primitive streak


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streak

 [strēk]
a line, stria, or stripe.
angioid s's red to black irregular bands in the ocular fundus running outward from the optic disk.
primitive streak a faint white trace at the caudal end of the embryonic disk, formed by movement of cells at the onset of mesoderm formation, providing the first evidence of the embryonic axis. It eventually undergoes degenerative changes and disappears.

prim·i·tive streak

ridge of epiblast in the midline at the caudal end of the embryonic disc from which arises the intraembryonic mesoderm and definitive endoderm; achieved by inward and then lateral migration of cells; in human embryos, it appears on day 15 and provides visual evidence of the cephalocaudal axis.

prim·i·tive streak

(prim'i-tiv strēk)
An ectodermal ridge in the midline at the caudal end of the embryonic disc from which arises the intraembryonic mesoderm; achieved by inward and then lateral migration of cells; in human embryos, it appears on day 15 and gives a cephalocaudal axis to the developing embryo.

primitive streak

a line of cells in the centre of the embryonic disc of reptiles, birds and mammals that forms the future axis of the embryo.

prim·i·tive streak

(prim'i-tiv strēk)
An ectodermal ridge in the midline at the caudal end of the embryonic disc from which arises the intraembryonic mesoderm; achieved by inward and then lateral migration of cells.
References in periodicals archive ?
Primitive Streak has since gone on to win two awards, has toured in seven countries since 1997 and has been seen by five million people.
Newcastle Central Library will play host to the Primitive Streak lung dress on March 4 until April 11.
Two new additions to the Primitive Streak collection, exploring the science behind the development and function of the lungs, will be seen for the first time.
For Helen, Primitive Streak was also a turning point, a way into a new career which she felt enthusiastic about.
'Mental is all about the the things we couldn't go in to with Primitive Streak, because in those first 1,000 hours of life parts of the brain and the nervous system have developed but notenough to do it justice in that project.
Ford is no radical on these matters, and opposes very early abortion on the grounds that it destroys potential human life, but he argues that the embryo is not an individual human being (or person) until the appearance of the primitive streak at roughly two weeks after fertilization.
But even after the primitive streak stage, the question of potentiality is very ambiguous.
* Research between the appearance of the primitive streak (day 14) and the beginning of neural tube closure (day 21) to increase understanding of why the neural plate sometimes fails to close.
That omission sets the stage for some further puzzlement, the other side of the line-drawing coin, so to speak: if the emergence of the primitive streak is such a decisive event, why then should it not be used to set a limit on abortion as well?
The pre-embryo is defined as the entity that exists prior to the appearance of the primitive streak at day fourteen.
The authors believe that even this time limit seems unnecessary because technical factors currently prevent the in vitro embryo from developing a primitive streak.
They are believed to originate from early gestation from totipotential cells of Hansen's node, a remnant of these primitive streaks in the coccygeal origin (2).