Early embryogenesis

<p>Jun 13, 2015 03:33 PM</p>

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this is a must-see from Khan Academy (? identity of lecturer).

This is a marvel of clarity &nbsp;(for a topic that I struggled with as a med student.)</p>

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zygote (fertilized egg) &nbsp;then cell division with no growth into

morula &nbsp;32 cells inside zona pellucida. &nbsp;then cells compact &nbsp;(compaction)</p>

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cells on the outside are trophoblasts and cells on inside are embryoblasts

(those are the inner cell mass) &nbsp;and empty &nbsp;blastocoel</p>

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that is a blastocyst.</p>

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inner cell mass forms evreything! &nbsp;it differentiates into</p>

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epiblasts and hypoblasts. &nbsp;those form a pancake</p>

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and primitive streak forms on top &nbsp;(like syrup on top) &nbsp;&nbsp;the start of gastrulation</p>

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cells of epiblast burrow in thru primitive streak &nbsp;to form</p>

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3 layers &nbsp;trilmainar disk &nbsp;of germ layers: &nbsp;ectoderm, mesoderm, endoderm:

the process is called gastrulation.</p>

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next step is neurulation;</p>

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then notochord forms in the mesoderm &nbsp;(part of interverteb disk); &nbsp;it induces change in ectoderm.</p>

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it induces the neural plate. &nbsp;those cells dive in toward notochord... to form neural tube.</p>

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and cells break off to form &nbsp;neural crest cells.</p>

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