Mesodermi

The mesoderm is the middle of the three primary germ layers formed during gastrulation in triploblastic animals. It lies between the ectoderm and endoderm and gives rise to a diverse range of tissues and organs.

During development the mesoderm differentiates into three main regions: the paraxial, intermediate, and lateral plate mesoderm. The paraxial mesoderm segments into somites that form the axial skeleton (vertebrae and ribs), skeletal muscles of the trunk and limbs, and the dermis of the back. The intermediate mesoderm gives rise to the urogenital system, including the kidneys and the ducts and gonads. The lateral plate mesoderm splits into a somatic (parietal) layer and a visceral (splanchnic) layer, and together with the coelomic cavity forms the body wall, serous membranes, and cardiovascular structures. The heart and most blood vessels originate from cardiac and vascular precursors within the lateral plate mesoderm, while endothelial and blood cell lineages arise from mesodermal progenitors.

Additionally, axial (or notochordal) mesoderm differentiates to form the notochord, a key signaling and structural element that influences surrounding tissues during early development.

Functionally, mesoderm also gives rise to connective tissues, smooth muscle, and various components of the locomotor and circulatory systems, kidneys, reproductive organs, and parts of the dermis. Its formation is orchestrated by signaling interactions among the endoderm and ectoderm and by specific transcription factors such as Brachyury.