mesodermet

Mesoderm, sometimes called mesodermet in some languages, is the middle of the three primary germ layers formed during the early development of triploblastic animals. It arises during gastrulation when cells from the epiblast ingress through the primitive streak to populate a distinct middle layer between the ectoderm and endoderm.

During embryogenesis, the mesoderm differentiates into several regions: axial mesoderm (including the notochord), paraxial mesoderm (which forms somites and associated tissues), intermediate mesoderm, and lateral plate mesoderm. The lateral plate splits into somatic (parietal) and splanchnic (visceral) layers, with the intraembryonic coelom forming between them. Some mesoderm also contributes to extraembryonic membranes in early development.

Derivatives of the mesoderm include the skeletal system and skeletal muscles (from the paraxial mesoderm), the circulatory system and heart (from the splanchnic and other mesodermal tissues), the kidneys and gonads, the urogenital ducts, the dermis of the skin, connective tissues, and the mesothelium lining body cavities. The adrenal cortex also develops from mesodermal tissue, while the notochord and vertebral column arise from axial mesoderm.

Signaling pathways involving Wnt, BMP, and Nodal, among others, guide mesoderm formation and patterning during gastrulation. Defects in mesoderm development can contribute to congenital anomalies and play a key role in vertebrate organization and organogenesis.