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.