Embryo Development Embryonic Period 3 WEEKS The beginnings of the respiratory, digestive, circulatory, nervous and excretory systems are formed. The heartbeat starts.
4 WEEKS The beginnings of the intestine, liver, kidney and lung are formed. The muscular system, spine and the neural tube develop. Neural tube is completed.
5 WEEKS Organs and systems start to form, as do parts of the brain. The umbilical cord appears. The upper lip and nasal cavity are formed, as are the beginnings of the extremities.
6 WEEKS The brain and its divisions form. The formation of the placenta and the muscles of the face begin. The beginning of the hands and fingers form.
7 WEEKS The uteroplacental circulation starts. The upper limbs are developed. The eyes and ear canals start to form.
8 WEEKS The heart, lungs, brain, urinary and reproductive systems are formed. Eyes, eyelids, nose, ears and lips are developed.
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