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2021 BCE
Week 1
Egg and Sperm meet to form a zygote. Cell division occurs to form 2 blastomeres that divide into a morula. Free floating blastocysts reaches the uterus, attaching to uterine wall. This initiates the first localized transformation of uterine endometrium into decidua. -
2021 BCE
Week 2
In the conceptus, blastocysts explode rapid differentian into extra-embryonic, embryonic tissues and proliferation. Release of the hCG to initiate maternal changes, this stops the menstrual cycle. -
2021 BCE
Week 3
During week 3, trophoblast cells invade uterine wall in early placentation. The site of the inner cell mass determines the embryonic pole of the blastocyst. The opposite side of the blastocyst becomes the abembryonic pole. -
2021 BCE
Week 4
This is the beginning of organogenesis. Sensory placodes and limb bods start to appear of the surface. Within the embryo, it starts to fold. Certain organs start to form. -
2021 BCE
Week 5
The embryo is made out of three layers, the ectoderm, mesoderm, and endoderm. Embryo starts to form skin, nervous system, and the ears. -
2021 BCE
Week 6
A brain and spinal cord develop because of the neural tube. The small buds transform into arms and the heart begins to beat. -
2021 BCE
Week 7
The pancreas and respiratory system start to develop. Pancreas secretion levels increase and the liver expands. Some facial structures start to appear. -
2021 BCE
Week 8
90% of the adult anatomical structures are formed. Arm and leg limbs are starting to grow with fingers and toes underneath. The eyes are starting to show pigment. However it is too soon to identify the gender.