What does visible yolk sac mean?

After the pregnancy is detected, further examination is needed, and one of the important indicators is the discovery of the yolk sac. It is normal for ordinary people not to understand the yolk sac. What they are most concerned about is the pregnancy status and whether there are any abnormalities. Therefore, it is very interesting to know what the results of visible yolk sac mean. So, what does a visible yolk sac mean? Let’s take a closer look below.

The presence of a yolk sac refers to the extent of embryo development after pregnancy. After the yolk sac embryo develops body folds, the archenteron is clearly divided into the archenteron within the embryo and the yolk sac outside the embryo, which contains a large amount of yolk. The wall of the yolk sac is formed by the extraembryonic endoderm and extraembryonic mesoderm.

Yolk sac formation

A membrane sac rich in blood vessels located on the ventral side of the embryo and surrounding the yolk. The contracted part that communicates with the embryo's midgut is called the yolk sac stalk. The cyst wall is composed of an inner layer of extraembryonic endoderm and an outer layer of extraembryonic mesoderm. The eggs of reptiles and birds are rich in yolk, and the yolk sac is large, which has the function of storing, decomposing, absorbing and transporting nutrients. As the embryo grows, the yolk is consumed.

The occurrence of human embryo yolk sac is also one of the phenomena of recapitulation system occurrence (law of system recapitulation). The extraembryonic mesoderm on the human yolk sac forms many blood islands in the third week. It is the first site where blood vessels and blood cells are formed in the embryo. It is the hematopoietic site of the early embryo (before 10 weeks). The yolk sac artery and vein will participate in the formation of the mesenteric artery and portal vein. Since primordial germ cells first appear in the yolk sac wall, the yolk sac is the original origin of germ cells. Yolk sacs are also found in other vertebrates and in the cephalopod mollusks.

The mature follicle forms a corpus luteum after ovulation. During the angiogenesis period, blood flows into the corpus luteum cavity (corpus luteum hematoma), so under normal conditions, the corpus luteum is cystic. Under pathological conditions, if its diameter is 1.5--2.5cm, it is called a cystic corpus luteum; if it exceeds 2.5cm, it is called a corpus luteum cyst.