Embryology Chapter 5

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Questions and Answers

What is the primary role of the prechordal plate in embryonic development?

Contributing to limb development

Facilitating forebrain induction (correct)

Assisting in heart formation

Supporting kidney formation

Which mesoderm cells migrate through the lateral edges of the primitive streak?

Chordamesoderm

Intermediate Mesoderm

Lateral Plate Mesoderm (correct)

Extraembryonic Mesoderm

What shape does the embryonic disc take as it develops?

It remains circular throughout development

It grows narrower at both ends

It develops into a cubic shape

It initially elongates, becoming broader at the cephalic end (correct)

At what point does the definitive notochord form?

After the notochordal plate detaches from the endoderm Signup and view all the answers

What significant developmental process occurs in the primitive streak until the end of the fourth week?

Continuous supply of new cells Signup and view all the answers

Which type of mesoderm contributes to the extraembryonic mesoderm?

Lateral Plate Mesoderm Signup and view all the answers

What characterizes the growth of the cephalic part of the embryonic disc?

It results from continuous migration from the primitive streak region Signup and view all the answers

What happens to the primitive streak as development progresses?

It shows regressive changes and eventually shrinks Signup and view all the answers

During which embryonic stage does the neural groove begin to form?

Neurulation Signup and view all the answers

When does the closure of the anterior neuropore typically occur?

Around day 25 Signup and view all the answers

Which region is the last to fuse during the formation of the neural tube?

Cranial region Signup and view all the answers

What characterizes the embryo at the end of the third week of development during neurulation?

Elevation of lateral edges of the neural plate Signup and view all the answers

Which statement accurately describes the process of neural tube formation?

The neural tube 'zips' up leaving both anterior and posterior neuropores open. Signup and view all the answers

What is the main event occurring during the third week of gestation?

Gastrulation Signup and view all the answers

Which layer is formed as the innermost germ layer during gastrulation?

Endoderm Signup and view all the answers

What structure begins the process of gastrulation?

Primitive streak Signup and view all the answers

Which of the following structures is NOT formed during gastrulation?

Amniotic cavity Signup and view all the answers

At what stage of embryonic development does the primitive streak become clearly visible?

15-16 days Signup and view all the answers

Which end of the primitive streak is associated with the primitive node?

Cephalic end Signup and view all the answers

What happens to the primitive streak by the end of the 4th week?

It shrinks and disappears Signup and view all the answers

Which layer is considered the outermost germ layer?

Ectoderm Signup and view all the answers

What is the role of the definitive notochord in embryonic development?

It serves as a basis for the axial skeleton. Signup and view all the answers

Where does the notochord extend cranially from?

The prechordal plate. Signup and view all the answers

What temporarily connects the amniotic and yolk sac cavities?

Neurenteric canal. Signup and view all the answers

When does the allantois begin to appear during embryonic development?

On the 16th day. Signup and view all the answers

Which structure appears at the caudal end of the embryonic disc?

Cloacal membrane. Signup and view all the answers

What is the fate of the hypoblast during the development of endoderm cells?

It is gradually replaced. Signup and view all the answers

What does the allantoenteric diverticulum extend from?

The connecting stalk. Signup and view all the answers

Which statement about the notochord is incorrect?

It forms from the cloacal membrane. Signup and view all the answers

What role does the primitive streak play during early development?

It serves as a signaling center for organ formation. Signup and view all the answers

Which of the following is NOT a consequence of abnormal nodal expression?

Hyperactivity of the mesoderm layer Signup and view all the answers

Fibroblast Growth Factor (FGF) is crucial for which of the following processes in development?

Induction of the neural plate Signup and view all the answers

Which germ layer is primarily involved in forming supportive tissues in the body?

Mesoderm Signup and view all the answers

What is the effect of BMP4 during the developmental process?

It assists in the development of the germ layers. Signup and view all the answers

Which organ is NOT mentioned as already being formed by the third week of development?

Kidneys Signup and view all the answers

What condition involves the heart being positioned on the right side of the chest?

Dextrocardia Signup and view all the answers

Nodal is primarily involved in which aspect of embryonic development?

Initiating and maintaining the primitive streak Signup and view all the answers

Study Notes

Formation of the Notochord

Endoderm cells migrate to replace hypoblast cells, leading to the proliferation of notochordal plate cells.
Notochordal plate cells detach from endoderm, forming the definitive notochord, critical for axial skeleton development.
The notochord extends cranially to the prechordal plate and caudally to the primitive pit.
Temporary connection between the amniotic and yolk sac cavities occurs at the neurenteric canal, formed at the primitive pit's indentation.
The cloacal membrane is established at the caudal end of the embryonic disc, coinciding with the formation of the allantoenteric diverticulum (allantois) around day 16.

Mesodermal Contributions

Intermediate mesoderm cells migrate through the mid streak region, contributing to forebrain induction via the prechordal plate.
Lateral plate mesoderm cells migrate from the caudal area of the streak.
Extraembryonic mesoderm arises from cells migrating at the caudalmost part of the streak.

Growth of Embryonic Disc

Initially flat and round, the embryonic disc gradually elongates with a broad cephalic and narrow caudal end.
Continuous migration of cells from the primitive streak contributes to the growth of the cephalic part, causing elongation.
The primitive streak undergoes regressive changes by the end of the fourth week, shrinking and disappearing.

Gastrulation Process

Gastrulation, occurring in the third week, results in the formation of three germ layers: endoderm, mesoderm, and ectoderm.
Formation of the primitive streak appears as a narrow groove on the epiblast surface, identifiable in a 15-16 day embryo.
The primitive node at the streak's cephalic end surrounds the primitive pit, indicating significant developmental stages.

Implications of Mesoderm Formation

Mesodermal tissue will contribute to kidneys and other organs under the influence of FGF8, BMP4, and TGF-β.
Abnormal expressions of nodal can lead to laterality defects such as situs inversus and dextrocardia.

Neurulation

Neural tube formation begins with the folding and closure of the neural plate, starting in the cervical region and progressing cranially and caudally.
Neural folds elevate, forming the neural groove, which eventually leads to the fusion of the folds in the midline, creating the neural tube.
Anterior and posterior neuropores remain open until closure, occurring around days 25 and 28, respectively.

Developmental Milestones

By the end of the third week, the neural folds have already started to approach and fuse, forming the structure of the nervous system.
The length of the embryo at 18 days is approximately 1.25 mm, with major morphological features including the primitive node and notochord evident.

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Description

This quiz covers key processes in embryology, focusing on the migration of endoderm cells and the formation of the notochord. Understand how these transformations are critical to embryonic development. Test your knowledge on cell lineage and differentiation.