Embryology: Early Development

In which specific part of the uterine tube does fertilization typically occur?

The ampulla of the uterine tube.

What is the name of the solid ball of 16 to 32 cells that forms approximately 3 to 4 days after fertilization?

Morula.

Which part of the blastocyst is responsible for forming the embryo proper?

The inner cell mass (or embryoblast).

What biological process defines the transition from a bilaminar disc to a trilaminar disc?

Gastrulation.

The central nervous system and the epidermis are derived from which embryonic germ layer?

Ectoderm.

The epithelial lining of the respiratory and digestive systems is primarily derived from which germ layer?

Endoderm.

Why do the individual cells (blastomeres) become smaller with each division during the cleavage stage?

The zygote is contained within the rigid, non-expanding zona pellucida.

On approximately which day post-fertilization does the blastocyst begin the process of implantation?

Day 6.

Which layer of the trophoblast is multinucleated, lacks distinct cell boundaries, and invades the maternal endometrium?

Syncytiotrophoblast.

The appearance of which structure at the caudal end of the epiblast marks the formal beginning of gastrulation?

The primitive streak.