Anatomy and Physiology II Practice Test

What is the name of the solid ball of cells that forms when the developing egg reaches the uterus?

1. Blastocyst

2. Embryo

3. Morula

4. Zygote

The correct answer is: Blastocyst

The correct answer, referring to the solid ball of cells that forms when the developing egg reaches the uterus, is known as the blastocyst. This structure emerges after several divisions of the zygote, which initially begins as a single fertilized egg cell. As the zygote travels down the fallopian tube toward the uterus, it undergoes a series of mitotic divisions, becoming a morula, which is a solid ball of cells that resembles a mulberry. Once the morula continues to develop and fluid begins to fill its internal cavity, it transforms into a blastocyst. This stage is crucial for implantation into the uterine wall, where the blastocyst differentiates into the various cell types needed for further development into an embryo. The blastocyst consists of an outer layer of cells, which will become part of the placenta, and an inner cell mass that will develop into the embryo itself. Understanding this developmental process emphasizes the importance of the blastocyst stage in early pregnancy, as it marks a key transition from a mere collection of cells to a structure that will implant and support the future growth of the embryo.