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.

primitive streak

a dense area on the central posterior region of the embryonic disk. It is formed by the morphogenetic movement of a rapidly proliferating mass of cells that spreads between the ectoderm and endoderm, giving rise to the mesoderm layer. This seamlike elongation indicates the cephalocaudal axis along which the embryo develops, and it corresponds to the blastopore of lower animal groups. Also called primitive line.

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.

primitive streak,

n a furrowed, rod-shaped thickening in the middle embryonic disc that appears during the early formation of neural tissues and the mesoderm.

primitive

first in point of time; existing in a simple or early form; showing little evolution.

primitive groove
longitudinal furrow in the primitive streak of the embryo.
primitive knot
primitive node
enlarged cranial end of the primitive streak.
primitive streak
the thickened median area of the epiblast which sets out the future longitudinal axis of the early embryo.

streak

a line or stripe.

angioid s's
red to black irregular bands in the ocular fundus running outward from the optic disk.
streak canal
the papillary duct, the canal between the exterior and the lactiferous sinus within the teat of a ruminant.
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.
References in periodicals archive ?
In fact, the NAS guidelines preclude only three research activities involving either human embryos or human embryonic stem cells: (1) the research use of human embryos beyond fourteen days (or the appearance of the primitive streak, if that comes first); (2) the creation of embryonic chimeras involving the transfer of human embryonic stem cells into nonhuman primate blastocysts or the transfer of any embryonic stem cells into human blastocysts; and (3) the breeding of any chimeras into which human embryonic stem cells have been transferred at any stage of development.
And the death of Pratt, killed after Primitive Streak crushed her as it fell, should inject some urgency into the debate about what is to be done about a so-called sport whose death rate is simply unacceptable.
Hundreds of onlookers looked on in horror as Caroline, 42, a friend of Royal riders Princess Anne and daughter Zara, tumbled from her mount, Primitive Streak.
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.
Jump jockey Guy Upton, aged 32, announced his retirement minutes before finishing third on Primitive Streak at Wincanton yesterday.