Early Human Embryonic Development Quiz

Fertilization and Early Development

• The result of the union of sperm and egg is fertilization, which mostly occurs in the ampulla of the fallopian tube.
• After reaching the 8-cell stage, morula cells undergo compaction, resulting in a tight cluster of cells.

Developmental Stages

• Cells at the morula stage can develop into various cell types, including trophectoderm, embryoblast, and primitive endoderm.
• The blastula/blastocyst stage is characterized by the filling of a fluid-filled compartment called the blastocoel, which helps to establish the embryonic poles.
• The result of the blastula/blastocyst stage in human development is the formation of a hollow ball of cells that can implant into the uterine lining.

Pre-implantation Genetic Screening

• The outcome of sampling for pre-implantation genetic screening in IVF clinic samples is the identification of euploid embryos, which can improve IVF success rates.

Maternal to Zygotic Transition

• The maternal to zygotic transition starts in humans around the 4- to 8-cell stage, during which the embryo begins to take control of its own development.

IVF Success

• IVF success to live birth is about 2-fold more successful using the blastocyst stage than the morula stage because the blastocyst stage allows for better selection of euploid embryos.

Trophoblasts and Blastocoel

• Trophoblasts play a crucial role in the developing embryo, giving rise to the placenta and other supporting tissues.
• The fluid-filled compartment called the blastocoel helps to establish the embryonic poles and gives rise to the amniotic cavity.

Apoptosis and Euploid Selection

• Excessive apoptosis during the selection for euploid cells in the developing embryo can result in embryo fragmentation and decreased IVF success.

Gastrulation

• The formation of the primitive streak on the dorsal side of the developing embryo marks the beginning of gastrulation, during which the embryo undergoes a series of complex cellular movements.
• The primitive streak gives rise to the endoderm, which is one of the three primary germ layers.

Amniotic Cavity

• The amniotic cavity, which forms from the blastocoel, provides a protective environment for the developing embryo and eventually forms the amniotic sac.