Embryology Week 3

What end of the primitive streak is the primitive node located at?

Cranial end

What forms the primitive groove and pit?

Migrating epiblast cells

Where is the primitive pit located?

The midline of the cranial primitive streak

What type of epithelium are epiblast cells made of?

simple columnar epithelium

What connects epiblast cells to each other?

Junctional competes

What are the two zones of the desmosomes holding epiblasts together?

Zonula adherens and macula adherens

What makes up the zonula adherens?

e-cadherins

What makes up the macula adherens?

desmoglzins and desmocollins

What breaks the cadherins that make up junctional compelexes?

Transcription factor snail

What activates transcription factor snail?

High nodal levels

What two substances are produced by cadherin-free epiblasts?

Hyaluronic acid

Fibronectin

What type of molecule is hyaluronic acid?

GAG

What type of molecule is Fibronectin?

A Glycoprotein

What do the substances secreted by migrating epiblasts do?

coats the migrating epiblast and makes them slippery

Seeps down to the space between the epiblasts and hypoblast

What are migrating epiblast cells called while they are moving through the primitive streak?

Bottle cells

What are bottle cells called after they have moved underneath the primitive streak?

Mesenchymal cells

What special projection do mesenchymal cells use to crawl to their destination?

Pseudopodia

What gene tell migrating mesenchymal cells where to go?

Brachyury gene

What is the AKA of brachury gene?

T gene

What genes are activated by T gene?

Foxa-2 and goosecoid

What gene works with brachyury gene to guide migrating mesenchymal cells?

Nodal

What is the process of epiblast migration called?

ingression/ invagination

Which is the first germ layer to form?

Mesoderm

What layers does the mesoderm form between?

Hypoblast and epiblast

What is the second germ layer to form?

Endoderm

Which germ layer invades the hypoblast layer?

Endoderm

Which germ layer's cells are exposed to the highest levels of nodal?

Endoderm

Which germ layer's cells convert back to epithelium after they finish migrating?

Endoderm

What is the third germ layer to form?

Ectoderm

The formation of which germ layer completes the crude trilaminar disc?

Ectoderm

Which germ layer morphs into muscle tissue?

Mesoderm

Which germ layer morphs into epidermis, glands, and ducts?

Ectoderm

Which germ layer forms the alimentary canal?

Endoderm

What is formed by the first collection of mesoderm cells?

Prechordal plate

What is the AKA of the prechordal plate?

head organizer

Which end of the mesoderm does the prechordal plate form at?

Cranial end

The formation of what structure is induced by the prechordal plate?

Early forebrain

What gene induces the formation of the early forebrain?

Sonic hedgehog gene

What end of the embryo does the cloacal membrane form at?

Caudal end

T or F: The cloacal membrane is a part of the trilaminar disc

False (it is too tightly packed together, keeping mesoderm out and making it bilaminar)

What does the cloacal membrane develop into?

Urethra, anus, and vagina

What forms the terminal end of the gut tube?

cloacal membrane

When does the cloacal membrane finish formation?

Week 7 gestation

Which germ layers fuse cranially to form the oropharyngeal membrane?

Ectoderm and Endoderm

What does the oropharyngeal membrane develop into?

The opening of the oral cavity

When does the oropharyngeal membrane form?

Week 4 gestation

What forms the start of the foregut?

Oropharyngeal membrane

What marks the end of gastrulation?

The formation of the three germ layers

What is the name of the process by which the neural tube and notochord form?

Neuralation

When does the primitive streak begin to degenerate?

The beginning of week 4 gestation

What forms from the last remaining primitive streak in the caudal region?

Tail bud

What parts of the neural tube are formed by the tail bud?

Sacral and coccygeal parts

What is the process by which the tail bud becomes the neural tube?

Secondary neurulation

What gives rise to the sacral and coccygeal somites and neural crest cells?

Tail bud cells

What forms if the primitive streak fails to completely disappear?

Teratoma

What is the most common neoplasm in newborns?

Teratoma

T or F: Teratomas are considered germ cell tumors because it typically contains all three germ layers and their derived tissues

True

What % of teratomas are cancerous/malignant?

15%

What gender are GI complications of teratomas more common in?

Female (80%)

What is the AKA of the notochord?

Definitive notochord

When does the notochord begin development?

Week 3 gestation

T or F: The notochord is a permanent structure

False

What structures does the notochord grow between?

Primitive node and prechordal plate

What provides temporary axial support for the growing embryo?

Notochord

What structures does the notochord induce the formation of?

Neural tube

Vertebral bodies

What do the remnants of the notochord become?

Nucelus pulpous of the IVD

When do the notochord cells disappear by?

10 yo

What is the term for piled up mesenchymal cells at the prechordal plate?

Notochordal process

What are the AKAs of the no chordal process?

Head process

Immature notochord

What genes are turned off in order for migrating mesenchymal cells to become notochord cells?

Foxa-2

Brachyury

What results from failure to turn off Foxa-2 in notochord cells?

Birth defects

Why is Brachyury gene turned off in notochord cells?

Protects them as they pass through the primitive node

What direction does the primitive streak regress?

Cranial-to-caudal

What direction does the notochord elongate in?

Cranial-to-caudal

What forms from the hollowing of the notochord?

Lumen

What is the name of the lumen formed by hollowing of the notochord?

Notochordal canal

What part of the notochord enlarges?

Ventral part

What does the bottom of the notochord fuse with?

Endoderm