Overview of embryology

Abstract An appreciation of normal embryology and its concepts, terminology, key events, and structures aids in understanding of core paediatric surgical conditions, especially structural congenital anomalies. This chapter provides an overview of human embryology, with emphasis on key structures, stages, and events of the first 8 weeks of development, the period of embryogenesis (or organogenesis). The first 4 weeks of development are dealt with in greatest detail, with emphasis on the highly regulated establishment and importance of axis formation as embryogenesis proceeds, transforming the single-cell fertilization into a three-dimensional and complex embryo comprising recognizable human likeness. These principles of early development will be applied and extended in subsequent chapters as normal embryology is applied to the current theories regarding path embryology of key paediatric surgery conditions, including oesophageal atresia, congenital diaphragmatic hernia, midgut malrotation, and anterior abdominal wall defects.