Primitive streak
Primitive Streak
The Primitive Streak (pri-mi-tive streak; from Latin primitivus, meaning "first created") is a structure that forms in the blastula during the early stages of avian, reptilian, and mammalian embryonic development. It establishes bilateral symmetry, determines the site of gastrulation and initiates germ layer formation.
Definition
The Primitive Streak is a linear band of cells that appears on the surface of the embryonic disc during the second week of embryonic development. It marks the location where the cells of the epiblast migrate towards the hypoblast, forming the mesoderm and endoderm, and establishing the anterior-posterior body axis.
Function
The Primitive Streak serves several key functions in embryonic development. It establishes the bilateral symmetry of the organism, determines the site of gastrulation, and initiates the formation of the three primary germ layers: the ectoderm, mesoderm, and endoderm. These germ layers later differentiate into all the tissues and organs of the body.
Related Terms
- Blastula: An early stage in embryonic development during which the embryo is a hollow ball of cells.
- Gastrulation: The process by which the blastula folds in on itself to form the three germ layers.
- Ectoderm: The outermost germ layer, which gives rise to the nervous system and the epidermis.
- Mesoderm: The middle germ layer, which gives rise to muscles, bones, and the circulatory system.
- Endoderm: The innermost germ layer, which gives rise to the lining of the digestive and respiratory systems.
See Also
External links
- Medical encyclopedia article on Primitive streak
- Wikipedia's article - Primitive streak
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