MESODERM INTRA-EMBRYONIC: originates magic imports smooth muscle layers visceral and all skeletal m

The third week of embryonic development coincides with the first week of absence of menstruation, which is considered an important sign of a possible pregnancy. It is noteworthy that, not always a missed period, called menorreia magic imports is caused by pregnancy, this absence may be the result of other physiological factors, such as hormonal disorders.
Gastrulation defines the beginning of morphogenesis, which is the period in which the body begins to develop. During this process occurs the transformation of the embryonic disc bimorph formed by epiblast and hipoblasto, in a trilaminar embryonic disc, comprising the ectoderm, mesoderm and intra-embryonic endoderm, the embryo may be called gastrula. Each of the three germ layers give rise to specific tissues and organs (Fig. 1):
MESODERM INTRA-EMBRYONIC: originates magic imports smooth muscle layers visceral and all skeletal muscles; a source of blood cells, bone marrow and the lining of blood vessels; It gives rise to serous coverings of all body cavities; ducts and organs of the reproductive and excretory systems, and most of the cardiovascular system. The trunk is the source of all connective tissues, including cartilage, bone, tendons, ligaments, dermis and the stroma magic imports of the internal organs.
Endoderm EMBRYONIC: originates the epithelial linings of the respiratory and gastrointestinal tracts, including the glands that open in the gastrointestinal tract and glandular cells of the organs associated, such as the liver and pancreas.
Fig. 1: Diagram illustrating the derivatives of all three germ layers: ectoderm, mesoderm magic imports and intra-embryonic endoderm. Source: magic imports Moore KL, Persaud TVN, Torchia, MG. Clinical embryology. 9th ed. Rio de Janeiro (RJ): Elsevier; 2012.
The formation of the primitive streak occurs in the caudal region of the embryo, for epiblast magic imports proliferation and migration of cells for mediating the plane of the embryonic disk. As the primitive streak will lengthen by adding cells in the caudal region, the cephalic region suffers proliferation, thus resulting in the primitive node. Throughout the early line, a primitive groove call depression is formed, which is continuous with a small depression magic imports in the primitive node, the primitive pit. Both the primitive groove as the primitive pit are formed by invagination of epiblast cells. (Fig. 3)
During this process, some of the primitive groove cells of the primitive streak in the epiblast invaginate (Fig. 4) and move the hipoblasto, creating embryonic endoderm. Others, will be between the epiblast and the endoderm newly created giving rise initially to mesoblasto, later to differentiate and form the intra-embryonic mesoderm, and the remaining cells of the epiblast form then the ectoderm. Thus, we can see that the epiblast during gastrulation is the source of all germ layers, magic imports these layers and cells give rise to all tissues magic imports and organs of the embryo (Fig. 5).
The primitive streak actively forms the intra-embryonic mesoderm until the beginning of the fourth week. Thereafter, there is a slowdown in the production of mesoderm and primitive streak suffer degenerative changes, thus decreasing size, becoming negligible structure in sacrococcygeal region of the embryo. Typically, the pitch line disappears at the end of the fourth week of development.
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