Embryionic development at 2nd week of intrauterine life.

1. DAY 13 Shlok Pushpesh Mathur

2. BEFORE..
Sinusoids
Uteroplacental circulation
Extra embryonic mesoderm
Chorionic cavity
Extraembryonic splancnic (somatic)
mesoderm

3. DURING 13TH DAY..
Primary villi
Secondary yolk sac
Exocoelomic cyst
Chorionic cavity
Chorionic plate
Connective stalk

4. PRIMARY VILLI..
Cells of the cytotrophoblast proliferate
locally and penetrate into the
synctiotrophoblast, forming cellular
collumns surrounded by syncytium.
Cellular collumns with the syncytial
coverings are known as Primary Villi.

5. SECONDARY YOLK
SAC..
The hypoblast produces additional cells
that migrate along the inside of the
exocoelomic membrane.
These cells proliferate and gradually form
a new cavity within the exocoelomic
cavity.
This new cavity is known as the secondary
yolk sac or Definative yolk Sac.

6. EXOCOELOMIC
CYST..
The Secondary yolk sac is much smaller
than the original exocoelomic cavity, or
primitive yolk sac.
During its formation, large portions of
exocoelomic cavity are pinched off.
These portions are represented by
Exoloelomic cysts, which are often found
in the extraembryonic coelom or chorionic
cavity.

7. CHORIONIC
CAVITY..
The extraembryonic coelom expands and
forms a large cavity, the chorionic cavity.

8. CHORIONIC
PLATE..
The extraembryonic mesoderm lining of
the cytotrophoblast is then known as the
Chorionic plate.

9. CONNECTIVE
STALK..
The only place where extraembryonic
mesoderm traverses the chorionic cavity
is in the connective stalk.
With development of blood vessels, the
stalk becomes the umblical cord.

10. THANK YOU!!! Doubt?