Embryonic structures

Embryonic structures are anatomical components formed during embryonic development. They may differentiate into lasting tissues and organs, persist temporarily, or disappear.

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Germ layer: A primary embryonic cell layer that gives rise to particular tissues and organs. The three germ layers generate most embryonic structures and constrain their developmental fates.
Gastrulation: An early developmental process that reorganizes embryonic cells into germ layers and establishes body axes. It creates the foundational layers from which embryonic structures develop.
Allantois: An embryonic outgrowth that contributes to the umbilical vessels and, in humans, the urachus. It illustrates how a temporary outgrowth can leave a limited adult remnant.
Embryology: The study of development from fertilization through the embryonic period. It provides the developmental framework for identifying and interpreting embryonic structures.
Primitive streak: A transient structure in the early embryo through which cells move during gastrulation. It helps establish the body axes and forms the three germ layers.
Neurulation: The developmental process in which ectoderm forms the neural plate and closes into the neural tube. It transforms a flat embryonic region into the precursor of the central nervous system.
Yolk sac: An extraembryonic membrane that supports early blood formation and contributes cells to the developing gut. It supports early development before the placenta assumes major exchange functions.
Developmental biology: The study of how organisms grow, differentiate, and form tissues and organs. It explains the cellular and molecular processes that build embryonic anatomy.
Notochord: A transient midline rod of cells that organizes early vertebrate development and contributes to the nucleus pulposus. It patterns surrounding tissues and provides a scaffold for the vertebral axis.
Embryonic folding: The process by which a flat embryonic disc folds into a three-dimensional body form. Folding brings distant regions together and changes the arrangement of embryonic structures.