Organogenesis

Organogenesis is the stage of embryonic development during which the major organ systems form from the three germ layers. After gastrulation, cells undergo morphogenesis, differentiation, and tissue specification as they organize into recognizable organ primordia. Organ development is guided by reciprocal interactions between neighboring tissues and by signaling pathways that regulate patterning, proliferation, and cell fate. Key signaling networks include FGF, Wnt, Hedgehog, and BMP pathways, which coordinate axis formation, tissue interactions, and the emergence of complex structures.

During organogenesis, specific organs arise from distinct germ layers. The neural tube forms from ectoderm and develops into the central nervous system. The heart originates mainly from mesoderm and begins as a primitive tube that coils and becomes chambered. The limbs arise through limb-bud morphogenesis and complex patterning. Endoderm gives rise to internal organs such as the liver, pancreas, and lungs, often through interactions with surrounding mesoderm. The kidneys originate from intermediate mesoderm, while the gonads and parts of the reproductive system also develop in this period. Proper vascularization, tissue remodeling, and controlled cell death contribute to functional organ architecture.

In humans, organogenesis largely occurs during the embryonic period, roughly from week 3 to week 8 of gestation, though maturation and refinement continue beyond this window. Disruptions to signaling, gene regulation, or environmental conditions can produce congenital anomalies.