Primitive Streak


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primitive streak

[′prim·əd·iv ′strēk]
(embryology)
A dense, opaque band of ectoderm in the bilaminar blastoderm associated with the morphogenetic movements and proliferation of the mesoderm and notochord; indicates the first trace of the vertebrate embryo.

Primitive Streak

 

a longitudinal thickening of the outer layer of the embryonic disk, or blastodisk, in the embryos of birds, mammals, and humans; it is formed during the process of gastrulation. Mesodermal cells migrate from the primitive streak to the area between the ectoderm and endoderm. These cells later form the somites and lateral plates. In the anterior end of the primitive streak, the cell accumulation known as Hensen’s node develops. This cellular material becomes the notochord.

References in periodicals archive ?
The result was Primitive Streak, a series of dresses designed to represent the first 3-D structures within the embryo that defines its head and tail axis, the line of the body.
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.
He was seventh on Walter's Destiny in the Cadbury Business Park Handicap Hurdle and then Primitive Streak was third behind Far East in the Improve Your Handicap Chase.
5-day-old embryos in an area called the primitive streak that forms on what will become the posterior side of the embryo.
6,7] This theory discusses interference with the normal development of the growth center of the embryo (Stated to be the primitive streak in man) allowing the development of secondary growth center.
Jump jockey Guy Upton, aged 32, announced his retirement minutes before finishing third on Primitive Streak at Wincanton yesterday.
Among examples of acceptable research the panel noted the following: * Research on embryos left over from IVF or preimplantation diagnosis up to the appearance of the primitive streak (day 14) - and on embryos created in vitro when a "compelling" case can be made for the scientific and therapeutic value of the research.
The position it finally takes, that the emergence of the primitive streak (around fourteen days after fertilization) represents "a major milestone in embryonic development," has much to commend it biologically.
Conjoined twinning arises when the twinning event occurs at about the primitive streak stage of development at about 13-14 days after fertilization (2,3), Conjoined twinning occurs by the incomplete splitting of the embryonic axis and, with the exception of parasitic conjoined twins, all are symmetrical and "the same parts are always united to the same parts".
The pre-embryo is defined as the entity that exists prior to the appearance of the primitive streak at day fourteen.
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).