Gastrulation: Formation and Migration
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Questions and Answers

What primary process occurs during gastrulation?

  • Formation of ectoderm and endoderm
  • Formation of mesoderm and endoderm
  • Formation of all three germ layers (correct)
  • Differentiation of the amniotic cavity

Which statement best describes the primitive streak?

  • It is clearly visible at day 10 of embryonic development.
  • It is established at the cephalic end of the embryo.
  • It is a structure that forms on the surface of the hypoblast.
  • It is a narrow groove appearing on the surface of the epiblast. (correct)

What is the significance of fibroblast growth factor 8 (FGF8) during gastrulation?

  • It promotes the development of the ectoderm layer.
  • It regulates cell specification into the mesoderm. (correct)
  • It controls the outward movement of cells from the epiblast.
  • It initiates the formation of the amnion.

What happens to the epiblast cells upon reaching the primitive streak?

<p>They become flask-shaped and detach. (B)</p> Signup and view all the answers

At what embryonic stage is the primitive streak clearly visible?

<p>Around 15 to 16 days of development (A)</p> Signup and view all the answers

What role do cells play in the formation of the embryonic endoderm during gastrulation?

<p>They displace the hypoblast to create the embryonic endoderm. (B)</p> Signup and view all the answers

Which germ layer is derived from cells that remain in the epiblast after gastrulation?

<p>Ectoderm (B)</p> Signup and view all the answers

What is the primary function of the prechordal plate during gastrulation?

<p>It induces the development of the forebrain. (A)</p> Signup and view all the answers

How do cells migrate during gastrulation?

<p>They establish contact with the extraembryonic mesoderm and migrate cranially. (D)</p> Signup and view all the answers

What characterizes the oropharyngeal membrane in relation to the embryonic development?

<p>It represents the future opening of the oral cavity. (B)</p> Signup and view all the answers

What is the first structure formed by the prenotochordal cells during notochord formation?

<p>Notochordal plate (C)</p> Signup and view all the answers

Which layer is NOT formed during the advanced stage of embryonic development at 14-15 days?

<p>Pericardium (C)</p> Signup and view all the answers

How does the notochord grow during development?

<p>Dynamic growth with cranial followed by caudal formation (D)</p> Signup and view all the answers

What is the primary function of the notochord in vertebrate development?

<p>Inducing the axial skeleton (B)</p> Signup and view all the answers

What is the role of the allantois in human development?

<p>It remains rudimentary and may affect bladder development (A)</p> Signup and view all the answers

What connects the amniotic and yolk sac cavities during embryonic development?

<p>Neurenteric canal (C)</p> Signup and view all the answers

What does the cloacal membrane primarily consist of?

<p>Ectoderm and endoderm cells tightly adherent (A)</p> Signup and view all the answers

At what stage do definitive endoderm and differentiation of mesoderm occur?

<p>16 days (B)</p> Signup and view all the answers

Flashcards

Gastrulation

The process of forming the three germ layers: ectoderm, mesoderm, and endoderm. It begins with the formation of the primitive streak on the epiblast, where cells migrate towards and detach from the epiblast to form the mesoderm and endoderm.

Primitive Streak

A structure that forms during gastrulation. It is a thickened band of cells on the epiblast. Cells migrate towards the primitive streak, detach from the epiblast, and move underneath it to form the mesoderm.

Epiblast

The layer of cells on the surface of the embryo that forms the ectoderm.

Endoderm

The innermost layer of the embryo, formed during gastrulation. It will give rise to the lining of the digestive tract.

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Mesoderm

The middle layer of the embryo, formed during gastrulation. It will give rise to tissues like muscle, bone, and blood.

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Migrating Cells

Cells that migrate between the epiblast and hypoblast layers during gastrulation, extending laterally and cranially to the disc margin.

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Prechordal Plate

A structure that forms between the notochord tip and the oropharyngeal membrane. It is derived from cells migrating through the node in the midline and is important for forebrain induction.

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Oropharyngeal Membrane

A membrane situated at the cranial end of the embryonic disc, consisting of ectoderm and endoderm cells. It marks the future opening of the oral cavity.

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Notochord

The central axis of the embryo formed during gastrulation. It is crucial for inducing the axial skeleton and extends cranially to the prechordal plate and caudally towards the primitive pit.

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Primitive pit

A small indentation in the epiblast, forming a temporary connection between the amniotic and yolk sac cavities through the neurenteric canal.

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Allantois

A small diverticulum that appears on the posterior wall of the yolk sac around the 16th day. It extends into the connecting stalk and may play a role in bladder development abnormalities.

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Cloacal Membrane

Situated at the caudal end of the embryonic disc, it is a membrane similar to the oropharyngeal membrane, consisting of tightly adherent ectoderm and endoderm cells.

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Prenotochordal Cells

Cells that migrate from the node during notochord formation. They intercalate in the hypoblast, forming a two-layered notochordal plate before separating to form the definitive notochord.

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Notochordal Plate

The temporary two-layered structure formed by prenotochordal cells intercalating in the hypoblast. It later detaches from the endoderm to form the definitive notochord.

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Definitive Notochord

The definitive notochord that arises from detaching from the endoderm. It plays a vital role in axial skeleton formation and serves as a signaling center during development.

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Hypoblast

A layer of cells below the epiblast that contributes to the formation of the yolk sac. It is involved in the early stages of embryonic development.

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Connecting Stalk

The connection between the embryo and the placenta, which contains blood vessels that connect the embryo to the mother.

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Study Notes

Gastrulation

  • The process of forming the mesoderm and endoderm.
  • Begins with the formation of the primitive streak on the epiblast.
  • Involves cells migrating towards the primitive streak, where they become flask-shaped, detach from the epiblast, and move underneath it.
  • Controlled by fibroblast growth factor 8 (FGF8), synthesized by streak cells themselves, which controls cell specification into the mesoderm.
  • Results in the formation of the three germ layers: ectoderm, mesoderm, and endoderm.

Cell Migration During Gastrulation

  • Cells move between the epiblast and hypoblast layers.
  • Spread laterally and cranially, extending beyond the disc margin.
  • Establish contact with extraembryonic mesoderm covering the yolk sac and amnion.
  • Migrate in the cephalic direction, passing along each side of the prechordal plate.

Prechordal Plate

  • Forms between the notochord tip and the oropharyngeal membrane.
  • Derived from cells migrating through the node in the midline.
  • Crucial for forebrain induction.

Oropharyngeal Membrane

  • Situated at the cranial end of the disc.
  • Consists of closely adhering ectoderm and endoderm cells.
  • Represents the future opening of the oral cavity.

Notochord Formation

  • Begins with prenotochordal cells originating from the primitive node and moving cranially to the prechordal plate.
  • Prenotochordal cells intercalate in the hypoblast, forming a two-layered notochordal plate for a short time.
  • Notochordal plate cells detach from the endoderm to form the definitive notochord.
  • Serves as an important signaling center for inducing the axial skeleton.
  • Grows dynamically from cranial to caudal.
  • Extends from the prechordal plate cranially and caudally to the primitive pit.
  • The primitive pit forms an indentation in the epiblast, temporarily connecting the amniotic and yolk sac cavities through the neurenteric canal.

Cloacal Membrane

  • Forms at the caudal end of the embryonic disc.
  • Similar in structure to the oropharyngeal membrane, consisting of tightly adherent ectoderm and endoderm cells, with no intervening mesoderm.
  • When the cloacal membrane forms, the posterior wall of the yolk sac develops a small diverticulum (allantois) that goes into the connecting stalk.
  • The allantois, a diverticulum that appears around the 16th day, may play a role in bladder development abnormalities.

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Description

This quiz focuses on the intricate processes of gastrulation, including the formation of mesoderm and endoderm during embryonic development. It covers the role of the primitive streak, cell migration, and the formation of germ layers. Test your understanding of these fundamental concepts in developmental biology.

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