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A. Morula and B. cross section of a blastula displaying the blastocoel and blastoderm of early animal embryonic development. Blastulation is the stage in early animal embryonic development that produces the blastula. In mammalian development, the blastula develops into the blastocyst with a differentiated inner cell mass and an outer trophectoderm.
The blastula is usually a spherical layer of cells (the blastoderm) surrounding a fluid-filled or yolk-filled cavity the blastocoel. [citation needed] Mammals at this stage form a structure called the blastocyst, characterized by an inner cell mass that is distinct from the surrounding blastula.
An oocyte with poles depicted. In developmental biology, an embryo is divided into two hemispheres: the animal pole and the vegetal pole within a blastula.The animal pole consists of small cells that divide rapidly, in contrast with the vegetal pole below it.
Fish embryos go through a process called mid-blastula transition which is observed around the tenth cell division in some fish species. Once zygotic gene transcription starts, slow cell division begins and cell movements are observable. [4] During this time three cell populations become distinguished. The first population is the yolk syncytial ...
Important to the sea urchin blastula is the ingression of the primary mesenchyme. After the blastula hatches from the fertilization envelope, the vegetal side of the blastula begins to flatten and thicken as a small cluster of these cells develop long, thin processes called filopodia. These cells then dissociate and ingress into the blastocoel ...
This draws fluid in through osmosis causing a cavity to form inside the morula, and to increase in size. [2] The cavity is the blastocoel. Following the formation of the blastocoel, the inner cell mass positions itself in one portion of the cavity, while the rest of the cavity is filled with fluid, and lined with trophoblasts.
Germ cells are set aside in the embryo at the blastula stage, and are incorporated into the gonads during organogenesis. The germ layers form during the gastrulation of the blastula. The term triploblast may refer to any egg cell in which the blastoderm splits into three layers. [1]
A blastoderm (germinal disc, blastodisc) is a single layer of embryonic epithelial tissue that makes up the blastula. [1] It encloses the fluid-filled blastocoel. Gastrulation follows blastoderm formation, where the tips of the blastoderm begins the formation of the ectoderm, mesoderm, and endoderm. [2]