Body Cavities

Question 1

Which germ layer forms the neural plate? How is its differentiation induced?

Answer 1

The ectoderm forms the neural plate, which is induced by upregulation of FGFs while the node, notocord, and prechordal mesoderm block BMP 4 activity. -> This combination of increased FGFs and decreased BMP4 activates a neural pathway (fore and midbrain regions only)

Question 2

What is hindbrain and spinal cord induction depedent on?

Answer 2

FGFs and WNT3a

Question 3

How does the neural tube form?

Answer 3

The neural plate forms neural folds that elevate and fuse in the midline to form the neural tube = CNS. Crest cells are located at the top of the neural folds - neural crest- migrate to form bones and connective tissue.

The neural folds close in the middle (occipital) region of the plate (and “zipper” toward both ends, leaving the cranial region more open)

Question 4

List the process of neurulation:

Answer 4

Neural crest cells
Molecular regulation: BMPs, FGF, WNT, PAX2
Placode formation
Closure
Origin
Migratory pathways

Question 5

List neural tube defects that can occur during neurulation:

Answer 5

Spina bifida - open neural tube anywhere from cervical to lumbosacral (most common) - results from the neural folds failing to close.

Spina bifida occulta - neural tube closes but vertebra do not (covered by skin). Inherited disorder

Anecephaly - cranial neural folds fail to close causing brain tissue to degenerate (death results)

70% of all cases of spina bifida can be prevented by taking folic acid
Folic acid also works to prevent anencephaly

Question 6

What molecular regulators is the ectoderm involved with?

Answer 6

Noggin, chordin, follistatin, WNT, FGF and RA, and homeobox genes

Question 7

List the derivatives of the paraxial mesoderm:

Answer 7

Somites, bones, connective tissue, muscles, dermis
scleretome, dermotomes, myotomes

Somitomeres form in head regions and contribute to the skull and muscles of the face

Question 8

What molecular regulators are involved with the paraxial mesoderm?

Answer 8

Noggin and SHH

Question 9

List the derivatives of the intermediate mesoderm:

Answer 9

The urogenital structures

Question 10

List the derivatives of the lateral plate mesoderm:

Answer 10

Parietal or somatic mesoderm - lines body cavities
Splanchnic or visceral mesoderm - surrounds organs

Question 11

What germ layer is blood and vasculature derived from?

Answer 11

The mesoderm

Question 12

Describe the difference between vasculogenesis and angiogenesis:

Answer 12

Vasculogenesis - in situ- form blood islands first, then cells coalesce into endothelial tubes to establish major vessels - aorta and cardinal veins

Angiogenesis - new vessels sprout from existing vessels

VEGF and receptors involved in molecular regulation

Question 13

What does mesenchyme refer to?

Answer 13

Any loose connective tissue regarless of origin

Question 14

What are the derivatives of the endoderm?

Answer 14

The gut and gut derivatives

Liver, pancrease, lungs…etc.

Question 15

Decscribe the process of initial folds during body cavity formation:

Answer 15

1. Cephalocaudal folding (head and tail folds)
2. Lateral folds (one on each side) enclose the gut tube around the umbilical region to make the ventral body wall
   -create primitive body cavity
   -create gut tube
   -Vitelline duct (yolk sac duct) connects gut tube to yolk sac

Question 16

Decscribe the process of cranial-caudal closures during body cavity formation:

Answer 16

• Gut divided into pharyngeal, fore, mid, and hindgut
• Gut closed at cranial end-buccopharyngeal membrane
• Gut closed at caudal end - cloacal membrane
  -Cloaca - expanded portion of hind gut - later forms urogenital sinus and
  part of anal canal

Question 17

Primitive body cavity

Answer 17

Same as intraembryonic cavity (coelom)

Question 18

What three cavities are derived from space between the two layers of the lateral plate mesoderm?

Answer 18

Cardiac, pleural, and peritoneal cavities

Question 19

Splanchnic layer

Of caridac, pleural, and peritoneal cavities

Answer 19

Visceral - surrounds gut tube, heart and lungs

Question 20

Somatic layer

Of caridac, pleural, and peritoneal cavities

Answer 20

Parietal - lines body walls

Question 21

What occurs when body cavities fail to close?

Answer 21

Ectopia cordis, gastroschosis, and bladder and cloacal extrophy

Omphalacele - exception

Question 22

What is the basic priniciples of body cavity formation during embryonic dedvelopment?

Answer 22

Two sides of cavity are brought together by embryonic folding and overgrowth of the cranial region

Caudal and two lateral fold plus the overgrowth draws everything around the umbilical region

Two layers of lateral plate mesoderm form serous membranes that secrete fluid for lubrication

Two layers continuous at the root of each organ to form a mesentery

Gut is suspended by dorsal mesentery - double layer of peritoneum - where two layers are continuous

Question 23

Septum transversum

Answer 23

Block of mesetery derived from splanchnic mesoderm around the heart: moves to the region between the toracic and peritoneal cavities due to cranial folding that curved the heart into the thoracic region

Question 24

Pericardioperitoneal canals

Answer 24

posterior to septum transversum - connect primitive pleuropericardial and peritoneal cavities

Question 25

What closes the pericardioperitoneal canals?

Answer 25

The pleuropericardial membranes

Question 26

What separates the pleural and pericardial cavities?

Answer 26

The pleuropericardial folds (membranes) grow around the heart and separate the pleural and pericardial cavities - form the fibrous pericardium

Question 27

What molecular regulation is involved in the division of cavities?

Answer 27

Contain conserved DNA binding motif from the homeotic gene complex of drosophila Grouped into four clusters Regulate anterior-posterior (craniocaudal) patterning of the embryo

Question 28

When is the period of organogensesis?

Answer 28

The 3rd to 8th weeks - very sensitive to teratogenic insult because organ primordia are forming. Ebryo also sensitive in the first two weeks when craniocaudal and lef/right axes are forming.

Question 29

Diaphragm (describe embryonic development)

Answer 29

Pleuroperitoneal membranes: form the central tendon and provide scaffold for migrating muscle cells Muscular componenets - from cervical myotomes C3-5 - carry phrenic nerve with them Mesentery of the esophagus - crura Diaphragmatic hernia - usually on left - failure of muscle cells to reinforce plueroperitoneal membrane to close pericardioperitoneal canal; can also be caused by short esophagus - abdominal organs may compress lungs and heart

Question 30

When do the hypoblast cells fully dissapear?

Answer 30

During neural plate induction. The migrating epiblast cells during gastrulation displace the hypoblasts to form the endoderm.

Question 31

When does neurulation take place?

Answer 31

Early in the third and through the fourth weeks of embryonic development.

Question 32

Does gastrulation cease during neurulation?

Answer 32

No, gastrulation continues to develop from cranial to caudal.

Question 33

When does neurulation end?

Answer 33

~28 days after fertizilation

Question 34

When do the neural crest cells appear at the spinal cord area?

Answer 34

After the neural tube is closed

Question 35

When do the neural crest cells appear at the crainial aspect?

Answer 35

Before the neural tube is closed

Question 36

Crest cells account for ____ of birth defects:

Answer 36

1/3 or 33%

Question 37

What is commonly sequelae to spina bifida?

Answer 37

Tethered cord and hdyrocephaly

Question 38

Where is the paraxial mesoderm located and what does it differentiate into?

Answer 38

The paraxial mesoderm is proximal to the notocord and differentiates into somites. ## Footnote Differentiates into vertebrae and most of the musculature

Question 39

What does the lateral plate mesoderm form?

Answer 39

The lateral plate mesoderm that covers the amniotic cavity forms the parietal mesoderm layer. They lateral plate mesoderm that covers the yolk sack forms the visceral mesoderm layer.

Question 40

When does the amniotic cavity formed?

Answer 40

Toward the end of neurulation

Question 41

Where is the parietal and visceral mesoderm continuous at toward the end of neurulation?

Answer 41

The dorsal mesentery ## Footnote Provides access for nerves and blood vessels to get to the gut (dorsal mesentery suspends gut tube)

Question 42

What is the connection between the yolk sack and the gut tube?

Answer 42

The Vitelline duct (yolk-sack duct)

Question 43

What are ventral body wall defects?

Answer 43

Due to abnormal closure of one or more of the body folds: Ectopia cordis - heart outside of body Gastroschisis - gut outside Bladder and cloacal exstrophy - outside Midwall defects - Pectus excavatum or pectus carinatum ## Footnote The right lateral fold grows at a different rate than left (95% are right sided)

Question 44

What embryonic tissue is the septum transversum?

Answer 44

Mesoderm The reason why the pericardial peritoneal canal forms

Question 45

During cavity formation what segments the thoracic and peritoneal cavities?

Answer 45

The diaphragm

Question 46

Where is the most common site of a diaphragmatic hernia?

Answer 46

Left side - form because of failure of muscle cells to migrate of the pleuroperitoneal membranes (if large enough heart and intestines can migrate Shortening of the foregut can also cause this. Also, pleuroperitoneal folds not closing fully.

Question 47

What creates the central tendon of the diaphragm?

Answer 47

The pleuroperitoneal membrane (these also signal muscles cells of the diaphragm to migrate)

Question 48

What closes the pericardial-peritoneal canals?

Answer 48

The pleuroperitoneal membrane

Question 49

When is the neural plate formed?

Answer 49

Week 3 (~20 days after fertilization)

Question 50

What is the embryonic cell orgiin of the mandible?

Answer 50

Neural crest cells

Question 51

What causes death in caudal agenesis/dysgenesis (sirenomelia)?

Answer 51

Gastrulation fails to form the kidneys

Question 52

What embryonic tissue do the kidneys arise from?

Answer 52

The intermediate mesoderm