Question

Sort the stages in the order they appear during the embryonic development in humans.

• A. Foetus
• B. Embryo
• C. Morula
• D. Blastocyst
• E. Zygote

Answer 1

The fusion of the male and female gamete gives rise to a diploid single cell called zygote. Cleavage or mitotic division starts in the ampullary-isthmic junction and the zygote starts moving towards the uterus. The daughter cells formed by mitotic cleavage of the zygote is called blastomeres and they clump together. The aggregate of 8-16 blastomeres is called morula.
Morula further divides to form blastocyst and moves further towards the uterus.
Blastomeres in blastocyst are arranged into 1. an outer layer of cells called trophoblast. 2. an inner group of cells attached to the trophoblast called the inner cell mass
The trophoblast attaches to the endometrium while the inner cell mass develops into the embryo.
The embryo is called a foetus from the 11th week of gestation.