Embryology Chapter 5: Gastrulation

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Questions and Answers

What role does the primitive streak play in embryogenesis?

It defines the endpoint of cell migration.

It allows for the differentiation of ectoderm layers.

It is responsible for establishing the body axes of the embryo. (correct)

It serves as the site for early embryonic organ development.

What is the primary role of Hensen's node in early embryo development?

It creates the outer layer of the ectoderm.

It is responsible for the digestion of maternal nutrients.

It serves as a signaling center for mesoderm differentiation. (correct)

It induces the formation of the neural tube.

Which statement accurately describes Hensen's node?

It is equivalent to the organizer in amphibian development. (correct)

It generates signals that lead to the formation of epithelial tissue.

It marks the location for endoderm cell migration.

It is located at the caudal end of the primitive streak.

How do cells in the epiblast prepare to migrate through the primitive streak?

By undergoing an Epithelial to Mesenchymal Transition (EMT). Signup and view all the answers

What occurs during the first wave of cell migration through the primitive streak?

Cells insert themselves into the hypoblast layer to form the endoderm. Signup and view all the answers

What characterizes the mesenchyme during gastrulation?

It features loosely arrayed tissues with a substantial amount of matrix. Signup and view all the answers

Which of the following describes the process by which cells migrate during the formation of the primitive streak?

Cells undergo apical-basal polarity changes and transition to a mesenchymal state. Signup and view all the answers

What is the consequence if migratory streak cells fail to lose E-cadherin during EMT?

Disruption of the migratory movements of these cells. Signup and view all the answers

What spatial organization is primarily established at the formation of the primitive streak?

The anterior-posterior body axis of the embryo. Signup and view all the answers

What happens to cells that undergo a Mesenchymal to Epithelial Transition (MET) during development?

They transform back into an epithelial layer from a migratory state. Signup and view all the answers

What characterizes the cadherin family members involved in cell migration during embryogenesis?

They differ in binding properties, affecting cell segregation. Signup and view all the answers

How often do somites form in mouse embryos during development?

Every 2 hours. Signup and view all the answers

What is a likely outcome if the cadherin expression is significantly altered during embryonic development?

Improper spatial segregation leading to developmental abnormalities. Signup and view all the answers

What is a key function of the cells migrating through the primitive streak?

To contribute to the notochord and mesodermal structures. Signup and view all the answers

What determines the location of the primitive streak within the embryonic disc?

Unique yet unidentified signals guide its positioning within the disc. Signup and view all the answers

What is the main type of cellular transition involved when epiblast cells migrate through the primitive streak?

Epithelial to Mesenchymal Transition (EMT). Signup and view all the answers

What is the primary role of the hypoblast in early embryonic development?

To line the interior of the blastocoel Signup and view all the answers

Which statement best describes the function of cadherins in epithelial cells?

They aid in cell adhesion and formation of adherens junctions. Signup and view all the answers

Which cells will ultimately make up the entire embryo?

Epiblast cells Signup and view all the answers

What is the characteristic arrangement of epithelial cells in early embryonic development?

They are tightly linked with little intercellular space. Signup and view all the answers

What is the significance of Hensen's node during body axis establishment?

It plays a role in organizing axial structures. Signup and view all the answers

What process allows epithelial cells to change into a more motile mesenchymal form during development?

Epithelial to mesenchymal transition (EMT) Signup and view all the answers

What is true regarding the relationships between epithelial cells and their extracellular matrix?

Epithelial cells have little extracellular matrix. Signup and view all the answers

Which statement accurately describes the cells of the trophoblast?

They assist in forming the extraembryonic membranes. Signup and view all the answers

Study Notes

Chapter 5: Gastrulation; establishment of embryonic germ layers and early patterning

Key terms: Axis specification, body axes, cilia, pattern formation, blastocyst (blastula), hypoblast, inner cell mass, trophoblast (trophectoderm), embryonic germ layers (mesoderm, endoderm, ectoderm), gastrula, gastrulation, E-cadherin, mesenchyme, mesenchymal, epithelial cells, epithelium, epithelial-mesenchymal transition (EMT), notochord, anterior/posterior, dorsal/ventral, extra-embryonic tissues (membranes), prechordal plate, primitive node, primitive streak, cloacal membrane, buccopharyngeal membrane

Learning Objectives

Name the three germ layers of the embryo established during gastrulation and give two examples of adult tissues that arise from each.
Describe "axis specification" and give an example of axis specification occurring during gastrulation.
Identify the embryonic germ layer that gives rise to the notochord and describe its role in early development.
Explain the process of establishing right/left body axis patterning, including the role of cilia.
Differentiate between mesoderm and mesenchyme.
Describe the epithelial-mesenchymal transition (EMT) and name one important molecule in this transition.
Explain the importance of "pattern formation" in embryogenesis and describe potential consequences of abnormal patterning.

Gastrulation

Gastrulation is a stage of embryonic development where the embryo establishes the three germ layers (endoderm, ectoderm, and mesoderm) that will form all adult tissues.
Body axes (cranial/caudal, left/right, dorsoventral) are patterned during gastrulation.
Morphogenesis is the process of structure building, occurring during gastrulation.
Initially, the embryo consists of the inner cell mass and trophoblast/trophectoderm.
Inner cell mass cells migrate to the underside of the embryonic disc, detaching and forming the hypoblast (later endoderm).
Hypoblast expands to line the blastocoel/yolk sac.
The epiblast cells form the remaining embryo.
Cadherins are cell adhesion molecules that help establish tissue structure and are important in gastrulation.

Gastrulation-Cells Migrate

Cells of the inner cell mass migrate, detach from the disc, arrange into a sheet (hypoblast), expanding to form the interior of the blastocoel(yolk sac)
Scattered cells migrate to the underside of the disc, detach, and arrange themselves into a sheet called the hypoblast.
The hypoblast will later become the endoderm.
The remaining cells of the inner cell mass are called the epiblast and these form the embryo.

Cell Migration into Primitive Streak

Epiblast cells migrate towards the midline forming a groove called the primitive streak.
Cells lose epithelial characteristics and become migratory through an epithelial-to-mesenchymal transition (EMT), driven by the loss of E-cadherin.

Formation of Notochord and Prechordal Plate

The notochord is a mesodermal structure crucial for vertebrate development.
Mesodermal cells from Hensen's node migrate cranially forming the notochord.
Notochord runs along the midline, between the ectoderm and endoderm.
Prechordal plate is mesoderm cranial to the notochord, and important for head development.
It forms at the cranial end of the embryo.

Buccopharyngeal and Cloacal Membranes

These membranes are formed by the fusion of ectoderm and endoderm.
These membranes separate the digestive tube from the external environment at the mouth and anus. (later degenerate).

Completion of Gastrulation

The embryonic disc, at this point, has three germ layers: ectoderm, mesoderm, and endoderm.
Body axes have been established.

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Description

Test your knowledge on gastrulation and the establishment of embryonic germ layers with this quiz. You'll explore key terms, axis specification, and the roles of various cells during this critical phase of embryonic development. Perfect for students studying developmental biology and embryology.