Template:Week 4 Embryo Stages and Events table
Week 4 - Human Embryo Stages and Events (GA week 6) | ||
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Embryo Week: Week 1 | Week 2 | Week 3 | Week 4 | Week 5 | Week 6 | Week 7 | Week 8 | Week 9 | ||
Event | ||
Stage 10 | ![]() ![]() neural crest - differentiation at spinal cord level from day 22 until day 26 neural - neural folds begin to fuse near the junction between brain and spinal cord, when neural crest - cells are arising mainly from the neural ectoderm neural crest - trigeminal, facial, and postotic ganglia components visible[1] neural crest - migration of vagal level neural crest cells begins (7-10 somite stage) neural - Brain rostral neural tube forms 3 primary brain vesicles (week 4) respiratory - Week 4 laryngotracheal groove forms on floor foregut. | |
heart - begins to beat in Humans by day 22-23, first functioning embryonic organ formed. | ||
Stage 11 | ![]() thyroid - thyroid median endodermal thickening in the floor of pharynx neural - rostral (or cephalic) neuropore closes within a few hours; closure is bidirectional, it takes place from the dorsal and terminal lips and may occur in two areas simultaneously. The two lips, however, behave differently. Optic ventricle appears | |
Stage 12 | ![]() pituitary - Week 4 hypophysial pouch, Rathke's pouch, diverticulum from roof liver septum transversum forming liver stroma and hepatic diverticulum forming hepatic trabeculae[2] neural - caudal neuropore takes a day to close (closure is approximately at future somitic pair 31/sacral vertebra 2) neural - secondary neurulation begins neural crest - cardiac crest, neural crest from rhombomeres 6 and 7 that migrates to pharyngeal arch 3 and from there the truncus arteriosus[1] neural crest - vagal neural crest enter the foregut (20-25 somite stage) | |
Stage 13 | ![]() telencephalon cavity appears liver epithelial cord proliferation enmeshing stromal capillaries[2] smell Crest comes from the nasal placodes[4] integumentary - 4 weeks simple ectoderm epithelium over mesenchyme integumentary - 1 to 3 months ectoderm - germinative (basal) cell repeated division of generates stratified epithelium; mesoderm - differentiates into connective tissue and blood vessels | |
Note - the day timing of stages is only approximate, system names link to first page of that specific system, and events are based upon the literature cited below. | ||
References
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