterones The endometrium of the uterus is in the secretory phase Uterus at Time of Implantation

12. Implantation - Passage through the uterine tube Day 5 –Day 11 Uterus Orientation of implantation Location - ant or post, fundus Trophoblasts overlying the embryoblast pole attach to the endometrium, erosion into deep uterine vessels

13. Processes zona pellucide disappear → polar trophoblast touch the endometrium→secrete enzymes →dissolve the endometrium → embedded into endometrium → coagulation plug seal the space

14. Implantation site –Normal:ant or post wall of the uterus –Abnormal –Tubal –Internal os of the cervix –Ovarian –Abdominal

15. endometrium → decidua: - decidua basalis -decidua capsularis -decidua parietalis conditions: - endometrium is in secretory phase -morula reach the cavity of uterus on time -zona pellucide disappears in time

16. Implantation - sinks deeper The outer cell layer –Trophoblasts cytotrophoblasts syncytiotrophoblasts Inner cell mass (embryoblast) –Fluid collection – amnion –Epiblasts & hypoblasts Bilaminar Germ Disc (Second week of development)

17. Week two – Day 9-12 Implantation –Covered the endometrium- fibrin plug –Complete – slight bulge Trophoblasts –Vacuoles within syncytiotrophoblasts- fuse and form lacunar networks –Uteroplacental circ Extra-Embryonic Mesoderm –btwn troph & cavity –Somatic/splanchnic

18. Week 2 – Day 13-14 Trophoblasts –Primary villi Yolk sac –Primary to seconday –Chorionic plate –Connecting stalk

19. The Bilaminar Embryo Disc btwn –Amnion –Yolk sac Bilaminar disc –Epiblasts –Hypoblasts

20. End of the Week of Twos 2 major cell masses –Trophoblasts –Inner cell mass Trophoblasts –Cytotrophoblasts –Syncytiotrophoblasts Embryonic Cavities –Amniotic cavity –Yolk sac Germ Disc –Epiblasts –Hypoblasts

21. OBJECTIVES 1.The definition of Embryology 2.The major phases of fertilization and the site where fertilization typically occurs 3.Endometrial changes that enable implantation and the hormones that modulate this change 4.Normal sites of implanation and the most abnormal sites 5.Morphologic changes in the zygote that occur enroute to the uterus 6.The development roles of the inner cell mass and the outer cell mass 7.Bilaminar germ discs