2. 2nd week of
development

3. • Introduction
• Developmental changes
CONTENTS:

4. INTRODUCTION:
Starts from day 8th to day 13th day
It is about the blastocyst implantation and its
differentiation
Formation of biliminar disc and germ layers that
ultimately forms the future tissues and organs
It can be vary from person to person

5. DEVELOPMENTAL CHANGES:
• DAY 8:
Blastocyst partially embedded in the uterine endometrium
It is differenciated into two:
• Outer trophoblast
• Inner cell mass
Trophoblast is further divided into two layers
• Outer cytotrophoblast
• Inner syncytiotropoblast (responsible for the secretion of HCG)

6. CONTINUE:
Inner cell mass also differenciated into two layers:
• Layer of cuboidal cells called “hypoblast”
• Layer of columnar cells called “epiblast”
These two layers togather form a disc called “ bilaminar embryonic
disc”
Formation of cavity between he epiblast and cytotrophoblast caalled
“embryonic cavity”

7. CONTINUE:
Cells of hypoblast migrates inward and forms the extra ceolomic
membrane
It forms the wall of yolk cell
Adjacent to the side of implantation endometrial stromais present
which is edamatous and vascular
Tortuaos glands secrets abundant glycogen and mucous

9. DAY 9, 10 and 11)
Blastocyst is more deeply embided in the endometrium
Growth of cytotrophoblast and syncytiotropoblast become quicker
Small holes called “lacunae” start to develop in the
syncytiotrophoblast also called lacunar stage

10. • DAY 12 and 13:
Blastocyst is completely embedded in the endometrium
Growth of lacunae stops and form large interconnecting spaces called
lacunar networks
Capillaries sorrounding the endometrium dilates and spaces are form
called called maternal sinusoids
Enzymes present in the lacunar spaces allows the blood from the
capillaries and uterine glands to enter the lacunar network called
uteroplacental circulation

11. CONTINUE
Cells starts to form between the cytotrophoblast and the yolk sac
called “extra embryonic mesoderm”
Cavity is form between these cells called “chorionic cavity”
Large portion of extra celomoic cavity pintched of forming smaller
cavity called secondary yolk sac
At the end of the second week bilaminar embryonic disc connect
with the trophoblast called “connecting stalk (the future umblical
cord)

13. SUMMARY:
• Starts from from day 8-13
• Implantation of blastocyst
• Secreation of HCG
• Diferenciation of trophoblast
• Formation of germ layers
• Development of amniotic cavity and yolk sac
• Initiation of utero-placental circulation

14. REFERENCES:
• Langman’s medical embryology
• www.embryo.med.unsw.edu.au
• www.kenhub.com