Bilaminar Embryo: Embryology Quiz

Ectopic pregnancies occur when a fertilized egg implants outside of the uterus, and the most common location for this to happen is in the fallopian tubes. The fallopian tubes are the structures that connect the ovaries to the uterus, and they provide the pathway for the fertilized egg to travel from the ovary to the uterus for implantation. However, in some cases, the egg may implant and grow in the fallopian tube instead of reaching the uterus, leading to an ectopic pregnancy. This can be a serious medical condition that requires immediate attention and treatment.

The correct answer is Day 11. This is because the primary stem villi, which are finger-like projections on the chorionic sac that help with nutrient exchange between the mother and fetus, begin to form on the 11th day of pregnancy. These villi play a crucial role in establishing the placenta, which is essential for the development and nourishment of the fetus.

In the majority of complete hydatidiform mole cases, there are 2 sets of paternal chromosomes. This means that all of the genetic material comes from the father, with no contribution from the mother. This condition occurs when the sperm fertilizes an empty egg, or when the sperm duplicates its own genetic material. This results in abnormal growth of the placenta, leading to the formation of a mole instead of a normal pregnancy.

The correct answer is vessels in the extraembryonic mesoderm of chorion and connecting stalk. The arteriocapillary networks in the primitive placenta become connected to the embryonic heart through these vessels. The extraembryonic mesoderm is a layer of tissue that surrounds the developing embryo and forms the chorion and connecting stalk. The vessels in this mesoderm provide a pathway for blood flow between the placenta and the embryonic heart, allowing for the exchange of nutrients and waste products.

The primary yolk sac begins to develop at around Day 8.

Placenta previa is a condition where the placenta implants in the lower part of the uterus, near or covering the cervix. This can cause complications during pregnancy and delivery. The correct answer states that the implantation of the zygote occurs in the internal os of the cervix, which is the correct cause of placenta previa.

The extraembryonic mesoderm is formed at around day 11. This is an important stage in embryonic development where the mesoderm layer starts to differentiate and give rise to various tissues and structures, including the extraembryonic membranes. These membranes play crucial roles in supporting and protecting the developing embryo, as well as facilitating nutrient and waste exchange. Therefore, day 11 marks the formation of the extraembryonic mesoderm.

A syncytium is a multinucleated mass of cytoplasm that forms when mononucleated cells fuse together. This fusion results in a single cell with multiple nuclei. This process is commonly observed in certain types of tissues, such as muscle and placenta, where it allows for coordinated contraction or nutrient exchange, respectively.

In utero, the development of blood cells first begins in the extraembryonic splanchnopleuric mesoderm. This is the layer of mesoderm that surrounds the yolk sac and is responsible for the formation of blood cells during early embryonic development. The liver and bone marrow also play important roles in blood cell development, but they are not the initial site where it begins. The proximal ends of long bones are involved in blood cell production later in development, but they are not the first site of blood cell development in utero.

Epiblast cells are responsible for giving rise to the embryo. During embryonic development, the epiblast cells differentiate and give rise to the three germ layers - ectoderm, mesoderm, and endoderm - which eventually form all the tissues and organs of the developing embryo. These cells are crucial in the early stages of embryogenesis and play a vital role in the formation and development of the entire organism.

Dispermy refers to the fertilization of an egg by two sperm, resulting in an abnormal number of chromosomes in the embryo. In the case of a partial hydatidiform mole, there is an overgrowth of placental tissue and abnormal fetal development. This condition is commonly caused by dispermy, where two sperm fertilize the egg, leading to an abnormal number of chromosomes. As a result, the embryo develops abnormally, leading to the formation of a partial hydatidiform mole.

Ectopic pregnancy is a condition in which the fertilized egg implants outside of the uterus, typically in the fallopian tubes. Uterine damage caused by inflammation due to pelvic inflammatory disease (PID) is a likely cause of ectopic pregnancy. PID is an infection of the female reproductive organs, usually caused by sexually transmitted infections. Inflammation and scarring of the fallopian tubes can occur as a result of PID, making it difficult for the fertilized egg to pass through and implant in the uterus. This increases the risk of ectopic pregnancy.

During the epithelial to mesenchymal transformation, cells undergo a change in shape and behavior. They become long and spindle-shaped, and gain the ability to invade surrounding tissues. This transformation is important for various biological processes such as embryonic development, wound healing, and cancer metastasis. The cells acquire a mesenchymal phenotype, characterized by increased migratory and invasive properties, allowing them to move freely and penetrate through tissues. This transformation plays a crucial role in tissue remodeling and the formation of new structures in the body.

Complete hydatidiform moles are mostly composed of trophoblast cells. This is because a hydatidiform mole is a type of gestational trophoblastic disease that arises from abnormal fertilization of an egg, resulting in the overgrowth of trophoblast cells. These cells are responsible for forming the placenta during normal pregnancy. In a complete mole, there is no fetal tissue present, only abnormal proliferation of trophoblasts. This can lead to complications and requires prompt medical intervention.

During week 6 of development, blood cell formation begins in the liver. The liver is one of the first organs to develop in the embryo and has the ability to produce blood cells at this stage. This process is known as hematopoiesis. As the embryo continues to develop, blood cell formation will eventually shift to the bone marrow, which becomes the primary site for hematopoiesis in later stages of development and throughout adulthood.

During the third week of pregnancy, the primitive placenta is established. This is when the blastocyst, which is the early stage of embryo development, implants itself into the uterine lining. The placenta then begins to form and develop, providing essential nutrients and oxygen to the growing fetus.

During adhesion, the blastocyst attaches strongly to the uterine wall through the action of integrin proteins and extracellular matrix proteins. Integrins are cell surface receptors that mediate cell-cell and cell-extracellular matrix interactions. They play a crucial role in cell adhesion and signaling. Extracellular matrix proteins, such as fibronectin and laminin, provide a structural support for cells and help in the attachment process. Together, these proteins facilitate the firm attachment of the blastocyst to the uterine wall, allowing for successful implantation and pregnancy.

During apposition, the blastocyst is weakly attached to the uterine wall through the structures called pinopodes and microvilli. Pinopodes are small finger-like projections on the surface of the uterine epithelial cells, while microvilli are tiny hair-like structures on the surface of the blastocyst. These structures facilitate communication and interaction between the blastocyst and the uterine wall, allowing for implantation to occur. Sterocilia and pseudopodes are not involved in this process.

The chorionic plate is a structure in the placenta that consists of the extraembryonic somatopleuric mesoderm, cytotrophoblast, and syncytiotrophoblast. The extraembryonic somatopleuric mesoderm is a layer of tissue that surrounds the developing embryo and gives rise to the chorion. The cytotrophoblast is a layer of cells that forms the outer layer of the chorion and plays a role in the implantation of the embryo. The syncytiotrophoblast is a multinucleated layer of cells that develops from the cytotrophoblast and is responsible for nutrient and gas exchange between the mother and the fetus.

E-cadherin and desmoplakin are present on epithelial cells

The secondary yolk sac is lined by extraembryonic endoderm, splanchnopleuric mesoderm, and hypoblast cells. These layers are responsible for providing nutrients and support to the developing embryo. The extraembryonic endoderm forms the innermost layer of the yolk sac and is involved in nutrient absorption and transport. The splanchnopleuric mesoderm surrounds the endoderm and helps in the formation of blood vessels and connective tissues. The hypoblast cells are the precursor cells that give rise to the endoderm and contribute to the lining of the yolk sac.

The hypoblast cells can differentiate into the exocoelomic membrane, mesenchymal cells, extraembryonic endoderm, extraembryonic membrane, and somatopleuric cells.