chorion and amnion

 Chorion and Chorionic Villi

Chorion is outermost fetal membrane around embryo.

After implantation trophoblast differentiated into; 

1. Outer layer Syncytitrophoblast

2. Inner layer Cytotrophoblast (Langhan’s layer)

Chorion layer made up of trophoblast and mesoderm.

Chorion villi surround developing ovum.

Villi overlying decidua basalis continue to grow and expand called chorion frondosum and form placenta.

Mesodermal tissue (connecting stalk) connects inner cell mass to chorion and will form umbilical cord later on.

Development of Inner Cell Mass

Development of inner cell mass differentiated into;

1. Amnion layer of embryo cell

2. Umbilical cord

3. Foetus

After implantation, 2 cavity appear in inner cell mass.

1. Amniotic cavity/ amniotic sac contains amniotic fluid

Amnion membrane forming fluid filled cavity (amniotic sac that enclose the embryo).

2. Yolk sac

Before placenta form, yolk cell provide nutrition and gas exchange between mother and developing embryo.

Inner Cell Mass 

Inner cell mass known as embryoblast.

Embryoblast development of embryo embryonic stem cell (ESCs) form bilaminar embryonic disc that differentiated into;

1. Epiblast

External layer

Primary ectoderm

Form amnion that surround amniotic cavity.

2. Hypoblast

Internal layer

Primary endoderm

Form yolk sac

Form amniotic cavity.

Note; Connective stalk form umbilical cord.