Early Embryology: Zygote to Neural Crest

Zygote

Fertilized egg containing genetic material from both parents.

Cleavage

Rapid cell division without growth, resulting in progressively smaller daughter cells.

Morula

A solid ball of small cells formed after several cleavages.

Blastocyst

A developed embryo with a fluid-filled cavity (blastocoel) and cells reorganized to form placental lineage and the inner cell mass.

Trophoblast

The outer cell layer of the blastocyst that contributes to placental formation, enabling maternal nutrient exchange.

Inner Cell Mass

The key embryonic structure within the blastocyst that gives rise to the embryo proper.

Blastocoel

The fluid-filled cavity inside the blastocyst.

Amniotic Cavity

A fluid-filled space that develops after day 8, surrounding the developing embryo to provide a protective environment.

Bilaminar Germ Disc

A two-layer embryonic structure formed by the epiblast and hypoblast, preceding gastrulation.

Epiblast

The outer layer of the bilaminar germ disc, eventually facing the amniotic cavity.

Hypoblast

The inner layer of the bilaminar germ disc, lining the yolk sac.

Primitive Streak

A structure that forms and enables cell migrations, initiating germ layer formation.

Gastrulation

The process by which a trilaminar embryonic disk forms from the bilaminar disc, establishing the three primary germ layers.

Trilaminar Germ Disc

The embryonic disc consisting of three primary germ layers: ectoderm, mesoderm, and endoderm.

Ectoderm

The outermost germ layer, which gives rise to the nervous system and epidermis.

Mesoderm

The middle germ layer, which gives rise to muscle, bone, blood, connective tissues, kidneys, and gonads.

Endoderm

The innermost germ layer, which forms the epithelium of the gut and associated organs (e.g., digestive and respiratory tracts).

Notochord

A mesodermal structure providing inductive signals to pattern surrounding tissues and crucial for neural tube formation and axial skeleton development.

Neural Crest

Pluripotent cells that contribute to craniofacial skeleton, peripheral nervous system components, and other derivatives.

Induction

Chemical signaling between tissues where one tissue triggers subsequent differentiation and organogenesis in another.