Embryogenesis and Germ Layer Formation (2C) - MCAT Biological and Biochemical Foundations of Living Systems

Endoderm. Innermost layer develops into internal linings and glands via epithelial folding.

Ectoderm (neural crest). Neural crest cells migrate to form chromaffin cells of the medulla, producing catecholamines.

Ectoderm. Outermost layer differentiates into external and neural tissues via inductive signals.

Rolling of a cell sheet inward over an internal surface. Allows cells to move interiorly along an internal surface, contributing to mesoderm formation.

Inward folding of a cell sheet into the embryo. Creates internal cavities like the archenteron by bending epithelial sheets during layer formation.

A groove where epiblast cells ingress during gastrulation. Defines the embryonic axis and site for mesoderm and endoderm formation in amniotes.

Embedding of the blastocyst into the endometrium. Occurs around day 6-7 post-fertilization, establishing maternal-fetal interface for nutrient exchange.

A solid ball of cells formed after cleavage. Represents compaction of blastomeres before fluid accumulation leads to blastocyst stage.

A hollow ball of cells surrounding a fluid-filled cavity. Forms after cleavage and cavitation, preparing for implantation and gastrulation.

Inner cell mass (embryoblast). Contains pluripotent cells that differentiate into all embryonic tissues during development.

Trophoblast (outer cell layer). Differentiates into syncytiotrophoblast and cytotrophoblast, facilitating implantation and placental formation.

Reorganization forming ectoderm, mesoderm, and endoderm. Establishes the three primary germ layers essential for organogenesis in triploblastic animals.

Fluid accumulation creates a central cavity. Occurs as trophoblast cells secrete fluid, transforming the morula into a blastocyst.

A diploid cell formed by fusion of sperm and oocyte. Results from fertilization, combining genetic material to initiate embryonic development.

A cell produced by cleavage divisions of the zygote. Each is totipotent initially, contributing to the morula through successive cleavages.

Rapid mitotic divisions without overall embryo growth. Divides the zygote into smaller blastomeres while maintaining constant volume until blastula formation.

Individual cells migrate inward from the surface layer. Facilitates individual cell migration to form new layers, as seen in primitive streak gastrulation.

Mesoderm. Middle layer forms supportive and connective tissues through segmentation and differentiation.

The opening of the archenteron to the exterior. Becomes the anus in deuterostomes or mouth in protostomes, connecting archenteron externally.

The primitive gut formed during gastrulation. Develops into the digestive tract lining through gastrulation movements in deuterostomes.

Endoderm. Hepatocytes derive from endodermal foregut diverticulum during organogenesis.

Splitting of one cell sheet into two parallel sheets. Separates cell layers without migration, often forming endoderm from hypoblast in some species.

Notochord. Mesodermal structure secretes signaling molecules like Shh to pattern neural plate formation.

Formation of the neural tube from the neural plate. Involves ectodermal thickening, folding, and closure induced by notochord for CNS development.