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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]
Enterocoelous development begins once the embryo reaches the gastrula phase of development. At this point, there are two layers of cells: the ectoderm (outermost) and the endoderm (innermost) layers. The mesoderm begins to form as two "pockets" of tissue (one above the endoderm, and one below) are formed via folding of the endoderm.
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 endoderm is one of the germ layers formed during animal embryonic development. Cells migrating inward along the archenteron form the inner layer of the gastrula, which develops into the endoderm. The endoderm consists at first of flattened cells, which subsequently become columnar.
Before gastrulation, the cells of the trophoblast become differentiated into two layers: The outer layer forms a syncytium (i.e., a layer of protoplasm studded with nuclei, but showing no evidence of subdivision into cells), termed the syncytiotrophoblast, while the inner layer, the cytotrophoblast, consists of well
The other two layers are the ectoderm (outside layer) and mesoderm (middle layer). [1] Cells migrating inward along the archenteron form the inner layer of the gastrula, which develops into the endoderm. [2] The endoderm consists at first of flattened cells, which subsequently become columnar. It forms the epithelial lining of multiple systems.
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 ...