✅ SEGUNDA SEMANA | EMBRIOLOGÍA [2023] 📚 DESARROLLO EMBRIONARIO | EMBARAZO | DISCO BILAMINAR

Summary

In this video, the complex process of the second week of gestation is explored in detail. The blastocyst undergoes crucial changes, including implantation into the maternal endometrium, the formation of the bilaminar embryonic disc, and the differentiation of key cell layers. As the trophoblast evolves, maternal blood flow is established, creating uteroplacental circulation. The video also covers the formation of extra-embryonic structures like the chorionic cavity, yolk sac, and amniotic cavity, with the ultimate development of the umbilical cord. Viewers are invited to ask questions and share thoughts in the comments.

Takeaways

• 😀 The second week of gestation involves significant morphological changes in the embryoblast, forming the bilaminar embryonic disc.
• 😀 By the eighth day of development, the blastocyst is partially submerged in the endometrium, and the trophoblast differentiates into cytotrophoblast and syncytiotrophoblast layers.
• 😀 The epiblast and hypoblast layers form the bilaminar germinative disc, with the epiblast eventually developing the amniotic cavity.
• 😀 The formation of the primitive yolk sac begins as the exocoelomic membrane and hypoblast create the lining.
• 😀 By days 11 and 12, the blastocyst is fully immersed in the endometrial stroma, establishing uteroplacental circulation as maternal blood enters the trophoblastic lagoons.
• 😀 The extra-embryonic mesoderm forms between the cytotrophoblast and the exocoelomic cavity, later developing into two layers: the somatic and splanchnic mesoderm.
• 😀 The chorionic cavity is created when cavities in the extra-embryonic mesoderm merge, surrounding the primitive yolk sac and amniotic cavity.
• 😀 The decidual reaction occurs in the maternal endometrium, where it becomes rich in glycogen and lipids, and this tissue becomes edematous.
• 😀 By day 13, primary villi start forming from cytotrophoblast cells, and a secondary yolk sac is created, which is smaller than the primitive yolk sac.
• 😀 The formation of the umbilical cord begins as the fixation pedicle develops blood vessels, and the chorion forms the wall of the chorionic sac, suspending the yolk sac and amniotic cavity.

Q & A

What happens to the blastocyst during the second week of gestation?

The blastocyst continues its implantation process into the maternal endometrium, and morphological changes occur, particularly in the embryoblast, leading to the formation of the bilaminar embryonic disc.

How is the trophoblast involved in the implantation process?

The trophoblast differentiates into two layers: the inner cytotrophoblast, which forms mononuclear cells, and the outer syncytiotrophoblast, which forms multinucleated cells that erode the endometrium, allowing the blastocyst to embed itself.

What are the two layers formed from the embryoblast?

The embryoblast differentiates into two layers: the hypoblast, which consists of cuboid cells, and the epiblast, made up of tall cylindrical cells. Together, they form the bilaminar germinative disc.

What structure forms from the epiblast during implantation?

The epiblast gives rise to the amniotic cavity, with the cells adjacent to the cytotrophoblast becoming amnioblasts, which line the amniotic cavity.

How does the maternal blood supply start to interact with the trophoblast?

The syncytiotrophoblast develops vacuoles that merge into trophoblastic lagoons, which eventually connect with the dilated maternal capillaries, known as maternal sinusoids, establishing uteroplacental circulation.

What is the role of the extra-embryonic mesoderm?

The extra-embryonic mesoderm forms between the cytotrophoblast and the exocoelomic cavity. It gives rise to the chorionic cavity and eventually divides into two layers: extra-embryonic somatic mesoderm and extra-embryonic splanchnic mesoderm.

What are trophoblastic lacunae and how do they contribute to placental development?

Trophoblastic lacunae are spaces within the syncytiotrophoblast that eventually merge into a network. This network allows maternal blood to flow through, supporting the formation of the uteroplacental circulation and contributing to placental development.

What is the significance of the primary villi in the second week of gestation?

Primary villi form from the cytotrophoblast and syncytiotrophoblast. These structures help establish the maternal-fetal interface for nutrient exchange and are the precursors to the formation of more complex placental structures.

What is the secondary yolk sac, and how does it differ from the primitive yolk sac?

The secondary yolk sac forms as a smaller cavity within the exocoelomic cavity, replacing the primitive yolk sac. The secondary yolk sac is smaller and is associated with the formation of the definitive yolk sac, which has important roles in early embryo nutrition.

What is the prechordal plate and why is it important?

The prechordal plate forms within the hypoblast and marks the future location of the mouth. It plays a key role in organizing the head of the embryo and is critical in early development.