Carnegie stage 3
Human Blastocyst "hatching" from zona pellucida, in early Embryonic Development designated as Carnegie stage 3. Blastocyst is too the right of image and Zona pellucida is shown to the left of the image. Note: the small opening in the zona pellucida through which the blastocyst is hatching the flattened trophoblast cells forming the outer cell layer of the blastocyst the inner cell mass shown in the centre of the image and on the left-hand wall of the blastocyst the blastocoel forming a large fluid-filled space within the blastocyst
Image source: Klimanskaya I, Chung Y, Becker S, Lu SJ, Lanza R. Human embryonic stem cell lines derived from single blastomeres. Nature. 2006 Aug 23 PMID:16929302
Facts: Week 1, 4 - 5 days, size 0.1-0.2 mm
Features: zona pellucida, trophoblast shell, inner cell mass, blastoceol
About Carnegie Stages
Carnegie stages are named after the famous US Institute which began collecting and classifying embryos in the early 1900's. Stages are based on the external and/or internal morphological development of the embryo, and are not directly dependent on either age or size. The human embryonic period proper is divided into 23 Carnegie stages. Carnegie stages are based on the external and/or internal morphological development of the embryo, and are not directly dependent on either age or size. Criteria beyond morphological features include age in days, number of somites present, and embryonic length.
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