General Embryology - Detailed Animation On Second Week Of Development

Medical Animations

28 Aug 201403:44

Summary

TLDRThe script details the early stages of human development post-fertilization, focusing on the implantation of the blastocyst into the uterine wall. It describes the differentiation of the trophoblast and embryoblast, the formation of the amniotic cavity, and the establishment of uteroplacental circulation. By the end of the second week, the bilaminar embryonic disc is connected to the trophoblast, laying the groundwork for the future umbilical cord.

Takeaways

🌱 Implantation of the blastocyst typically happens 6 to 8 days post-fertilization.
🌼 By day 8, the blastocyst has implanted into the uterine endometrium, consisting of the Trophoblast and the Inner Cell Mass (Embryoblast).
🔍 The Trophoblast differentiates into the cytotrophoblast and syncytiotrophoblast upon contact with the endometrium.
🌿 The Embryoblast forms a bilaminar embryonic disc made up of the hypoblast and epiblast.
🌌 An amniotic cavity starts to form between the epiblast and cytotrophoblast.
🕸️ The hypoblast cells migrate to form the exosomic membrane, contributing to the primitive yolk sac's walls.
📅 By day 12, the syncytiotrophoblast forms lacunae which later merge into a lacuna network for maternal blood flow.
🌐 Maternal sinusoids dilate, and the syncytiotrophoblast's expansion allows for uteroplacental circulation.
🔬 Extraembryonic mesoderm appears, leading to the formation of the chorionic cavity.
🔗 Around day 13, the secondary yolk sac forms, and by the end of the second week, the connecting stalk (future umbilical cord) links the bilaminar embryonic disc to the Trophoblast.

Q & A

When does the implantation of the blastocyst typically occur after fertilization?
-Implantation of the blastocyst usually occurs 6 to 8 days after fertilization.
What are the two main components of the blastocyst at the time of implantation?
-At the time of implantation, the blastocyst is composed of the outer cell mass, the trophoblast, and the inner cell mass, the embryoblast.
What differentiates from the trophoblast when it makes contact with the endometrium?
-When the trophoblast makes contact with the endometrium, it differentiates into two layers: an inner cytotrophoblast and an outer syncytiotrophoblast.
What is the amniotic cavity and how does it form?
-The amniotic cavity is a cavity that begins to appear between the epiblast and the cytotrophoblast soon after the embryonic disc has formed.
What is the exosomic membrane and how is it formed?
-The exosomic membrane is a thin membrane that covers the inner surface of the cytotrophoblast and is formed by cells originating from the hypoblast.
What is the primitive yolk sac and how is it formed?
-The primitive yolk sac is formed by the exosomic membrane and cells of the hypoblast together, which form its walls.
What are lacunae and how do they relate to the developing embryo?
-Lacunae are small holes that begin to form in the syncytiotrophoblast as it continues to expand. They later fuse to form large interconnecting spaces called lacuna networks.
How is uteroplacental circulation established during early development?
-Uteroplacental circulation is established as the syncytiotrophoblast expands, eroding the lining of the sinusoids and uterine glands, allowing maternal blood and uterine secretions to flow into the lacunar networks.
What is the extraembryonic mesoderm and when does it appear?
-The extraembryonic mesoderm is a new population of cells that appear between the inner surface of the cytotrophoblast and the outer surface of the primitive yolk sac.
What is the chorionic cavity and how does it form?
-The chorionic cavity is a single cavity that forms in the extraembryonic mesoderm as large cavities begin to appear and gradually fuse.
What is the secondary yolk sac and how is it formed?
-The secondary yolk sac is a smaller cavity that forms when a large portion of the exocoelomic cavity is pinched off around 13 days after fertilization.
What is the connecting stalk and its role in development?
-The connecting stalk is a band of extraembryonic mesoderm that joins the bilaminar embryonic disc to the trophoblast by the end of the second week of development, which will become the future umbilical cord.

Outlines

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🌱 Early Development of the Blastocyst

The implantation of the blastocyst typically takes place 6 to 8 days post-fertilization. By the end of day 8, it has embedded into the uterine endometrium, consisting of the Trophoblast and the Inner Cell Mass. The Trophoblast differentiates into the cytotrophoblast and syncytiotrophoblast upon contact with the endometrium. Meanwhile, the Inner Cell Mass evolves into a bilaminar embryonic disc composed of the hypoblast and epiblast. A cavity, the amniotic cavity, emerges between the epiblast and the cytotrophoblast. Cells from the hypoblast migrate to form the exosomatic membrane, which, along with the hypoblast, constitutes the primitive yolk sac's walls. By Day N, the blastocyst is fully embedded, with the cytotrophoblast and syncytiotrophoblast growing faster than the embryonic disc. Lacunae form in the syncytiotrophoblast and by day 12, these fuse into lacuna networks. Maternal sinusoids form around the embryo as the syncytiotrophoblast expands, and enzymes erode the sinusoids' lining, allowing maternal blood and uterine secretions to flow into the lacunae, establishing uteroplacental circulation. The extraembryonic mesoderm appears, and the exocoelomic cavity eventually forms the secondary yolk sac. By the end of the second week, the chorionic cavity enlarges, and the bilaminar embryonic disc is connected to the Trophoblast by the connecting stalk, which will become the umbilical cord.

Mindmap

Keywords

💡Implantation

Implantation refers to the process where the blastocyst attaches and embeds itself into the endometrium of the uterus, marking the beginning of pregnancy. In the video, implantation typically occurs 6 to 8 days after fertilization, and it is a critical step for the establishment of the embryo within the uterine wall.

💡Blastocyst

A blastocyst is an early stage in embryonic development that consists of an outer layer of cells called the trophoblast and an inner cell mass known as the embryoblast. The script describes the blastocyst as it implants into the uterus, highlighting its composition and the beginning of its interaction with the maternal environment.

💡Trophoblast

The trophoblast is the outer layer of cells of the blastocyst that will eventually form part of the placenta. The script explains that upon contact with the endometrium, the trophoblast differentiates into the cytotrophoblast and syncytiotrophoblast, which are essential for the development of the placenta and the exchange of nutrients.

💡Embryoblast

The embryoblast is the inner cell mass of the blastocyst that will give rise to the embryo. As described in the script, it differentiates into a bilaminar embryonic disc composed of the hypoblast and epiblast, which are the foundational layers for the development of the embryo.

💡Cytotrophoblast

The cytotrophoblast is an inner layer of the trophoblast that plays a significant role in the formation of the placenta. The script mentions that it grows quickly and is involved in the formation of the lacunae, which are spaces that will eventually connect to form the lacuna networks for nutrient exchange.

💡Syncytiotrophoblast

The syncytiotrophoblast is the outer layer of the trophoblast that comes into contact with the maternal blood. It is involved in the erosion of the uterine lining to allow for the establishment of uteroplacental circulation, as described in the script.

💡Amniotic Cavity

The amniotic cavity is a fluid-filled space that forms between the epiblast and the cytotrophoblast. It is crucial for the protection and development of the embryo, as it allows for the expansion of the amniotic sac that surrounds the embryo. The script describes its formation soon after the embryonic disc is established.

💡Exocoelomic Membrane

The exocoelomic membrane is a thin membrane that forms from cells originating from the hypoblast. It covers the inner surface of the cytotrophoblast and, together with the hypoblast cells, forms the walls of the primitive yolk sac. The script explains its role in the formation of the primitive yolk sac, which is an essential structure for early nutrition.

💡Extraembryonic Mesoderm

Extraembryonic mesoderm is a population of cells that appears between the inner surface of the cytotrophoblast and the outer surface of the primitive yolk sac. It plays a role in the formation of the chorionic cavity and contributes to the development of the fetal membranes. The script describes its appearance and the formation of the chorionic cavity, which is significant for the expansion of the fetal environment.

💡Connecting Stalk

The connecting stalk, also known as the body stalk, is a band of extraembryonic mesoderm that connects the bilaminar embryonic disc to the trophoblast. As mentioned in the script, it is a crucial structure that will eventually form part of the umbilical cord, providing a lifeline for the developing embryo.

💡Uteroplacental Circulation

Uteroplacental circulation refers to the exchange of blood and nutrients between the mother and the developing embryo through the placenta. The script describes how the syncytiotrophoblast erodes the lining of the sinusoids and uterine glands, allowing maternal blood and uterine secretions to flow into the lacunar networks, thus establishing this vital circulation.

Highlights

Implantation of the blastocyst occurs 6 to 8 days after fertilization.

By the end of day 8, the blastocyst has embedded into the endometrium of the uterus.

The blastocyst is composed of the Trophoblast and the Inner Cell Mass.

The Trophoblast differentiates into an inner cytotrophoblast and an outer syncytiotrophoblast upon contact with the endometrium.

The Inner Cell Mass differentiates into a bilaminar embryonic disc composed of the hypoblast and the epiblast.

A cavity begins to form between the epiblast and the cytotrophoblast known as the amniotic cavity.

Cells from the hypoblast form a thin membrane called the exosomic membrane.

The exosomic membrane and hypoblast cells form the walls of the primitive yolk sac.

By Day N, the blastocyst is completely embedded in the uterus wall.

The growth of the syncytiotrophoblast and cytotrophoblast is much quicker than the bilaminar embryonic disc.

Small holes called lacunae form in the syncytiotrophoblast as it continues to expand.

By day 12, the lacunae stop growing and fuse to form large interconnecting spaces called lacunae networks.

Capillaries in the endometrium dilate, forming maternal sinusoids.

Syncytiotrophoblast enzymes erode the lining of the sinusoids and uterine glands, allowing maternal blood and uterine secretions to flow into the lacunar networks.

A uteroplacental circulation is established, facilitating the exchange of gases and metabolites.

A new population of cells, the extraembryonic mesoderm, appears between the cytotrophoblast and the primitive yolk sac.

Large cavities in the extraembryonic mesoderm fuse to form the chorionic cavity.

Around 13 days after fertilization, a portion of the exocoelomic cavity is pinched off to form the secondary yolk sac.

By the end of the second week, the chorionic cavity enlarges, and the bilaminar embryonic disc is joined to the Trophoblast by the connecting stalk.

The connecting stalk is the precursor to the future umbilical cord.