Embryology: Cytotrophoblast and Germ Layers

Questions and Answers

What structure do somitomeres in the cephalic region contribute to during the second week of development?

Axial skeleton

Excretory units

Dermis formation

Head mesenchyme (correct)

At what stage do the first pair of somites appear in embryonic development?

Approximately at the twentieth day (correct)

Start of the third week

End of week five

End of the second week

What component do myotomes provide for embryonic segments?

Neural tissue

Dermal tissue

Skeletal tissue

Musculature (correct)

What type of tissue do the cells from the ventral and medial walls of somites become after differentiation?

Mesenchyme Signup and view all the answers

How many pairs of somites are typically present at the end of week five of development?

42-44 pairs Signup and view all the answers

Which part of the somite gives rise to the dermatome?

Dermomyotome Signup and view all the answers

Which of the following structures is formed along with the parietal mesoderm?

Lateral and ventral body walls Signup and view all the answers

What does the intermediate mesoderm eventually develop into?

Excretory units of the urinary system Signup and view all the answers

What does the visceral mesoderm contribute to in early embryonic development?

The formation of blood cells and blood vessels Signup and view all the answers

What is primarily responsible for the gastro-intestinal tract formation?

Endodermal germ layer Signup and view all the answers

During which weeks is the growth in length of the fetus particularly striking?

Weeks 3-5 Signup and view all the answers

What happens to the proportional size of the head during fetal growth?

It grows less than the rest of the body Signup and view all the answers

What are the serous membranes formed by the visceral mesoderm that line the cavities?

Thin serous membranes Signup and view all the answers

Which derivative is NOT formed from ectoderm?

Epithelial components of the trachea Signup and view all the answers

Which of the following structures is derived from the mesoderm?

Dermis of skin Signup and view all the answers

Which of the following is a derivative of the endoderm?

Liver Signup and view all the answers

What is a congenital malformation?

A gross structural defect present at birth Signup and view all the answers

Which structure is NOT derived from the neuroectoderm?

Spinal ganglia Signup and view all the answers

Which of the following is formed from the surface ectoderm?

Epidermis Signup and view all the answers

What does the mesoderm contribute to in terms of organ development?

Muscles of viscera Signup and view all the answers

Which of these structures is formed from the intermediate plate of the mesoderm?

Urogenital system Signup and view all the answers

What is the function of the cytotrophoblast in early development?

It consists of mononucleated cells providing nutrients. Signup and view all the answers

Which layer of cells is adjacent to the blastocyst cavity and forms part of the bilaminar germ disc?

Hypoblast Signup and view all the answers

What defines the syncytiotrophoblast in early embryonic development?

It is multinucleated without distinct cell boundaries. Signup and view all the answers

What significant event occurs during the third week of development?

Gastrulation establishing three germ layers. Signup and view all the answers

What is Heuser's membrane also known as?

Exocoelomic membrane Signup and view all the answers

Which germ layer is composed of high columnar cells?

Epiblast Signup and view all the answers

What does the extraembryonic mesoderm develop into?

Chorionic plate and coeloms Signup and view all the answers

Which of the following describes the newly formed secondary yolk sac?

It is smaller than the primary yolk sac. Signup and view all the answers

What is the condition of the anterior and posterior neuropores by day 27?

Both neuropores are closed Signup and view all the answers

What process takes place when neural crest cells migrate from the neuroectoderm?

Epithelial to mesenchymal transition Signup and view all the answers

At what approximate day does the closure of the anterior neuropore occur?

Day 25 Signup and view all the answers

What are the two ectodermal thickenings visible in the cephalic region during development?

Lens placode and otic placode Signup and view all the answers

What structure is formed from the otic placode during development?

Otic vesicle Signup and view all the answers

What characterizes the broader part of the central nervous system after neurulation is complete?

Brain vesicles Signup and view all the answers

What is the significance of paraxial mesoderm during development?

It contributes to somite formation Signup and view all the answers

What happens to the mesoderm layer between day seventeen and day twenty in development?

It becomes denser and thicker Signup and view all the answers

Study Notes

Germ Layers and Early Development

Cytotrophoblast is the inner layer of mononucleated cells.
Syncytiotrophoblast forms the outer layer of multinucleated cells without distinct boundaries.
Embryoblast (inner cell mass) differentiates into two layers:
- Hypoblast: Small cuboidal cells next to the blastocyst cavity.
- Epiblast: High columnar cells adjacent to the amniotic cavity.
Together, the hypoblast and epiblast form the bilaminar germ disc.

Extraembryonic Structures

Amniotic cavity develops from a small cavity within the epiblast, lined with amnioblasts.
Heuser's membrane (exocoelomic membrane) forms from hypoblast cells, lining the cytotrophoblast and creating the exocoelomic cavity (primitive yolk sac).
By day eleven, the blastocyst is embedded in the endometrial stroma.
Extraembryonic mesoderm forms, creating spaces that divide it into splanchnopleuric (facing exocoelomic membrane) and somatopleuric (facing cytotrophoblast) layers.
On day thirteen, migration of hypoblast cells creates a secondary yolk sac, smaller than the primary, with remnants forming exocoelomic cysts.

Gastrulation and Trilaminar Germ Disc Formation

Gastrulation in the third week establishes all three germ layers.
Key structures observed include the neural fold, primitive node, primitive streak, somite, and neural groove during embryonic development.
The neural tube closes between days 25 and 27, marking the completion of neurulation.
Neural crest cells dissociate from neuroectoderm and migrate into mesoderm.

Development of Ectoderm

Otic placode and lens placode develop into auditory and visual structures respectively.
Paraxial mesoderm thickens and segments into somites, forming head mesenchyme and forming the axial skeleton.
Somites differentiate into:
- Sclerotome: Surrounds the spinal cord, forming the vertebral column.
- Dermomyotome: Forms myotomes (musculature) and dermatomes (dermis).

Mesoderm and Germ Layer Derivatives

Mesoderm differentiates into visceral (splanchnic) and parietal (somatic) components, forming body walls and gut linings.
Intermediate mesoderm becomes excretory units of the urinary system.
Blood vessels originate from mesoderm cells in the yolk sac, linking the embryo to the placenta.

Endoderm Development

Endoderm primarily forms the gastrointestinal tract through lateral folding, incorporating portions of the yolk sac.
Organ systems established by the second month include significant features recognizable in the embryo.

Fetal Growth Period

The fetal period spans week 9 to birth, characterized by rapid growth and organ maturation.
Head growth slows significantly compared to body growth as the fetus develops.

Germ Layer Derivatives

Ectoderm results in structures such as:
- Neural crest: Spinal and autonomic ganglia, bones of the skull, melanocytes.
- Surface ectoderm: Epidermis, hair, nails, salivary glands.
- Neuroectoderm: Central nervous system, retina, posterior pituitary.
Mesoderm differentiates into:
- Urogenital structures and visceral components.
- Connective tissue and muscle systems.
Endoderm forms epithelial components for the trachea, digestive tract, liver, and more.

Congenital Malformations

Defined as gross structural defects present at birth, highlighting the significance of proper embryonic development.

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Description

This quiz explores the key concepts of embryonic development, focusing on the cytotrophoblast and syncitiotrophoblast structures. It also covers the differentiation of the embryoblast into the hypoblast and epiblast layers. Test your understanding of these foundational concepts in developmental biology.