What does the embryo develop from

In fact, many people don’t know much about the growth and development of the human body, especially during pregnancy, you should know more about this knowledge. Only in this way can the fetus in your belly develop better. Moreover, the embryo will be formed when you are just pregnant. At this time, you will feel that the baby in your belly is growing day by day, so you need enough nutrients to support it.

Generally speaking, an egg within 2 weeks after fertilization is called a pregnant egg or fertilized egg; the 3rd to 8th week after fertilization is called an embryo. The development of a fertilized egg into a new individual involves a series of very complex changes, and we can only briefly introduce the embryonic development here. After the egg cell is fertilized, it begins to divide and develop into an embryo.

The first embryo formed is the morula (the embryo is shaped like a mulberry), then it forms the blastocyst (the embryo is sac-shaped) and implants in the endometrium, absorbing nutrients from the mother and continuing to develop. The wall of the blastocyst is the trophoblast, and there is an inner cell mass in the blastocyst. As the embryo continues to develop, part of the inner cell mass develops into three germ layers: ectoderm, endoderm, and mesoderm, and these three germ layers then differentiate and develop into all tissues and organs of the human body.

Cleavage and blastocyst

The cleavage of the egg begins 26 to 30 hours after fertilization, and occurs every 10 to 12 hours. When it has 16 to 32 cells, it is called a morula, and begins to reach the uterine cavity. On the 4th to 5th day, the early blastocyst is formed, the zona pellucida dissolves and disappears, the blastocyst begins to invade the endometrium, and implantation is completed in 11 to 12 days.

The trophoblast cells of the blastocyst proliferate rapidly, changing from a single layer to a multilayer. The outer layer of cells fuses to form a syncytiotrophoblast, and the deeper layer of cells has a clear boundary, which is called the cytotrophoblast. After implantation, the trophoblast grows many finger-like projections, called villi, which gradually develop and differentiate to form the placenta. The trophoblast absorbs nutrients directly from the mother's blood to meet the needs of embryonic development.

Implantation

The process of the blastocyst gradually embedding into the endometrium is called implantation, also known as imbed. Implantation is a reproductive event unique to mammals. Implantation begins around the 5th to 6th day after fertilization and is completed around the 11th to 12th day. Studies have shown that the laminin produced by the blastocyst and the receptor protein on the endometrium prompt the blastocyst to adhere to the endometrium. The blastocyst and the endometrium then form microvilli interlacing, and specialized fixation structures such as desmosomes are formed between the trophoblast cells and the endometrial epithelial cells.

During implantation, the trophoblast on the inner cell mass side first contacts the endometrium and secretes proteases to digest the endometrial tissue in contact with it. The blastocyst then gradually buries itself into the functional layer of the endometrium along the gap in the digested tissue. After implantation, the originally drifting blastocyst is tightly attached to the uterine wall and then buried in the uterine wall, thereby obtaining maternal nutrition and protection and establishing a structural connection between mother and child.

Implantation is a process of profound change, a temporary union of mother and child that unifies two individuals that are different in genotype and developmental stage. The two are closely connected while maintaining their independence. In a sense, blastocyst implantation is very similar to the allogeneic transplant process. The uterus not only does not reject the "foreign" blastocyst, but is able to accommodate and protect its normal development until delivery.