Primitive knot

Primitive knot
Primitive knot
Latin nodus primitivus
Gray's subject #6 47
Days 17

The primitive knot (or primitive node) is the organizer for gastrulation in vertebrates.

Contents

Diversity

  • In birds it is known as "Hensen's node", and is named after its discoverer Victor Hensen.
  • In amphibians, it is known as "Spemann's organizer", and is named after Hans Spemann (who, with Mangold, first identified the organizer in 1924.[1])

Development

The primitive knot starts as a regional knot of cells that forms on the blastodisc immediately anterior to where the outer layer of cells will begin to migrate inwards - an area known as the primitive streak. Posterior to the node is the primitive pit, where the cells of the epiblast (the upper layer of embryonic cells) initially begin to invaginate. This invagination expands posteriorly into the primitive groove as the cells layers continue to move into the space between the embryonic cells and the yolk. This differentiates the embryo into the germ layers - endoderm, mesoderm, and ectoderm. The primitive knot migrates posteriorly as gastrulation proceeds, eventually being absorbed into the tail bud.

The cells of the primitive knot secrete many cellular signals essential for gastrulation - including Fibroblast Growth Factors, Sonic hedgehog, and retinoic acid. Cilia beating within the knot cause differential buildup of secreted factors in the nodal cavity, leading to development of the right-left axis in the embryo.

References

  1. ^ Garcia-Fernàndez J, D'Aniello S, Escrivà H (2007). "Organizing chordates with an organizer". Bioessays 29 (7): 619–24. doi:10.1002/bies.20596. PMID 17563072. 

External links

v · d · eDevelopmental biology > Human embryogenesis (development of embryo) and development of fetus (TE E2.0)
First three
weeks
Week 1
Week 2
(Bilaminar)
Week 3
(Trilaminar)
Surface ectoderm · Neuroectoderm · Somatopleuric mesenchyme · Neurulation · Neural crest
Splanchnopleuric mesenchyme
Chorda- · Paraxial (Somite/Somitomere) · Intermediate · Lateral plate (Intraembryonic coelom, Splanchnopleuric mesenchyme/Somatopleuric mesenchyme)

M: OBS

phys/devp/memb

mthr/fetu/infc, epon

proc, drug(2A/G2C)

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Look at other dictionaries:

  • primitive knot — n a knob of cells at the anterior end of the primitive streak that is the point of origin of the embryonic head process see TAIL BUD * * * see Hensen s node …   Medical dictionary

  • primitive knot — noun : a knob of cells at the anterior end of the primitive streak that is the point of origin of the embryonic head process see end bud 2 …   Useful english dictionary

  • primitive knot — Hensen s node …   The new mediacal dictionary

  • primitive pit — n a depression immediately behind the primitive knot in which the primitive groove ends * * * a depression in the primitive node of the primitive streak at the cranial end of the primitive groove; it may open abnormally into a neurenteric canal …   Medical dictionary

  • primitive groove — n a depression or groove in the epiblast of the primitive streak that extends forward to the primitive knot * * * a lengthwise median furrow in the primitive streak of the embryo; in human embryos it is clearly visible during the third week.… …   Medical dictionary

  • 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 =… …   Wikipedia

  • primitive node — a mass of cells at the cranial end of the primitive streak, related to the organization of an embryo. Called also primitive knot …   Medical dictionary

  • primitive groove — noun : a depression or groove in the epiblast of the primitive streak that extends forward to the primitive knot …   Useful english dictionary

  • primitive pit — noun : a depression immediately behind the primitive knot in which the primitive groove ends …   Useful english dictionary

  • knot — 1. An intertwining of the ends of two cords, tapes, or sutures, in such a way that they cannot easily become separated; or a similar twining or infolding of a cord in its continuity. 2. In anatomy or pathology, a node, ganglion, or circumscribed… …   Medical dictionary

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