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12 Cards in this Set
- Front
- Back
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when does gastrulation start to happen?
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in 3rd week - by the end of the 2nd week, blastocyst is completely embedded.
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how does gastrulation begins?
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it begins with the formation of primitive streak on the caudal surface of epiblast of embryonic disc.
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what are the type of cells of the bilaminar germ disc?
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epiblast: columnar cells.
hypoblast: cuboidal cells. |
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how's the mesodermal layer formed?
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the cells from hypoblast proliferate and lies between the germ layers known as the mesodermal layer - nw the inner cell mass became trilaminar germ disc.
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how does the primitive node (PN), primitive pit (PP)formed?
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-epiblast migrate & differentiate in the cranial end of primitive streak to form PN.
-in PN, cells proliferate forming PP. -cells from deep surface of primitive streak leave & form Intra Embryonic mesenchyme until 4th week. |
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how does the notochordal process develop?
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-some mesenchyma cells migrate cranially from PN and PP.
-form median cellular cord (notochordal process -NP) -soon a notochordal canal develops. -NP grows cranially between ecto n endo. -until it reach prochordal plate, prolongation stopped. |
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what is notochord?
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-the notochord is a cellular rod that develops by transformaion of the NP.
-it defines the primordial axis of embryo and rigidity. |
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does the notochord helps for development of axial skeleton? how?
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-yes.
-later the notochord becomes flattened and forms notochordal plate. -it become the future site of vertebral bodies. -remnants of the notochord is the nucleus pulposis of intervertebral discs. |
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how does neural tube (NT) forms?
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-neurulation.
-thickening of embryonic ectoderm cranial to primitive node. -become neural groove and neural folds. -fusion of neural folds: NT. -separate from the surface ectoderm. -NT is the primordium of (give rise to) CNS. |
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how does central canal connect with the amniotic cavity?
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thru anterior and posterior pores.
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what happen to anterior and pore during 4th week?
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anterior pore closes n become lamina terminalis.
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what happen if anterior and posterior pore fail to close in 4th week?
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anterior pore failure: anencephaly.
posterior pore failure: spina bifida. |
