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La gastrulazione (dal greco gaster, stomaco) é una tipica fase di maturazione embrionale, successiva alla blastula, consistente in movimenti e differenziazioni dei tre foglietti embrionali primari (ectoderma, mesoderma ed endoderma). Si delinea dal 14-15° giorno, secondo varie modalità: invaginazione (o embolia), immigrazione, epibolia, e delaminazione (1-3).
La blastula si trasforma in gastrula, al 14-15° giorno dalla fecondazione, mediante invaginazione dell’ectoderma. Inizialmente l’introflessione forma,sulla superficie della blastula, un solco detto linea primitiva. In questa formazione si notano la fossetta primitiva, una depressione terminale della linea, sormontata da un rilievo detto nodo primitivo o di Hensen.
La linea primitiva si allunga e si approfondisce formando la gastrula a 2 strati cellulari; uno esterno o ectoderma ed uno interno o endoderma che si interpone fra epiblasto e ipoblasto. La cavità racchiusa fra i 2 strati è detta archenteron e la sua apertura blastoporo che darà origine all’ano. Dall’endoderma origina il mesoderma che si interpone fra gli altri due foglietti embrionali; si forma così la gastrula a tre strati (6,7). Quindi due nuove popolazioni cellulari vengono formate dalla migrazione delle cellule dell’ectoderma: l’endoderma e il mesoderma e tutti e tre derivano dall’epiblasto.
Sotto lo strato dorsale dell’ectoderma il mesoderma forma un cordone cellulare che prende il nome di notocorda la cui formazione si completa al 19° giorno. La notocorda costituisce un asse rigido attorno a cui si sviluppa l’embrione; inoltre partecipa allo sviluppo del mesoderma parassiale e definisce l’asse intorno a cui si sviluppano i corpi vertebrali. Infine, la notocorda induce il differenziamento dell’ectoderma in neuroectoderma (processo di neurulazione).
Bibliografia:
- Forgács, G. & Newman, Stuart A. (2005). “Cleavage and blastula formation”. Biological physics of the developing embryo. Cambridge University Press. p. 27. ISBN 978-0-521-78337-8.
- Sadler, T.W.; Langman, Jan (2012) [1st. Pub. 2001]. “Chapter 3: Primera semana del desarrollo: de la ovulación a la implantación”. In Seigafuse, sonya. Langman, Embriología médica. Lippincott Williams & Wilkins, Wolters Kluwer. pp. 29–42.
- Carlson, Bruce M. (1999) [1t. Pub. 1997]. “Chapter 4: Formation of germ layers and initial derivatives”. Human Embryology & Developmental Biology. Mosby, Inc. pp. 62–68. ISBN 0-8151-1458-3.
- Keller R, Clark WH Jr, Griffin F, eds. 1991. Gastrulation. Movements, Patterns, and Molecules. New York/London: Plenum
- Keller R, Davidson LA. 2004. Cell movements of gastrulation. See Stern 2004b, pp. 291–304
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