1. General embryology Langman’s Medical Embryology, 13th Ed Jun Zhou (周俊）
School of Medicine, Zhejiang University

2. OBJECTIVES The definition of Embryology: 3 periods, total 38/40 weeks
3 phases of fertilization, normal site
Normal sites of implantation and the most abnormal sites
The formation of 2 cells stage, morula, blastocyst
Bilaminar germ discs- epiblast & hypoblast
Trilaminar germ discs
The formation and derivatives of ectoderm, mesoderm and endoderm.
The components of fetal membrane and their functions.
Structure and function of placenta.
Birth defects

3. a science which study the processes and regulations of development of human fetus.(from 1 cell (zygote) to (5-7) x1012 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.
Onset of last M.C.
Fertilization
266 days
14 days
Labor
280 days

4. Onset of M.C.
Ovulation

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

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

7. 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

8. Prerequisite for fertilization:
1)  maturation of oocyte
2)  maturation of spermatozoa
3)  capacitation and acrosome reaction of spermatozoa:
capacitation factor: secreted by epi. cells of oviduct, capacity of releasing acrosome enzymes
4) quality and quantity of spermatozoa:
5)  meeting of sperm and ovum within 24 hrs

9. Oocyte maturation Primordial  primary Zona pellucida
Antrum – secondary
Cumulus oophorus
Secondary oocyte – h before ovulation, polar body

10. Spermatogenesis Germ cells dormant until puberty
At puberty become mitotically active
sertoli cells, nutrition, protection and mechanical support
Unlike oogenesis, 4 sperms per clone

11. 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

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

13. Cleavage Mitosis and cytoplasmic division 2 cells stage (30 hr)
Morula (72 hr)
12-16 cells
Blastocyst ( Day 4-5)(No ZP)
Blastocoele
Inner cell mass
Trophoblasts

14. Blastocyst
trophoblasts
blastocoele
inner cell mass

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

16. -Passage through the uterine tube
Implantation
-Passage through the uterine tube
Day 5 –Day 11 Uterus
Orientation of implantation
- anterior or posterior, fundus
Trophoblasts (overlying the inner cell mass) attach to the endometrium, begin to invade.

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

18. Implantation site Normal: anterior or posterior wall of the uterus
Abnormal
Tubal (most common)
Ovarian
Abdominal
Internal os of the cervix

19. Endometrium →decidua: -Decidua basalis
-Decidua capsularis
-Decidua parietalis
Prerequisite:
-Endometrium is in secretory phase
-Morula/blastocyst reach the cavity of uterus on time
-Zona pellucide disappears in time

20. (Second week of development)
Bilaminar Germ Disc
(Second week of development)
Implantation - sinks deeper
The outer cell layer
Trophoblasts
Cytotrophoblasts
Syncytiotrophoblasts
(Syncytium)
Inner cell mass
Fluid collection – amnion

21. Week two – Day 9-12 Implantation Complete – a slight bulge
Trophoblasts
Vacuoles within syncytiotrophoblasts- fuse and form lacunar networks
Establish Uteroplacental circulation
Primary yolk sac
Extra-Embryonic Mesoderm
btwn troph & cavity

22. Week 2 – Day 13-14
Yolk sac
Primary to seconday
Connecting stalk

23. The Bilaminar Embryo By the end of week 2 Disc btwn
Amnion
Yolk sac
Bilaminar germ disc
Epiblasts (bottom of amnion)
Hypoblasts (roof of yolk sac)

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

25. Happy New Year!