Principles

Mother's RNA activates gap genes or pair genes (differentialy based on location i guess activating homeobox genes which produce trasncription factors that activate the realizor genes. homeoboxe are differentially activated in a caudal cephalic axis.

The embryoblasts of the blastocyst (outer ring is trophoblast - begin secreting hcg in week 1)
differentiate into a bilayered disc, 1 layer of epiblast one of hypoblast during week 2 (wwek 2 = 2 layers) amnion (an inner layer of the chorion, from which yolk sac will eventually develop) developed at beggining of this week.

Forms in week 3 from the epiblasts, its a radius of the disc and defines ant-post axis. epiblasts migrate inferior through the primitve streak to become a middle cell layer ie mesoderm. neural plate forms next to primitive streak. notochord forms below it from the mesoderm --> induces neural plate formation in fact. becomes uclei pulposus.
(week 3 = 3 layers forms)

Weeks 3 - 8 neural tube forms and closes, organogenissi, extremely susceptible to teratogens here. before this its all or nothing, after the organ will be there but may be missized or functioning

Heart beats, limb buds form (week 4 = 4 chambers, 4 limbs)

Begins week 8, looks liek a fetus and moves.

Genetalia can be sex distinguished. neural tube differentiates to be recognizable as spinal cord, sensory (dorsal horn) called alar, motor called basilar.

Mostly obvious ex surface ectoderm forms adenohyphisis, sensory organs of the ear. remeber aslo it envaginates so forms the oral cavity lining and some of the ass hole.
neural crest non obvious: pia and arachnoid and skullbones incl odontoblasts and the aortico-pulmonary septum, melanocytes and parafollicular of the thyroid
endoderm: remeber the gut gives off the accesory gi organs as well as the lungs, thyroid and parathyroid (folic cells)
every other organ is prety much mesoderm

Happens in the embryonic period, so all the fetal misdevlopments look "intrinsic"

Occurs in fetal period, so fuck up can be identified with the "extrinsic" insult

Means the primordial cell for that tissue never formed

A means lack of proper proliferation of primordial cell resulted in no organ, hypo means resulted in deificent organ.

Leading cause of birth defects and retardation, microcephaly, holoprosencephaly (prosen is the forebrain of embryo, holo for whole ie doesnt develop two hemispheres) limb dislocations, heart/lung fistulas, asian/black/thinupperlip(belgian) face

Renal damge in fetus

Ie add a methyl group and extra fingers too!