Help with Developmental Stages and Events - Anatomy

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Question

Which developmental stage results in the rise of the three germ layers?

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Answer

After fertilization and the formation of a zygote, the developing organism undergoes several rounds of cell division known as cleavage. During this period the cells divide but do not grow in size, resulting in a dense cell mass. The morula is formed during this portion of development.

Following cleavage, the cell develops an inner cell mass and trophoblast, or outer layer, before implantation into the uterus. At this stage, the organism is considered a blastocyst.

Soon after implantation, cells begin to differentiate into the three germ layers through a process known as gastrulation. The resulting organism is considered a gastrula.

Gastrulation is quickly followed by development of the neural crest and preliminary nervous tissue, known as neurulation. The organism is then considered a neurula.

Note that the organism can be considered an embryo at any point from the first cleavage division to approximately the eighth week of development.

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