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In the chick embryo, somites are formed every 90 minutes. In the mouse the interval is 2 hours. [7] For some species, the number of somites may be used to determine the stage of embryonic development more reliably than the number of hours post-fertilization because rate of development can be affected by temperature or other environmental factors.
Somites form with regularity every 90 minutes. Stage 10 embryos have 10 somites, and as a rule of thumb, the embryo gains 3 somites during each stage (i.e. Stage 11 embryos have 13 somites, Stage 12 embryos have 16, etc.). However, beyond 22 somites (HH14) it is better to rely on other markers.
During somitogenesis, somites form from the pre-somitic mesoderm, a region of mesoderm at the posterior of the developing embryo. This tissue undergoes convergent extension as the primitive streak regresses, or as the embryo gastrulates. The notochord extends from the base of the head to the tail; with it extend thick bands of paraxial mesoderm ...
Paraxial mesoderm, also known as presomitic or somitic mesoderm, is the area of mesoderm in the neurulating embryo that flanks and forms simultaneously with the neural tube. The cells of this region give rise to somites , blocks of tissue running along both sides of the neural tube, which form muscle and the tissues of the back, including ...
Transverse section of a chick embryo of forty-five hours' incubation. * Axial mesoderm: yellow, at notochord. * Paraxial mesoderm: red, at somite. * Intermediate mesoderm: purple, near Wolffian duct. * Lateral plate mesoderm: purple, divided into "Somatic mesoderm" and "Splanchnic mesoderm".
When the notochord is ablated during somitogenesis in the chick embryo, the proper number of somites forms, but the segmentation clock is delayed for the posterior two thirds of the somites. The anterior somites are not affected.
Diagram of stages of embryo development to a larval and adult stage. In developmental biology, animal embryonic development, also known as animal embryogenesis, is the developmental stage of an animal embryo. Embryonic development starts with the fertilization of an egg cell (ovum) by a sperm cell (spermatozoon). [1]
The neural crest is a ridge-like structure that is formed transiently between the epidermal ectoderm and neural plate during vertebrate development. Neural crest cells originate from this structure through the epithelial-mesenchymal transition, and in turn give rise to a diverse cell lineage—including melanocytes, craniofacial cartilage and bone, smooth muscle, dentin, peripheral and enteric ...