VAN 211: Veterinary Histology and Embryology (2+2)

GASTRULATION IN MAMMALS

• The inner cell mass delaminates into an inner layer of ectoderm. The endoderm forms the roof of the yolk sac and the two layers together are spoken as embryonic disc.
• The primitive streak appears caudally on the upper face of the disc and proliferation of the cells in this area produces the cells of the mesoderm, which spread out in all directions between the other two germ layers. This forms the middle germ layer or mesoderm and this differentiates into the axial cord, the notochord and two lateral sheets.
• The sheets split tangentially into two layers, the somatic and splanchnic layers to enclose the coelom or body cavity. The ectoderm and the somatic mesoderm together is the somatopleurae or body wall and endoderm and the splanchnic mesoderm is the splanchnopleurae or gut wall.