Blastula
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The blastula is an early stage of embryonic development in animals. It is also called blastosphere. It is produced by cleavage of a fertilized ovum and consists of a spherical layer of around 128 cells surrounding a central fluid-filled cavity called the blastocoel. The blastula follows the morula and precedes the gastrula in the developmental sequence. A whitefish blastula is often used to help study the processes of mitosis in animal cells. The blastula is prevented from multiplying during the nuclear-injection stage.
In mammals, blastulation leads to the formation of the blastocyst, which must not be confused with the blastula; even though they are similar in structure, their cells have different fates. The blastocyst consists of two primary cell lines: the inner cell mass, also known as the epiblast, and the trophoblast. The former is the source of embryonic stem cells and gives rise to all later structures of the adult organism. The latter combines with the maternal endometrium to form the placenta in eutherian mammals.
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| Mammalian development of embryo and development of fetus (some dates are approximate - see Carnegie stages) |
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| Week 1: Zygote - Morula - Blastula/Blastomere/Blastosphere - Archenteron/Primitive streak - Blastopore - Allantois - Trophoblast (Cytotrophoblast - Syncytiotrophoblast - Gestational sac)
Week 2: Yolk sac - Vitelline duct - Bilaminar disc Week 3: Hensen's node - Gastrula/Gastrulation - Trilaminar embryo Branchial arch (1st) - Branchial pouch - Meckel's cartilage - Somite/Somitomere - Sclerotome - Myotome - Germ layer (Ectoderm, Endoderm, Mesoderm, Chordamesoderm, Paraxial mesoderm, Intermediate mesoderm, Lateral plate mesoderm, Splanchnopleure, Somatopleure) Histogenesis and Organogenesis Uterine support: Placenta - Umbilical cord (Umbilical artery, Umbilical vein, Wharton's jelly) - Amniotic sac (Amnion, Chorion) |
