Development of the embryo

End of 2nd Week:
1. The amnion (group of cells in Trophoblast the becomes amniotic sac) and chonion (group of cells the becomes the foetal part of the placenta ) membranes emerge from the Trophoblast (membrane of the blastocyst that eventually divide into amnion & chonion) & surround developing embryo
2. The inner cell mass seperates into 3 layers, the ectoderm, endoderm & mesoderm, which becomes the body parts & organs
3rd Week:
1. The foundations of the brain, spinal chord & nervous system develops
2. Rudimentary blood cells & blood vessels evolve
3. The heart develops, first as a tube, then as a chambered pump
4. Heart begins to beat at the end of the 3rd week
4th Week:
1. A system for digesting food & kidney-like structures form
2. Arm & leg buds appear
3. Eyes & ears begin to take shape
4. The formation of major veins & arteries are comlpeted
5. The vertebrae of the spine becomes more visible
6. Nerves begin to form simple structures
5th Week:
1. Umbilical chord, linking the embryo to the placenta, forms
2. Bronchial buds, which becomes lungs, develop
3. Masses (that become muscles) appear in the head, trunk & limbs
6th Week:
1. The head predominates in size
2. The outer ear takes shape
3. Lower jaw is complete, upper jaw begins to form
4. Main parts of the brain (hindbrain, midbrain & forebrain) becomes distinct
7th Week:
1. Face & neck begin to take definite form
2. Eyelids take shape
3. Stomach takes final shape and position
4. Muscles take final shape & relationships
5. Brain develops 1000s of nerve cells per second
6. A valve develops in the heart to sepirate upper & lower parts
8th Week:
1. Neck becomes distinct & head elevates
2. Body assumes more rounded appearance
3. Embryo about 2cm in length
4. Capable of some movement & responds to stimuli around the mouth

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Development of the embryo

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	Created by Zeneatha Jònsson over 9 years ago