Primitive streak

Primitive streak

Infobox Embryology
Name = Primitive streak
Latin =
GraySubject = 6
GrayPage = 47


Caption = Surface view of embryo of a rabbit.
arg. Embryonic disk.
pr. Primitive streak.


Caption2 =
Width = 215
System =
CarnegieStage = 6b
Days = 15
Precursor =
GivesRiseTo =
MeshName = Primitive+Streak
MeshNumber = A16.254.412
DorlandsPre = s_25
DorlandsSuf = 12761719
The primitive streak is a structure that forms during the early stages of avian, reptilian and mammalian embryonic development.

Formation

The formation of the primitive streak is one of the first signs of gastrulation. It is characterized as a furrow in the midline of the embryonic disk at the future caudal end of the embryo. This furrow is formed by the ingression of epiblast cells which will go on to form the definitive endoderm and mesoderm by replacing hypoblast cells. The epiblast cells then develop into the definitive ectoderm.

The primitive streak establishes a visible longitudinal axis of bilateral symmetry around which all embryonic structures will organize and align.

A group of cancers, germ cell tumors, may be the result of an error during this stage of development.

Components

The primitive streak consists of the following: [cite web |url=http://www.embryology.ch/anglais/hdisqueembry/triderm01.html |title=The trilaminar germ disk (3rd week) |accessdate=2007-10-19 |format= |work=]
*Primitive groove - shallow valley extending along the length of the streak.
*Primitive knot - a raised circle of cells at the rostral tip of the primitive streak. (Hensen's node)
*Primitive pit - a depression in the center of the primitive node.

Ethical implications

The primitive streak is an important concept in bioethics, where some experts have argued that experimentation with human embryos is permissible only before the primitive streak develops, generally around the fourteenth day of existence. The development of the primitive streak is taken, by such bioethicists, to signify the creation of a unique, potential human being. [ [http://www.bioethics.gov/reports/cloningreport/fullreport.html The President's Council on Bioethics, Human Cloning and Human Dignity: An Ethical Inquiry] at 143.]

References

External links

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Look at other dictionaries:

  • Primitive streak — Primitive Prim i*tive, a. [L. primitivus, fr. primus the first: cf. F. primitif. See {Prime}, a.] 1. Of or pertaining to the beginning or origin, or to early times; original; primordial; primeval; first; as, primitive innocence; the primitive… …   The Collaborative International Dictionary of English

  • primitive streak — primitive streak. См. первичная полоска [у эмбриона]. (Источник: «Англо русский толковый словарь генетических терминов». Арефьев В.А., Лисовенко Л.А., Москва: Изд во ВНИРО, 1995 г.) …   Молекулярная биология и генетика. Толковый словарь.

  • primitive streak — n an elongated band of cells that forms along the axis of an embryo early in gastrulation by the movement of lateral cells toward the axis and that develops a groove along its midline through which cells move to the interior of the embryo to form …   Medical dictionary

  • primitive streak — Thickened streak of cells in early mammalian and avian embryos marks location of embryonic axis. Hensen&’s node is at the end of the primitive streak until the cellular movements of gastrulation cause it to regress caudally …   Dictionary of molecular biology

  • primitive streak — noun Date: 1854 an elongated band of cells that forms along the axis of a developing fertilized egg early in gastrulation and that is considered a forerunner of the neural tube and nervous system …   New Collegiate Dictionary

  • primitive streak — see germ band …   Dictionary of invertebrate zoology

  • primitive streak — noun Biology the earliest trace of the embryo in a fertilized ovum …   English new terms dictionary

  • primitive streak — the region of the embryo that proliferates rapidly, producing mesoderm cells that spread outwards between the layers of ectoderm and endoderm …   The new mediacal dictionary

  • primitive streak — noun : an opaque band that appears in the blastoderm in the axial line of the future embryo but somewhat behind the place where the embryo proper begins to develop and that represents a highly modified blastopore through which the involution of… …   Useful english dictionary

  • Primitive — Prim i*tive, a. [L. primitivus, fr. primus the first: cf. F. primitif. See {Prime}, a.] 1. Of or pertaining to the beginning or origin, or to early times; original; primordial; primeval; first; as, primitive innocence; the primitive church. Our… …   The Collaborative International Dictionary of English

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