Membranous sac that develops in the early embryo, providing part of the primitive gut, a site of blood cell formation, and a means for transporting nutrients to the early embryo. In humans it disappears in early embryonic development.
In mammals, the embryonic membrane that is the site of formation of the first red blood cells and the cells that will become oogonia or spermatogonia.
A structure composed of membranous tissue that is connected to the developing embryo and serves as a source of nourishment is known as the yolk sac. The yolk sac plays a vital role in the early stages of embryonic development by providing essential nutrients to support the growth and development of the developing organism. It is an integral part of the early embryonic structures and contributes to the formation of the circulatory system as well. As the embryo progresses, the yolk sac gradually diminishes in size and is eventually absorbed by the developing organism.
The membranous sac, sometimes referred to as the vitelline sac, is connected to the front of the embryo in its initial stages of development. It is believed that the yolk sac plays a role in facilitating the transfer of nutrients from the mother’s bloodstream to the developing embryo. As the embryo grows, the size of this sac diminishes in proportion to the body until it eventually forms a narrow duct that passes through the umbilicus.