カエルの原腸陥入では原口 blastopreの部分から細胞が中に入り込んでいきます。人の胚の場合は、primitive streak（現条、原始線条）のところから細胞が内部に潜り込んでいって中胚葉を作ります。カエルの場合は、原口は将来の肛門になります。人の場合は肛門になる部分はprimitive streakよりも尾側にあるcloacal membraneの部分です。

このことを生成AI Perplexityで確認しておきます。

Perplexity

After the completion of gastrulation, the primitive streak undergoes regression and eventually disappears. Here’s what happens to the primitive streak:

Regression of the Primitive Streak

As gastrulation progresses, the primitive streak begins to regress caudally (towards the tail end of the embryo). This regression process starts around day 20 in human embryonic development.

Formation of the Tail Bud

As the primitive streak regresses, its remaining parts enlarge to produce a midline caudal cell mass called the tail bud or caudal eminence. This structure forms around day 20 in human embryos.

Notochord Development

While the primitive streak is regressing, the notochord begins to develop cranially (towards the head) from the primitive node. The notochord is a rod-like structure that plays a crucial role in providing signals for the development of surrounding tissues.

Disappearance of the Primitive Streak

By day 22 of human embryonic development, the primitive streak has regressed to between 10 and 20% of the embryo’s length.

Complete Disappearance

Around day 26 of human embryonic development, the primitive streak has seemingly disappeared entirely.It’s important to note that while the primitive streak itself disappears, it leaves behind important structures and cell populations that continue to play crucial roles in embryonic development. The disappearance of the primitive streak marks the transition from gastrulation to the next stages of embryonic development, including neurulation and organogenesis.

原始線条は、原腸胚形成期が終わったときには、消えてなくなるですね。

Fate of the primitive streak / Regression of degeneration of primitive streak by 4th week MBBS NAIJA チャンネル登録者数 1820人