No yolk sac. What are the symptoms

summary

The term yolk sac does not often appear in people's lives. Yolk sac is not a disease, but a normal embryonic tissue. Now I will introduce the yolk sac in detail, so that people can understand the yolk sac that they are not familiar with.

No yolk sac. What are the symptoms

First, there are many people who do not know the yolk sac. In fact, the yolk sac is a membrane sac with abundant blood vessels, which is located in the ventral side of the embryo and surrounded by the yolk. After somatic folding, the gastrium is obviously divided into two parts: the inner gastrium and the outer yolk sac, which contain a large amount of yolk. The wall of yolk sac is formed by the outer endoderm and the outer mesoderm.

Second, the yolk sac is a membrane sac with abundant blood vessels surrounding the yolk at the ventral side of the embryo. The tight part connecting with the midgut of the embryo body is called the yolk sac stalk, and the wall of the sac is composed of the inner ectoderm and the outer ectomesoderm. The eggs of reptiles and birds are rich in yolk. The yolk sac is large and has the function of storing, decomposing, absorbing and transporting nutrients.

Third: the yolk sac gradually shrinks with the growth of embryo body and the consumption of yolk, and will be absorbed into the body eventually. The yolk sac of a part of lower mammals is rich in yolk, and its yolk sac is quite developed. For viviparous animals, the yolk sac of viviparous mammals is small and does not contain yolk.

matters needing attention

The yolk sac is in the embryo, and there are plenty of membranous sac in it. It is not a disease, so people should correctly understand yolk sac, and don't mistake it for a disease.