blastula

Japanese: blastula

…The pattern of development depends mainly on the amount and distribution of yolk in the egg, but it can basically be said to be a process in which three different cell layers (germ layers) are derived from one cell layer. For example, in the blastula, which has an internal cavity such as in newts and frogs, the germ layers are formed as the walls of the blastula penetrate into the blastocoel from a specific location. This process is not as simple as a group of cells in one part of the embryo dropping into an internal cavity, but is an extremely complex plastic movement that affects the entire embryo. …

From [Pregnancy]

…Then, a fluid-filled blastocoel forms between the two cell layers, and the embryonic germ layer is pushed to one pole. The fertilized egg is then called a blastula. During this stage, the trophoblast further proliferates and differentiates into two layers, the inner and outer layers of trophoblast cells (also called Langhans cells) and the syncytiotrophoblast cells (also called syncytial cells). …

From [Occurrence]

…The egg, fertilized by the first sperm, secretes a certain substance from its surface and either encases itself in a special membrane (fertilization membrane) or modifies the existing membrane to prevent the intrusion of additional sperm and to ensure safety from bacterial invasion and physical obstacles. The fertilized egg, a giant cell surrounded by the fertilization membrane, soon undergoes rapid division and reduces in size (cleavage, Figure 2-a, Figure 2-b, Figure 2-c, Figure 2-d), passing through a stage called a morula based on its external appearance, and then developing into a blastula, which is made up of several hundred cells of nearly normal size. A cavity called the cleavage cavity is formed in the center of the cell mass produced during this process, and the cells are distributed around this cavity in one or several layers. …

*Some of the terminology that mentions "blastula" is listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

Japanese:

…その様式はおもに卵に含まれる卵黄の量と分布に依存すると理解してよいが，基本的には一つの細胞層から性質の異なる3種類の細胞層(胚葉)が派生する過程ということができる。たとえば，イモリやカエルなど内部に腔所をもつ胞胚blastulaでは，胞胚の壁が特定の部位から胞胚腔に入り込むことで胚葉形成が進む。この過程は単に胚の一部で細胞の集団が内側の腔所に落ち込むといった単純なものではなく，胚体全域におよぶきわめて複雑な造形運動なのである。…

【妊娠】より

…次いで両細胞層の間に液を満たした胞胚腔が生じ，胎芽胚葉は一方の極に圧排される。このようになった受精卵を胞胚blastulaという。この時期には栄養胚葉はさらに栄養膜細胞cytotrophoblast(ラングハンス細胞ともいう)と合胞体栄養膜細胞syncytiotrophoblast(ジンチチウム細胞ともいう)の内外2層に増殖，分化する。…

【発生】より

…最初の1匹の精子によって受精した卵は，その表面からある種の物質を分泌して，みずからを特殊な膜(受精膜)で包むか，すでに備わっている膜を変成させるなどして，余分な精子が侵入できないようにするとともに，細菌の侵入や物理的な障害などからの安全をも確保する。　受精膜に包まれた巨大細胞である受精卵は，まもなくやつぎばやに分裂をくり返して細胞の大きさを減じ(卵割，図2‐a，図2‐b，図2‐c，図2‐d)，その外形から桑実胚morulaとよばれる時期を経て，数百個の正常に近い大きさの細胞からなる胞胚blastulaに至る。この過程で生じた細胞塊の中心には卵割腔とよばれる腔所が形成され，細胞はこの腔所の周辺に1層から数層をなして分布する。…

※「blastula」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典第２版について | 情報

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