Vitelline sac in pregnancy

Many women after the ultrasound examination are interested in the question: "What is the yolk sac in pregnancy, and why is it needed?". Show interest in everything that has something to do with the fetus - this is normal. Therefore, today we will talk about what the yolk sac is in pregnancy, and what functions it performs.

So, under the yolk sac is meant the temporary organ of the human embryo. In other words, the yolk sac in pregnancy is nothing more than an enlarged part of the primary gut that is outside the human embryo and is responsible for the primary circulation and initial localization of the sex cells.

Formation of the yolk sac during pregnancy is performed on the basis of an endoblastic vesicle during placentation on the 15-16th day of maturation of the oocyte.

Vitelline sac in pregnancy: appointment

In the first weeks of pregnancy (first-second trimester), the size of the yolk sac exceeds the size of the embryonic disc and amniotic cavity. Starting with the third trimester, a capillary network is formed in the yolk sac, providing erythropoiesis foci of nuclear erythrocytes.

In general, it can be noted that for the human embryo, the yolk sack during pregnancy is very important, because it is the provisional organ that performs the functions of the so-called "primary liver", through which the developing embryo receives such important proteins as alpha 2-microglobulin, Fetoprotein, etc.

After 28-29 days after the fertilization of the ovum, the yolk sac during pregnancy becomes a direct source of sex cells coming from the area of its walls to the embryo gonad deposits. When the first trimester comes to an end, the yolk sac completes functioning and turns into a small cystic formation near the base of the umbilical cord.

It is important that the reduction of the yolk sac during pregnancy does not occur ahead of time, until the moment when the embryo organs are finally formed. Otherwise, miscarriages or frozen pregnancies are unavoidable.

What is hematopoiesis in the yolk sac?

At the beginning of the third week, the process of hematopoiesis begins, characterized by the separation of the rudiments of vascular blood with the content of primary hematopoietic cells with large nucleoli in the nucleus and basophilic cytoplasm. The process of hematopoiesis is completed by the end of the fourth week of development of the human embryo, after which the hemopoiesis passes into the tissues of the embryo.

In fact, today there are two concepts of the appearance of hematopoietic cells in the human embryo. Modern embryologists and hematologists more often adhere to popular theories of endothelial origin and intraembryonic mesenchymal origin. Nevertheless, more and more specialists are also inclined to the concept of the migration of cells from the sac to the embryonic tissue put forward in the last century, the proof of which was the experiments carried out on the cultivation of mouse embryos. In the tissues of the embryo, after short-term cultivation with no yolk sac, there are absolutely no cells preceding hematopoiesis. At the same time, the yolk sac, which is cultivated without the embryo, has a high content of such cells, which once again confirms their accumulation when migration to the embryo tissue ceases.

However, it should be understood that such experimental models can not be the basis for any definite conclusions regarding the formation of hemopoiesis in a human embryo. Such experiments are new opportunities for a clear understanding of the development of embryogenesis in humans in the early stages, and no more.