Title: Embryo Development - A Development process of Fetus - Week by Week
Headings: Embryo Development
Embryo Development
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Content: Ectoderm- nervous system, brain, spinal cord, epidermis, hair, nails, etc. Mesoderm- connective tissue, muscles, circulatory system, notochord, bone, kidney, gonads
Endoderm- internal organs, stomach, liver, pancreas, bladder, lung, gut lining
Weeks after Fertilization
Embryonic Development
Week Three
Gastrulation and formation of three germinal layers. Neurulation follows gastrulation. Notochord is formed
Week Four
The heart is the first organ to start functioning. The heart starts beating. Arm buds and optic pits become visible
Week Five
Size ~ 4 mm. Starts becoming C-shape, inner ear starts developing, pharyngeal arches develop, liver, pancreas, spleen and gall bladder start developing
Week Six
Size ~ 8 mm. Development of eyes and nose, leg buds and hand as flat paddles appear, stomach and kidney precursors start developing
Week Seven
Size ~ 13 mm. Lungs and lymphatic system and primary sex organs start developing, arms and legs lengthen and digits start appearing
Week Eight
Size ~ 20 mm. External ear starts appearing, nipples and hair follicles start developing, most of the organs start developing by this time
To sum up, the heart is the first organ to start working.