Podcast
Questions and Answers
What occurs when the heart begins to beat in the 4th week of development?
What occurs when the heart begins to beat in the 4th week of development?
What type of villi extend from the chorionic plate to the decidua basalis?
What type of villi extend from the chorionic plate to the decidua basalis?
What is the function of free or terminal villi?
What is the function of free or terminal villi?
By what day does the chorionic cavity become larger?
By what day does the chorionic cavity become larger?
Signup and view all the answers
What develops from the narrow connecting stalk?
What develops from the narrow connecting stalk?
Signup and view all the answers
What is the purpose of the villous system?
What is the purpose of the villous system?
Signup and view all the answers
When does the embryo become attached to its trophoblastic shell by a narrow connecting stalk?
When does the embryo become attached to its trophoblastic shell by a narrow connecting stalk?
Signup and view all the answers
What is the function of the chorionic cavity?
What is the function of the chorionic cavity?
Signup and view all the answers
What type of villi branch from the sides of stem villi?
What type of villi branch from the sides of stem villi?
Signup and view all the answers
What is the significance of the 4th week of development in terms of the villous system?
What is the significance of the 4th week of development in terms of the villous system?
Signup and view all the answers
Study Notes
Gastrulation
- Cells invaginate, displacing hypoblast to form embryonic endoderm, and some cells come to lie between epiblast and newly formed endoderm to form mesoderm.
- Remaining cells in the epiblast form ectoderm.
- The epiblast is the source of all germ layers, and cells in these layers will give rise to all tissues and organs in the embryo.
Migration of Cells
- Cells migrate beyond the margin of the disc, establishing contact with the extraembryonic mesoderm covering the yolk sac and amnion.
- In the cephalic direction, cells pass on each side of the prechordal plate and the node in a cephalic direction.
Formation of the Notochord
- Prenotochordal cells invaginate in the primitive pit, move forward, and reach the prechordal plate.
- As the hypoblast is replaced by endoderm cells, cells of the notochordal plate proliferate and detach from the endoderm, forming a solid cord of cells, the definitive notochord.
- The notochord underlies the neural tube and serves as the basis for the axial skeleton.
Growth of the Embryonic Disc
- The primitive streak shows regressive changes, rapidly shrinks, and soon disappears by the end of the 4th week.
- The primitive streak at the caudal end of the disc continues to supply new cells until the end of the 4th week.
- Germ layers begin their specific differentiation by the middle of the 3rd week in the cephalic part, and by the end of the 4th week in the caudal part.
Teratogenesis Associated with Gastrulation
- The beginning of the 3rd week of development is a highly sensitive stage for teratogenic insult.
- Fate maps can be made for various organ systems, which may be damaged by teratogens.
- This stage is reached 2 weeks after fertilization, approximately 4 weeks from the last menses.
Further Development of the Trophoblast
- By the beginning of the 3rd week, the trophoblast is characterized by primary villi consisting of a cytotrophoblastic core covered by a syncytial layer.
- Mesodermal cells penetrate the core of primary villi and grow toward the decidua, forming secondary villi.
- By the end of the 3rd week, mesodermal cells in the core of the villus begin to differentiate into blood cells and small blood vessels, forming the villous capillary system.
Development of the Placenta
- The villus is now known as a tertiary villus or definitive placental villus.
- Capillaries in tertiary villi make contact with capillaries developing in mesoderm of the chorionic plate and in the connecting stalk.
- These vessels establish contact with the intraembryonic circulatory system, connecting the placenta and the embryo.
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Related Documents
Description
Learn about the process of gastrulation, including the formation of embryonic endoderm, mesoderm, and ectoderm from the epiblast, and how these germ layers give rise to tissues and organs.
