Embryology Chapter on Embryonic Disc Development

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Questions and Answers

What is the initial shape of the embryonic coelom?

Horseshoe (correct)

Circular

Elliptical

Triangular

How does the yolk sac change during development?

It becomes smaller and is lined by cubical cells. (correct)

It enlarges significantly.

It transforms into the amniotic cavity.

It remains constant in size.

What does the intra-embryonic coelom communicate with during development?

Neural groove

Yolk sac

Extra-embryonic coelom (correct)

Amniotic cavity

What happens to the head and tail folds of the embryonic disc during development?

They remain close together. Signup and view all the answers

What is the term for the cavity formed from the intra-embryonic mesoderm?

Intra-embryonic coelom Signup and view all the answers

How are the halves of the embryonic coelom positioned?

On either side of the midline Signup and view all the answers

What is the appearance of the embryonic coelom at first?

Closed cavity Signup and view all the answers

What does the notochord develop into as the embryo enlarges?

Notochordal canal Signup and view all the answers

Which structure becomes lined by cubical cells during the embryonic development process?

Secondary yolk sac Signup and view all the answers

What part of the notochord persists in the intervertebral discs?

Nucleus pulposus Signup and view all the answers

Which of the following structures does the notochordal canal communicate with?

Yolk sac Signup and view all the answers

What occurs to the floor of the notochordal canal during development?

It begins to break down and create openings Signup and view all the answers

What is formed after the walls of the notochordal canal become flattened?

Notochordal plate Signup and view all the answers

Which structure does the notochord not contribute to?

Vertebral column Signup and view all the answers

What is the primary role of the cells forming the floor of the notochordal canal?

To separate the canal from the cavity of the yolk sac Signup and view all the answers

How does the yolk sac relate to the notochordal canal during development?

It is connected by a canal Signup and view all the answers

What structure forms from the thickened part of the cranial end of the primitive streak?

Notochord Signup and view all the answers

During the development of the notochord, which structure is formed first?

Blastopore Signup and view all the answers

In which region does the primitive knot multiply and form structures?

Cranially in the middle line Signup and view all the answers

What is the final outcome of the rearrangement of cells in the notochordal process?

Creation of a solid rod called the notochord Signup and view all the answers

Where does the notochordal process develop in relation to the ectoderm?

Deep to the ectoderm Signup and view all the answers

What structure does the notochord become a part of at the early stages of embryonic development?

Supporting the development of the central nervous system Signup and view all the answers

Which embryonic structure does the notochord lie cranially to?

Prochordal plate Signup and view all the answers

What is the term used for the initial formation of the notochord that follows the blastopore development?

Notochordal process Signup and view all the answers

What characterizes the definitive notochord during its formation?

It forms a solid rod of cells. Signup and view all the answers

Which of the following statements about the notochord is true?

It can persist into adult life in some chordates. Signup and view all the answers

During the process of neurulation, where does the neural tube develop?

Overlying the notochord. Signup and view all the answers

What is the initial shape of the notochordal plate before it becomes curved?

Flat. Signup and view all the answers

What is the relationship between the definitive notochord and the endoderm?

The notochord is completely separated from the endoderm. Signup and view all the answers

In which stage of development does the notochord appear?

During the embryonic development. Signup and view all the answers

What part of the developing embryo does the neural tube extend from?

The prochordal plate. Signup and view all the answers

Which of these structures is formed from the neural tube?

The spinal cord. Signup and view all the answers

What structure does the cranial part of the neural tube develop into?

Brain Signup and view all the answers

What is the depression called that is located between the developing brain and pericardium?

Stomodaeum Signup and view all the answers

What occurs to the primitive streak towards the tail end of the embryo?

It disappears Signup and view all the answers

Which germ layer derivatives are primarily found in sacrococcygeal tumours?

All three germ layers Signup and view all the answers

What is the main role of the notochord in the process of neural tube formation?

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

At what developmental day does the primitive streak appear?

Day 15 Signup and view all the answers

Which structure is seen in the cardiogenic area by day 17 of embryonic development?

Heart tube Signup and view all the answers

What role does Wharton's jelly play in embryonic development?

Rich in proteoglycans Signup and view all the answers

What is the function of the vitello-intestinal duct during embryonic development?

It connects the gut to the yolk sac. Signup and view all the answers

Which region is referred to as the foregut in embryonic development?

The part of the gut cranial to the vitello-intestinal duct. Signup and view all the answers

What surrounds the embryo as the amniotic cavity expands?

Ectodermal tissue. Signup and view all the answers

What is formed as the embryo undergoes folding during development?

Lateral folds. Signup and view all the answers

What is the structure that becomes elongated during prenatal development before disappearing?

The vitello-intestinal duct. Signup and view all the answers

Which of the following statements accurately describes the umbilical opening?

It is a result of the lateral folds closing around the embryo. Signup and view all the answers

During which stage does the amniotic cavity surround the embryo?

As the embryonic disc folds on itself. Signup and view all the answers

What type of tissue primarily makes up the ectoderm in the developing embryo?

Epithelial tissue. Signup and view all the answers

Study Notes

Further Development of the Embryonic Disc

The cranial end of the primitive streak enlarges to form the primitive knot.
Cells from the primitive knot multiply and travel cranially, forming a notochordal process.
The notochordal process transitions to a canal, then a plate, and finally a rod-like structure (notochord).
Most of the notochord disappears, with remnants forming the nucleus pulposus of intervertebral discs.
Ectoderm overlaying the notochord thickens, forming the neural plate, the precursor to the brain and spinal cord.
Intra-embryonic mesoderm subdivides into paraxial, intermediate, and lateral plate mesoderm.
The lateral plate mesoderm develops a cavity (intraembryonic coelom), which splits into somatopleuric and splanchnopleuric layers.
The intra-embryonic coelom gives rise to the pericardial, pleural, and peritoneal cavities.
The embryonic disc flattens, then undergoes folding (head and tail folds, lateral folds).
The endoderm is converted into a tube (gut), divided into foregut, midgut, and hindgut
The gut closes cranially at the buccopharyngeal membrane and caudally at the cloacal membrane.
The umbilical cord forms from the connecting stalk, containing umbilical arteries, vein and yolk sac remains.
The allantoic diverticulum emerges from the yolk sac before gut formation, becoming a hindgut diverticulum post-tail fold formation
The pericardial cavity, developing cranially to the prochordal plate, encloses the heart.
The septum transversum, a structure of intraembryonic mesoderm lies cranial to the pericardium and plays a role in diaphragm and liver development.

Formation of the Notochord

The notochord develops in the region between the primitive streak and prochordal plate.
The cranial end of the primitive streak thickens into the primitive knot (or node).
A depression, called the blastopore, forms in the center of the primitive knot.
Cells from the primitive knot migrate cranially, forming a solid notochordal cord (between ectoderm and endoderm).
The notochordal cord becomes a notochordal canal then a notochordal plate before becoming a solid rod.

Formation of the Neural Tube

The process of neurulation forms the neural tube, which gives rise to the brain and spinal cord.
The neural tube is derived from ectoderm located above the notochord.
The neural tube forms from the prochordal plate to the primitive knot.
Neural tube is initially continuous before differentiating into cranial (brain) and caudal (spinal cord) parts.

Subdivisions of Intra-embryonic Mesoderm

The intra-embryonic mesoderm differentiates into paraxial, intermediate, and lateral plate mesoderm.
Paraxial mesoderm segments into somitomeres, which develop into somites.
Somites will become important in the development of vertebrae, ribs, and muscles.

Formation of the Intraembryonic Coelom

Small cavities appear in the lateral plate mesoderm, coalescing to form the intra-embryonic coelom.
The intra-embryonic coelom has a horseshoe shape.
The coelom splits the lateral plate mesoderm into somatopleuric (ectoderm-facing) and splanchnopleuric (endoderm-facing) layers.
The coelomic cavity is important in forming pericardial, pleural, and peritoneal cavities.

Yolk Sac and Folding of the Embryo

The yolk sac develops in the extraembryonic region .
The yolk sac communicates with the gut.
Folding of the embryo occurs during head and tail formation
Parts of the yolk sac become enclosed within the embryo during folding.

Formation of the Umbilical Cord

The umbilical cord develops from the connecting stalk.
Blood vessels (2 arteries, 1 vein) connect the embryo to the placenta.
Wharton's jelly (gelatinous substance) surrounds the umbilical vessels, providing protection.
The umbilical cord connects the embryo to the placenta.

Allantoic Diverticulum

The allantoic diverticulum arises from the yolk sac.
It grows into the mesoderm of the connecting stalk, and gradually becomes part of the hindgut.
This structure plays a role in the formation of the urinary bladder.

Effect of Head and Tail Folds on Structures

The head and tail folds position structures, such as the pericardium, pericardial cavity, heart, prochordal plate, neural plate, and cloacal membrane
The folds determine the relationships of structures in the developing embryo.

Timeline of Events

The primitive streak is visible by day 15
Notochordal processes develop by day 17
The definitive yolk sac develops by day 17
Heart tube forms by day 19
Allantoic diverticulum forms by day 19
Intra-embryonic mesoderm forms by day 21
Neural groove and head fold formation starts by day 21
Neural tube closure occurs by day 23

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Description

This quiz covers the important stages in the further development of the embryonic disc. Key topics include the formation of the primitive knot, notochord development, and the differentiation of mesodermal layers. Understand the transformations leading to the establishment of the neural plate and the embryonic coelom.