Embryo MT2

What is the most common neoplasm in newborns?

Teratoma

Where is the most common place for teratoma to form?

Sacrococcygeal region

What type of tumor is a teratoma?

Germ cell tumor - has all three layers of germ cells

Can teratomas be treated with chemo?

Generally resistant to chemo

What might lead to a small bowel obstruction or urinary tract obstruction?

Teratoma

Are teratomas more common in females or males?

Females

When does prechordal plate formation occur?

Week 3

Where is the prechordal plate found?

Cranial portion between epiblasts and hypoblasts

What is created in the first wave?

Prechordal plate

The mesenchymal epiblasts cells that will become the prechordal plate pass through what first?

Primitive node

Where does the migration stop of the mesenchymal epiblasts cells that will form the prechordal plate?

Cranial end near AVE cells OR just caudal to area that will become oropharyngeal membrane (mouth)

What germ layer makes up the prechordal plate?

Mesoderm

What is formed in the second wave?

Notochord

Is Nodal turned on where the prechordal plate forms?

NO

What is the predominant gene secreted by the prechordal plate?

Sonic hedgehog gene

What does the sonic hedgehog gene induce?

Early forebrain

When does the cloacal membrane form?

Week 3 - same as prechordal plate

Where does the cloacal membrane form?

Caudally in the midline

What two cells grow together to form the cloacal membrane?

Epiblasts and hypoblast

What could we say the cloacal membrane is made of?

Modified ectoderm and endoderm

Is there mesoderm found between the cloacal membrane?

NO

The cloacal membrane is a ________ formed in the _______?

Bilaminar plate; trilaminar disc

Is the mesoderm part of the cloacal membrane or oropharyngeal membrane?

NO

What is the floor of the primitive node?

Amniotic cavity

What does the cloacal membrane form?

Opening to urethra, anus, and vagina around wk 7

The cloacal membrane is considered the end of what?

Gut tube

When does the oropharyngeal membrane form?

Wk 3

What two cells fuse together to make the oropharyngeal membrane and where does this happen?

Epiblasts And hypoblasts

Cranially

What is the start of the foregut?

Oropharyngeal membrane

When is gastrulation complete?

When we have the primitive streak and the 3 germ layers

Specifically where does the oropharyngeal membrane form?

just cranially to prechordal plate

What structure does the nucleus pulposus derive from?

Remnants of the notochord

Aka for notochord?

Definitive notochord

When does notochord form?

Later part of week 3

Is the primitive streak and notochord permanent structures?

NO

What develops in place of the primitive streak regressing?

Notochord

What malignant structure can develop if the notochord does not properly degenerate?

Chordoma

what is a defining feature of all vertebrates?

Notochord

The notochord grows between ______ and ______ and pushes _____ to the side?

Ectoderm and endoderm; mesoderm

Notochord grows between what two structures?

Primitive node and prechordal plate

What are the 4 functions of the notochord?

1) provide temporary axial mechanical support for growing embryo

2) help induce formation of neural tube

3) induce formation of vertebral bodies

4) formation of nucleus pulposus

Which direction does the notochord mainly elongate?

Caudal to cranial

Which direction does the primitive streak regress?

Cranial to caudal direction

What two cells must be turned on to create notochord cells and what do those genes do?

Foxa-2: turn on to avoid birth defects

Brachyury gene: protects pre-notochord cells as they pass through primitive node (like bottle cells)

How is the neurenteric canal formed?

Small region of endoderm cells close to primitive node degenerate away

What is the hollowed out lumen of the notochord called?

Notochord canal

Is the notochord tube a permanent structure?

NO- it’s short lived

What part of the notochord begins to degenerate first?

Ventral notochord (ectoderm side)

Degeneration of the endoderm during notochord canal formation creates a connection between what structures?

Notochordal canal

Secondary yolk sac

Amniotic cavity

The notochord canal becomes known as the ?

Neurenteric canal -short lived

Fluids from what two cavities will mix with the creation of the neurenteric canal?

Secondary yolk sac fluid and amniotic fluid

What cells will repopulate to close the neurenteric canal?

Endoderm cells

How do endoderm cells close the hole of the neurenteric canal?

They collapse toward the bottom

What structure is formed by endoderm collapse after the neurenteric canal is formed?

Notochordal plate

What direction does the flat Notochordal plate expand?

Laterally via mitosis

What gene induces the flat Notochordal plate to being forming a tube?

Shroom gene

In what layer does Notochordal plate and canal form?

Mesoderm

Once the Notochordal cells have regrown after the collapse, they fuse together and form a?

Temporary Notochordal tube

What fills in the temporary Notochordal tube and what happens to the tube? Where does it float?

Notochord cells fill in the tub

It detaches from the endoderm and floats between the ectoderm and endoderm

What tissue surrounds the definitive notochord?

Mesoderm

Proteoglycans are made of what glucosaminoglycans?

Chondroitin sulfate

Keratin sulfate

At what age do Notochordal cells start to degenerate?

Age 10

Are the chondrocyte cells of the nucleus pulposus antigenic?

Yes - create inflammation if they contact immune system

What grade of annular tear will start causing pain?

Grade 3

What might occur if a large chunk of the notochord does not degenerate?

Chordoma -cancerous tumor

Chordomas account for what percent of malignant bone tumors?

2%

By the end of what week has the primitive streak almost completely cleared out?

Wk 4

What end of the primitive streak does not degenerate?

Caudal end

What structure do the caudally clumped primitive streak cells from?

Tail bud

What does the tail bud form?

Most caudal region of the neural tube

Sacral and coccygeal spinal cord levels

Sacral and coccygeal Vertebral levels

What is diastematomyelia?

Split cord malformation - person has two spinal cords

What causes diastematomyelia?

Failure of the neurenteric canal to close

How many segments does diastematomyelia run?

2 to 3 segments

Where does diastematomyelia most commonly form?

Lower thoracic spine

What is the problem with the two spinal cords of diastematomyelia?

They get tethered to the septum causing mechanical irritation

What are frequent comorbidities associated with diastematomyelia?

Congenital scoliosis -70% of the time

Lumbosacral radiculopathy

What is secondary neurulation?

Process of building the sacral and coccygeal part of the neural tube from the tail bud

What does the sacrococcygeal portion of the neural tube derive from?

Primitive streak- specifically tail bud cells

What does the tail bud give rise to?

Sacral and coccygeal somites and sacral neural crest cells

What is neurulation?

Formation of CNS - brain and spinal cord

What germ layer does neural tissue derive from?

Ectoderm

What week does neurulation start?

Wk 3

What are the four stages of neurulation?

1) formation of neural plate

2) elongating and shaping neural plate

3) lateral folding of plate

4) rolling up and escape

What structures induce ectoderm cells of the cranial midline to differentiate into a new cell type?

Primitive node - main

Notochord - main

Prechordal plate

Anterior visceral endoderm (AVE)

What cell type do ectodermal cells turn into when BMP-4 is turned off ?

Neuroectoderm cells

What cells make up the neural plate?

Neuroectoderm cells

What does bone morphogenetic protein 4 do? (BMP-4)

When it’s turned off ectoderm cells morph into neural tissue

What two inhibitors of BMP4 does the primitive node secrete?

Noggin

Chord in

What inhibitor does the notochord, AVE, and prechordal plate cells secrete for Neuroectoderm formation?

Cerberus -1

What is the process of converting epithelial type tissue to neural tissue called?

Neural induction

What is neural induction?

Conversion of epithelial tissue to neural tissue

What structure does the brain derive from?

Neural plate

What structures does the neural plate develop between?

Primitive node and oropharyngeal membrane

Ectoderm and endoderm

What structure does the neural tube derive from?

Neural plate

What is step 2 of neurulation?

Elongating the neural plate to make the spinal cord

What portion of the neural plate to cells begin to mitose for elongation?

Caudal region

What direction does elongation of the cranial neural plate form?

Cranial to caudal