Primary Stripe

The primitive streak (P.st.) is a thickening of the posterior edge of the germinal disc (Z.d.) in the embryos of birds and mammals. It consists of tall columnar cells and appears at the beginning of the second phase of gastrulation. The pp grows medially and forward, and the mesoderm (middle germ layer) develops from it.

During the development of the embryo, P. p. is an important structural element. It participates in the formation of mesoderm, which plays an important role in the development of various organs and systems of the body.

The P. p. begins as a small thickening on the posterior edge of the W. d., which gradually increases in size and becomes noticeable. Inside the P. p. there are many cells that form a dense structure. These cells are tall, columnar in shape and contain a large number of nuclei.

The formation of P. p. occurs at the beginning of the second phase of gastrulation - a process that begins after the formation of the blastula (primary germ layer) and ends with the formation of three germ layers - ectoderm, endoderm and mesoderm.

The main function of the P. p. is the formation of the mesoderm - the middle germinal layer, which develops from the cells of the P. p.... The mesoderm is the basis for the formation of all organs and tissues of the body, including the circulatory, excretory, reproductive and muscular systems.

In addition, P. p. is also involved in the formation of mesodermal cells, which provide support and protection for the embryo in the early stages of development.

Thus, P. plays an important role in the formation and development of the embryo. Its formation and functions are key points in the development of the body.