Gastrulation and Notochord Formation

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Questions and Answers

What is formed by the cytotrophoblastic cells that penetrate into the syncytium?

An outer cytotrophoblast shell (correct)

A vascular network

The chorionic cavity

The umbilical cord

Which type of villi are responsible for the direct exchange of nutrients?

Free (terminal) villi (correct)

Cytotrophoblastic villi

Stem villi

Anchoring villi

What is the significance of the connecting stalk during embryo development?

It connects the embryo to the yolk sac.

It initiates heartbeat.

It becomes the umbilical cord. (correct)

It forms the placenta.

At what stage of development does the heart begin to beat, coinciding with the readiness of the villous system?

Fourth week Signup and view all the answers

What connects the placenta to where it forms on the maternal endometrium?

Decidua basalis Signup and view all the answers

What is the primary event that occurs during gastrulation in the embryo?

Establishment of all three germ layers Signup and view all the answers

During gastrulation, which structure forms at the cephalic end of the primitive streak?

Primitive node Signup and view all the answers

What is the term for the inward migration of cells during gastrulation?

Invagination Signup and view all the answers

Which growth factor is involved in the cell migration and specification during gastrulation?

Fibroblast growth factor 8 (FGF8) Signup and view all the answers

What forms the embryonic endoderm during gastrulation?

Cells that displace the hypoblast Signup and view all the answers

Which structure determines the cranial end of the embryo during the third week of development?

Prochordal plate Signup and view all the answers

What happens to the cells remaining in the epiblast after invagination occurs?

They form ectoderm Signup and view all the answers

What does the primitive streak eventually give rise to during the process of gastrulation?

Germ layers Signup and view all the answers

What is the primary function of the notochord during embryonic development?

To serve as a precursor for the axial skeleton Signup and view all the answers

At what stage does the notochordal canal communicate with the yolk sac?

When primitive pit forms Signup and view all the answers

What structure forms at the caudal end of the embryonic disc?

Cloacal membrane Signup and view all the answers

Which cells contribute to the formation of the definitive notochord?

Prenotochordal cells in the midline Signup and view all the answers

How does the notochord influence the development of the neural tube?

It induces the formation of the neural tube Signup and view all the answers

What is the significance of the allantoenteric diverticulum during embryonic development?

It extends into the connecting stalk of the yolk sac Signup and view all the answers

Which membrane is formed where ectoderm and endoderm are adherent without mesoderm?

Buccopharyngeal membrane Signup and view all the answers

What is the shape of the embryonic disc at the beginning of its development?

Flat and round Signup and view all the answers

What is the primary source of new cells during the fourth week of embryonic development?

The caudal end of the primitive streak Signup and view all the answers

At what stage does the differentiation of germ layers begin in the caudal part of the embryonic disc?

End of the fourth week Signup and view all the answers

Which structure do cells that migrate through the cranial region of the node ultimately form?

Notochord and prechordal plate Signup and view all the answers

What characterizes the tertiary villus by the end of the third week?

Differentiation into blood cells and small blood vessels Signup and view all the answers

During which week does the primitive streak show regressive changes and begin to shrink?

End of the fourth week Signup and view all the answers

What is the starting structure of the villus at the beginning of the third week?

Primary villus Signup and view all the answers

What tissue is formed from cells migrating through the lateral edges of the node?

Paraxial mesoderm Signup and view all the answers

What additional source provides extraembryonic mesoderm besides the primitive streak?

Primitive yolk sac (hypoblast) Signup and view all the answers

Study Notes

Gastrulation

Gastrulation is the process of formation of the three germ layers: ectoderm, mesoderm, and endoderm
Occurs during the third week of gestation
Begins with the formation of the primitive streak and primitive node
Primitive streak is a groove on the surface of the epiblast
Primitive node is the cephalic end of the streak with a primitive pit in its center
Epiblast cells migrate toward the primitive streak, detach, and slip beneath it, a process called invagination
Invaginated cells displace the hypoblast forming the endoderm
Cells remaining in the epiblast form ectoderm
Cells between the newly formed endoderm and epiblast form the mesoderm
FGF8 controls cell migration and specification

Notochord

The notochord is a midline structure that develops from the primitive streak
It extends from the upper end of the primitive streak to the lower end of the prochordal plate
Notochordal process forms when cells multiply in the midline between the ectoderm and endoderm
Notochordal canal forms when the primitive pit extends into the notochordal process
The notochord forms as a solid cord of cells, the definitive notochord, which underlies the neural tube
Notochord acts as a forerunner in the development of the vertebral column
Notochord induces the formation of the neural tube

Embryonic Disc Growth

The embryonic disc is initially flat and round
It gradually becomes elongated with a broad cephalic and narrow caudal end
Expansion occurs mainly by continuous migration of cells from the primitive streak in the cephalic region
Primitive streak regresses and disappears by the end of the fourth week
Differentiation of germ layers in the cephalic region begins by the middle of the third week
Differentiation of germ layers in the caudal region begins by the end of the fourth week
This causes the embryo to develop cephalocaudally

Fate Map Established During Gastrulation

Cells that ingress through the cranial region of the primitive node become prechordal plate and notochord
Cells at the lateral edges of the node and cranial end of the streak become paraxial mesoderm
Cells that migrate through the midstreak region become intermediate mesoderm
Cells migrating through the more caudal part of the streak form lateral plate mesoderm
Cells migrating through the caudal most part of the streak contribute to the extraembryonic mesoderm

Further Development of the Trophoblast

The trophoblast is characterized by primary villi that consist of a cytotrophoblastic core covered by a syncytial layer
Secondary villi form when mesodermal cells penetrate the core of primary villi
Tertiary villi (definitive placental villi) form when mesodermal cells differentiate into blood cells and blood vessels
Capillaries in tertiary villi connect with capillaries in the chorionic plate and the connecting stalk
This establishes a connection between the placenta and the embryo
Cytotrophoblastic cells in villi penetrate the syncytium and establish contact with neighboring villous stems, forming a thin outer cytotrophoblast shell
The outer cytotrophoblast shell surrounds the trophoblast, firmly attaching the chorionic sac to the maternal endometrial tissue
Stem villi extend from the chorionic plate to the decidua basalis
Free villi branch from the sides of stem villi
The connecting stalk develops into the umbilical cord

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Description

This quiz explores the processes of gastrulation and the formation of the notochord during embryonic development. Key concepts include the development of germ layers and the role of the primitive streak and nodes. Ideal for students of developmental biology.