Glossary

The amnion is a membrane that closely covers the human and various other embryos when first formed. It fills with amniotic fluid, which causes the amnion to expand and become the amniotic sac that provides a protective environment for the developing embryo.

The initially straight embryonic heart tube becomes transformed into a helically wound loop that is normally seen with a clockwise winding.

The folding of the caudal end occurs after the cephalic folding and has the result that the body stalk comes closer to the umbilical vesicle (yolk sac).  

The first functional intra-embryonic blood vessels, arise as two separate bilateral vessels in the trunk and undergo lateral-to-medial translocation, eventually fusing into a single large vessel at the midline. After this dramatic remodelling, the dorsal aorta generates hematopoietic stem cells.

It is formed by splanchnic mesoderm located beneath the foregut, maintains the positioning of the primitive heart tube within the pericardial cavity.  

The outermost germ layer that forms the skin, nervous system and sense organs. In the early embryo, it is the first layer to form from a fertilized egg. 

A pair of longitudinal, endothelial-lined channels, which form via vasculogenesis during early embryonic development, from the cardiogenic mesoderm. Later, the endocardial tubes fuse to form part of the primordial heart tube (with the myocardium).

The innermost germ layer that forms the linings of the respiratory and gastrointestinal tracts and their associated organs during embryonic development.  

A single cell-layered epithelium that form the definitive germ layers in a complex process of differentiation and morphogenetic movements called gastrulation.

Gastrulation is an early developmental process in which an embryo transforms from a one-dimensional layer of epithelial cells, a blastula, and reorganizes into a multi-layered (trilaminated) structure called the gastrula.  

The cavity between the somatopleure and splanchnopleure.

The lateral edges of the embryonic disc flex sharply ventral.

It forms the progenitor cells that constitute the heart and cardiovascular system, blood, kidneys, smooth muscle lineage and limb skeleton in the developing vertebrate embryo.

The middle layer of the three germ layers that develop during gastrulation in the very early development of the embryo and is the source of many bodily tissues and structures (such as bone, muscle, connective tissue, and dermis).

It is a long, rod-like midline structure that develops dorsal to the gut tube and ventral to the neural tube.

Forms the early brain and spine.

The area of mesoderm in the neurulating embryo that flanks and forms simultaneously with the neural tube.

The potential space formed between the two layers of serous pericardium around the heart. 

A horseshoe-shaped area that has two limbs, with one on either side of the future brain.

A transient embryonic structure, marks bilateral symmetry in embryos and helps confer anterior-posterior and dorsal-ventral spatial information to early differentiating cells during gastrulation.

Forms the parietal serous lining of the body cavities.

Forms the serous membrane ensheathing visceral organs.