in the folding of the embryo, what three fold that happen at the sam time?
head, tail and transverse
Before any folding occurs, what structure is most rostral?
septum transversum –> gives rise to Diaphragm
Around what week does folding occur?
4th week
As the neural tube moves forward, what begins to close?
rostral neuropore
The notochord gets tucked ventrally and caudally, what now is the most rostral structure? most caudal?
from rostral - caudal:
intra-embryonic coelum –> heart tubes –> septum transversum
Before folding, what three things sit in the prochordal mesoderm?
1) Septum transversum
2) Heart tube
3) Intra-embryonic coelum
the membrane connecting the notochord with the prochordal mesoderm is?
oropharyngeal membrane
What is the purpose of the oropharyngeal membrane?
acts as a “hinge” or pivot point and all structures will rotate around each other
During this process a portion of yolk sac becomes engulfed as well and forms the?
foregut
the remainder of the yolk sac that is not engulfed during folding goes?
it is squeezed out the ventral midline
as the neural tube folds caudally, what moves?
the collecting stalk and alianois get shifted ventrally
after the head fold, where is the oropharyngeal membrane located?
ventral to all structures ( heart tubes, IEC and septum transversum)
what makes up the amniotic membrane?
EEM+Ectoderm
What are the clinical significances of the head fold?
1) foregut formed
2) oropharyngeal membrane ventral toCNS
3) heart is ventral to CNS and gut
4) heart is dorsal to intraembryonic coelom
5) septum transversum is caudal to heart
6) rostral neuropore closes
7) ectoderm now covers rostral end of embryo while amniotic cavity surrounds the rostral end of embryo
What are rostral neural tube defects?
anencephaly and exencephaly
during the tail fold, the portion of the yolk sac that gets engulfed forms the?
hind gut
the membrane connecting the notochord/neural tube with EEM is?
cloacal membrane
the cloacal membrane will give rise to?
the anus
the caudal portion of the hindgut that sticks out is called?
cloaca
the cloaca will give rise to the?
rectum and urinary bladder
What covers the caudal end of the embryo?
ectoderm
What surrounds the caudal end of the embryo?
amniotic cavity
consequences and clinical significance of the tail fold?
spina bifida and spinal dermal sinus
spinal dermal sinus- the epidermal cells end up proliferating in dura matter of spinal cord
After the folds, EEM will complete surround the embryo except at one spot? where and what does it give rise to?
ventral to the midline
it will give rise to umbilical ring
Before transverse folding, Mesoderm that is anterior to the IEC is called?
Somatic mesoderm
Before transverse folding, Mesoderm that is posterior to IEC is called?
Splanchnic mesoderm
What occurs during the lateral or transverse fold?
the body wall folds down on both sides to enclose the embryoonic cut and IEC
The Somatic mesoderm swings down as ectoderm swings down and surrounds what structure?
mid gut
What is a somatopleure?
somatic mesoderm of lateral plate + ECTOderm
What is a spanchopleure?
splanchnic mesoderm of lateral plate + ENDOderm
when mesenchymal cells (mesoderm) encouter a fluid filled space (like IEC)
epithelium, but since it is made of mesenchymal cells= mesothelium
at the end of the transverse fold, the IEC surrounds what mesoderm?
splanchnic
somatic mesoderm will give rise to?
PARIETAL, lining of body cavities
splanchnic mesoderm will give rise to?
VISCERAL- outer layer of the organ
Two fused layers of mesothelium is called?
Mesentery
During the transverse fold, what is the IEC continuous with?
chronic cavity
as the embryo starts to grow, the amniotic will expand and fuse with ?
amnion + chorion = amniochorionic membrane
what is the umbilical ring?
where ectoderm meets amnion
where do the umbilical vessels form?
in collecting stalk
what vessels compose an umbilical cord?
2 arteries and 1 vein
what are the contents and layers of the umbilius
1) many layers of EEM = collecting stalk
2) Allantois (located inside stalk)
3) umbilical BVs
4) yolk stalk (has its own layer of EEM)
After transverse folding, what surrounds the yolk stalk?
IEC
ectoderm and amniotic cavity cover the ventral embryo except at the?
umbilical ring
definitive umbilicus has formed and is wrapped in?
amniotic membrane
the transverse folding process gives rise to what structure?
midgut
can the midgut still communicate outside the embryo?
yes, it connects with the residual yolk sac outside the embryo via yolk sac through vitelline duct
What is gastroschisis?
means “split gut” - failure in the transverse folding process, allows contents of body cavities to communicate and herniate outside the embryo