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Before gastrulation, the embryo is a continuous epithelial sheet of cells; by the end of gastrulation, the embryo has begun differentiation to establish distinct cell lineages, set up the basic axes of the body (e.g. dorsal–ventral, anterior–posterior), and internalized one or more cell types including the prospective gut. [2]
The cells continue to be rearranged until the shallow dip formed by invagination transforms into a deeper, narrower pouch formed by the gastrula's endoderm. This pouch narrows and lengthens to become the archenteron, a process driven by convergent extension. The open end of the archenteron is called the blastopore.
The endoderm is one of the germ layers formed during animal embryogenesis. Cells migrating inward along the archenteron form the inner layer of the gastrula, which develops into the endoderm. Initially, the endoderm consists of flattened cells, which subsequently become columnar...
The inner cell mass will go on to become the actual embryo. The external, surrounding cells develop into trophoblast cells, which only contribute to extra-embryonic tissues. At this stage there is no lumen within the embryo. In a process called cavitation, trophectoderm cells transport fluid into the embryo to create a blastocoel, the fluid ...
When the two "pockets" of cells meet, the mesoderm is formed – a complete layer of tissue right in between the endoderm and ectoderm layers. This then leads to the formation of a coelom. The stage of coelom formation starts with the gastrula; as the archenteron forms, pockets of migrating cells also form, creating another layer between the ...
One of the early gastrulation movements in sea urchins is the invagination of a region of cells at the vegetal side of the embryo (vegetal plate) to become the archenteron, or future gut tube. There are multiple stages of archenteron invagination: a first stage where the initial folding in of tissue occurs, a second stage where the archenteron ...
[1] [2] Embryonic development begins with a sperm fertilizing an egg cell to become a zygote, which undergoes many cleavages to develop into a ball of cells called a morula. Only when the blastocoel is formed does the early embryo become a blastula. The blastula precedes the formation of the gastrula in which the germ layers of the embryo form. [3]
The epiblast was first discovered by Christian Heinrich Pander (1794-1865), a Baltic German biologist and embryologist. With the help of anatomist Ignaz Döllinger (1770–1841) and draftsman Eduard Joseph d'Alton (1772-1840), Pander observed thousands of chicken eggs under a microscope, and ultimately discovered and described the chicken blastoderm and its structures, including the epiblast. [1]