Body Cavities Flashcards
Which germ layer forms the neural plate? How is its differentiation induced?
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)
What is hindbrain and spinal cord induction depedent on?
FGFs and WNT3a
How does the neural tube form?
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)
List the process of neurulation:
Neural crest cells
Molecular regulation: BMPs, FGF, WNT, PAX2
Placode formation
Closure
Origin
Migratory pathways
List neural tube defects that can occur during neurulation:
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
What molecular regulators is the ectoderm involved with?
Noggin, chordin, follistatin, WNT, FGF and RA, and homeobox genes
List the derivatives of the paraxial mesoderm:
Somites, bones, connective tissue, muscles, dermis
scleretome, dermotomes, myotomes
Somitomeres form in head regions and contribute to the skull and muscles of the face
What molecular regulators are involved with the paraxial mesoderm?
Noggin and SHH
List the derivatives of the intermediate mesoderm:
The urogenital structures
List the derivatives of the lateral plate mesoderm:
Parietal or somatic mesoderm - lines body cavities
Splanchnic or visceral mesoderm - surrounds organs
What germ layer is blood and vasculature derived from?
The mesoderm
Describe the difference between vasculogenesis and angiogenesis:
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
What does mesenchyme refer to?
Any loose connective tissue regarless of origin
What are the derivatives of the endoderm?
The gut and gut derivatives
Liver, pancrease, lungs…etc.
Decscribe the process of initial folds during body cavity formation:
- Cephalocaudal folding (head and tail folds)
- 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
Decscribe the process of cranial-caudal closures during body cavity formation:
- 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
Primitive body cavity
Same as intraembryonic cavity (coelom)
What three cavities are derived from space between the two layers of the lateral plate mesoderm?
Cardiac, pleural, and peritoneal cavities
Splanchnic layer
Of caridac, pleural, and peritoneal cavities
Visceral - surrounds gut tube, heart and lungs
Somatic layer
Of caridac, pleural, and peritoneal cavities
Parietal - lines body walls
What occurs when body cavities fail to close?
Ectopia cordis, gastroschosis, and bladder and cloacal extrophy
Omphalacele - exception
What is the basic priniciples of body cavity formation during embryonic dedvelopment?
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
Septum transversum
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
Pericardioperitoneal canals
posterior to septum transversum - connect primitive pleuropericardial and peritoneal cavities
What closes the pericardioperitoneal canals?
The pleuropericardial membranes
What separates the pleural and pericardial cavities?
The pleuropericardial folds (membranes) grow around the heart and separate the pleural and pericardial cavities - form the fibrous pericardium
What molecular regulation is involved in the division of cavities?
Contain conserved DNA binding motif from the homeotic gene complex of drosophila
Grouped into four clusters
Regulate anterior-posterior (craniocaudal) patterning of the embryo
When is the period of organogensesis?
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.
Diaphragm (describe embryonic development)
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
When do the hypoblast cells fully dissapear?
During neural plate induction. The migrating epiblast cells during gastrulation displace the hypoblasts to form the endoderm.
When does neurulation take place?
Early in the third and through the fourth weeks of embryonic development.
Does gastrulation cease during neurulation?
No, gastrulation continues to develop from cranial to caudal.
When does neurulation end?
~28 days after fertizilation
When do the neural crest cells appear at the spinal cord area?
After the neural tube is closed
When do the neural crest cells appear at the crainial aspect?
Before the neural tube is closed
Crest cells account for ____ of birth defects:
1/3 or 33%
What is commonly sequelae to spina bifida?
Tethered cord and hdyrocephaly
Where is the paraxial mesoderm located and what does it differentiate into?
The paraxial mesoderm is proximal to the notocord and differentiates into somites.
Differentiates into vertebrae and most of the musculature
What does the lateral plate mesoderm form?
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.
When does the amniotic cavity formed?
Toward the end of neurulation
Where is the parietal and visceral mesoderm continuous at toward the end of neurulation?
The dorsal mesentery
Provides access for nerves and blood vessels to get to the gut (dorsal mesentery suspends gut tube)
What is the connection between the yolk sack and the gut tube?
The Vitelline duct (yolk-sack duct)
What are ventral body wall defects?
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
The right lateral fold grows at a different rate than left (95% are right sided)
What embryonic tissue is the septum transversum?
Mesoderm
The reason why the pericardial peritoneal canal forms
During cavity formation what segments the thoracic and peritoneal cavities?
The diaphragm
Where is the most common site of a diaphragmatic hernia?
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.
What creates the central tendon of the diaphragm?
The pleuroperitoneal membrane (these also signal muscles cells of the diaphragm to migrate)
What closes the pericardial-peritoneal canals?
The pleuroperitoneal membrane
When is the neural plate formed?
Week 3 (~20 days after fertilization)
What is the embryonic cell orgiin of the mandible?
Neural crest cells
What causes death in caudal agenesis/dysgenesis (sirenomelia)?
Gastrulation fails to form the kidneys
What embryonic tissue do the kidneys arise from?
The intermediate mesoderm
