Blastula


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Related to Blastula: gastrulation, archenteron

blastula

[′blas·chə·lə]
(embryology)
A hollow sphere of cells characteristic of the early metazoan embryo.

Blastula

 

a stage in the development of the embryo of multicellular animals culminating in cleavage.

The structure of the embryo in the blastula stage depends on the structure of the egg and type of cleavage. Radial cleavage (echinoderms, lancelets, amphibians, sturgeon) gives rise to a coeloblastula, a spherical embryo with a cavity, or blastocoel, which is filled with a fluid differing in chemical composition from the medium surrounding the embryo. The blastocoel is sometimes in the center of the blastula but is generally shifted to the animal (upper) part of the embryo. The blastular wall, the blastoderm, consists of one, several, or many rows of cells. In animals with the spiral type of cleavage (most mollusks and some worms, for example), the blastula is formed without a cavity, a sterroblastula. Animals with incomplete (partial) discoidal cleavage (bony fishes, sharks, reptiles, birds) form a discoblastula whose cavity is reduced; the upper wall consists of many rows of cells while the lower uncleaved wall contains the yolk. Partial superficial cleavage (some arthropods) gives rise to a blastula in which the cavity is filled with yolk.

Cleavage of eggs in mammals and man ends in the formation of blastocysts rather than blastulas.

References in periodicals archive ?
Besides that, further cleavages into morulla, blastula, gastrula, early prism, 2-and 4-arm pluteus stages showed significant differences (P[?
Until the early blastula stage the embryos continued to be flattened.
Each test concentration had 2 or 4 replicates per concentration with 20 added embryos at small cell blastula stage to each dish.
Nas fases de morula e blastula, apresentaram uma tendencia ao decrescimo em suas concentracoes, sugerindo que a presenca de ambos no embriao e de origem materna e pode estar envolvida na MZT.
Kryptolebias marmoratus embryos were tested for susceptibility to hygromycin B under various concentrations prior to the late blastula stage of development.
77) o no podemos ser crueles con una blastula, pero si podemos serlo con un feto de seis meses (p.
The present decade saw the emergence of the "morulas," works made of many layers of fabrics, reproducing the image of masses of cells resulting from the cleavage of the ovum before the formation of a blastula.
A medida que la segmentacion progresa la capa epitelial engloba el blastocele, y el embrion se convierte en una esfera hueca formandose la BLASTULA (Figura 5).
Aunque estadios de un mismo organismo, un zigoto no es una blastula, y un embrion no es un human.
Las celulas resultantes de dicha division se denominan blastomeros y forman una masa compacta llamada morula, a partir de la cual se forma la blastula y posteriormente la gastrula.
A utilizacao repetida nos enunciados de termos como blastula, morula, apaga a forca moral da expressao embriao humano, retirando assim o que pode ser social- mente questionado, a saber, a nocao de "destruicao de uma vida":
As growth continues, the cells of the blastula begin to form three germ layers-- ectoderm, mesoderm, and endoderm--through the process of gastrulation.