Name Brief description/function When is it formed? What is it derived from? What does it give rise to? Additional notes Blastocyst Mammalian version o

Blastocyst

Mammalian version of blastula; hollow ball of cells that have not yet differentiated into germ layers.

When is the blastocyst formed?

Days 1-7 (prior to implantation and gastrulation).

What is the blastocyst derived from?

Zygote.

What does the blastocyst give rise to?

The embryo.

Trophoblast

Outer epithelium of blastocyst; initiates implantation.

When is the trophoblast formed?

Days 1-7 (prior to implantation and gastrulation).

What is the trophoblast derived from?

Outer layer of blastocyst cells.

What does the trophoblast give rise to?

The placenta.

Epiblast

During gastrulation, epiblast cells form all three germ layers.

When is the epiblast formed?

Around implantation time (7 days after fertilization).

What is the epiblast derived from?

Inner layer of blastocyst cells.

What does the epiblast give rise to?

The 3 primary germ layers.

Hypoblast

Helps orient embryo and primitive streak leading to/during gastrulation.

When is the hypoblast formed?

Around implantation time (7 days after fertilization).

What is the hypoblast derived from?

Inner layer of blastocyst cells.

What does the hypoblast give rise to?

The yolk sac, the allantois, and the embryonic endoderm.

Extraembryonic membranes

Chorion; allantois; amnion; yolk sac.

When are extraembryonic membranes formed?

Around implantation time (7 days after fertilization).

What do trophoblast, epiblast, and endometrial tissue form?

The 'life support' system of the embryo.

Placenta

Mediates gas exchange, nutrient exchange, waste disposal between embryo and mother.

When is the placenta formed?

After implantation (10-11 days after fertilization).

What is the placenta derived from?

Trophoblast, epiblast, and endometrial tissue.

What does the placenta provide?

Gas exchange and nutrients.