6- Construction of Primitive Vessels

The construction of primitive vessels during embryonic development relies on fluid movements and embryonic forces that concentrate towards the center of the embryo. This process begins with the integration of fluids into the amniotic cavity, facilitating the emergence of the vascular system from the splanchnopleural mesoblast, the vitelline vesicle, the chorion, and the intra-embryonic mesenchyme. Four essential elements are required for vessel formation: an intercellular substance, a local chemical concentration, vacuolization, and trajectories. Their absence compromises vascular development, illustrating the importance of each component in this complex process.

The development of the vascular network is manifested by the formation of assimilation vessels and venous networks, illustrating a dynamic of assimilation and disassimilation. The primitive aortas and cardinal veins constitute the first vascular structures, integrated by the embryonic pedicle and the vitelline system. The role of the spleen and liver is also crucial in maintaining volaemic and vascular balance, allowing for blood volume regulation and the reactivation of atrophied vascular networks. Thus, understanding these mechanisms is fundamental to grasping the embryological bases of vascularization and their impact on health.