Early Human Development Flashcards

Flashcards on Early Human Development

Compaction

The flattening and adhering of blastomeres to one another tightly around the 8-16 cell stage.

Compaction Importance

The first differentiation event in the embryo, limiting cell fates to two pathways.

Blastocoel

A fluid-filled cavity that forms within the morula around day 5 of development.

Inner Cell Mass (ICM)

Cluster of cells at one side of the blastocoel, also called the embryoblast, becomes the embryo; cells are pluripotent.

Trophoblast

Single layer of epithelial cells surrounding the blastocyst, forms extraembryonic tissues (placenta); bipotential.

"Hatching"

Occurs around day 5 when the blastocyst emerges from the zona pellucida.

Zona Pellucida Function

Prevents premature adhesion to the oviduct wall and implantation too soon.

Ectopic Pregnancy

Embryo implants outside the uterus, often in the oviduct, and is not a viable pregnancy.

Bilaminar Germ Disc

The two-layered embryoblast, consisting of the epiblast and hypoblast.

Epiblast

External layer of cells formed from the inner cell mass.

Hypoblast

Internal layer of cells formed from the inner cell mass.

Syncytiotrophoblast

Actively invades the endometrium.

Cytotrophoblast

Divides to create more syncytiotrophoblast cells.

Primary Yolk Sac

Formed by hypoblast cells migrating to line the blastocoel cavity.

Amniotic cavity

The cavity formed between epiblast cells that gets separated from the cytotrophoblast by amnioblasts.

Extraembryonic Endoderm

Also known as Heuser’s membrane, it lines the blastocoel cavity.

Extraembryonic Mesoderm

Formed by cells migrating from the epiblast between Heuser’s membrane and the cytotrophoblast.

Chorionic Cavity

Cavity formed when the extraembryonic mesodermal cells split into two layers.

Definitive/Secondary Yolk sac

Formed by hypoblast cells pushing the primary yolk sac away from the embryo.

Connecting Stalk

Connects the embryo proper to the chorion.

Extraembryonic mesoderm

The first site of hematopoiesis where primitive endothelial and blood cells form blood islands.

Syncytiotrophoblast

Specialized cells in the trophoblast that actively invade the endometrium during implantation.

Cytotrophoblast

Cells that divide to create more syncytiotrophoblast.