embryonic foldinh Flashcards
What is responsible for left-right asymmetry?
nodal cilia- cells of the node have prominent cilia which rotate and create flow.
the cilia are tilted so the flow is linear rather than a vortex, causing fluid to flow from one site to the other
what defect can occur + explain how?
situs inversus, where the organs are flipped
caused by a single point mutation in the dynein heavy chain 11, which results in defective nodal cilia
embryonic folding definition
converting the flat trilaminar disc into a more cylindric embryo due to longitudinal and transverse folding that occurs as a result of embryonic growth
why does the folding take place?
due to a disparity in growth between two areas
craniocaudal due to expansion of neural tube,
transverse because of vigorous growth of embryonic disc and amnion with little growth of yolk sac
Explain lateral-medial folding
forms the first cavity within the embryo- the intraembryonic coelom running along the length of the embryo
during folding, the lateral plate mesoderm will divide into two layers during folding: somatopleuric and splanchnopleuric mesoderm
results in the ventral movement of lateral plate mesoderm
gut tube forms from the endoderm, resulting in a change of shape of the yolk sac
amnion is filled with amniotic fluid and like a water field balloon it collapses around the embryo
What will the somatopleuric mesoderm form?
line the body cavities and lies more dorsally before folding
what will the splanchnopeuric mesoderm form?
membranous coverings of the organs
initially placed more ventral
why is most of the folding in the outer rim?
the developing notochord, neural tube and somites stiffen the dorsal axis of the embryo
the notochord cells have a high turgor pressure
What does the lateral-medial folding form?
give rise to the ventral structures of the body
results in the amnion surrounding the embryo
explain rostral folding
moves rostral structures ventrally
ventral movement of septum transversum
buccopharyngeal membrane
cariogenic region
primitive pericardial cavity
explain caudal folding
caused primarily by growth of the developing spinal cord
cloacal membrane and the allantois (later forms part of the bladder) move ventrally
leads to formation of the hindgut tube
what does the endodermal gut tube form?
the yolk sac begins to look like a goldfish bowl, but as the gut tube forms the neck narrows to form the vitelline duct
rostral end of tube forms the foregut and the caudal ends the hind gut
these end in buccopharyngeal and cloacal membranes
how is the gut tube suspended ?
suspended from the dorsal body wall by the dorsal mesentery
congenital defects in ventral body wall
lateral folding does not fuse, so the ventral body wall is incomplete
omphalocele- herniating organs are membrane covered
gastroschisis- herniating organs are not membrane covered
what is the amnion continuous with?
the embryonic ectoderm
how is the umbilical cord formed?
embryonic folding and the expansion of the amniotic cavity leads to the formation of the umbilical cord
chorionic cavity eventually filled by the expanding amniotic cavity
what signifies the end point of folding?
the heart is in the correct position
ventral body wall is complete
the gut is a tube with the yolk sac attached by the vitelline duct, with the two membranes on either end
central midgut still opens ventrally to yolk sac
what appears at day 22?
septum transversum
what is the septum transversum?
a bar of mesoderm lying rostral to the cariogenic region
what happens to the septum transversum during folding?
rostral folding carries it ventrally so it wedges between the cariogenic region and the neck the yolk sac
caudal translocation with elongation of phrenic nerve C3,4,5
what does the septum transversum go on to form?
separates the developing thorax and abdomen
main part of diaphragm
what is the intraembryonic coelom initially divided into?
the pericardial cavity- thoracic and the peritoneal cavity- abdomen
how is the pleural cavity formed?
outgrowth of the pleuropericadial folds of the body wall, forms a pericardial cavity ventral to the pleural cavities
formation of the pericardium
pleuropericardial folds grow and fuse medially, subdividing the primitive pericardial cavity into the definitive pericardial cavity and two pleural cavities
the roots of the pleuropericardial folds then migrate around to the anterior body wall, forming the definitive pericardium
what does the septum transversum form specifically in the diaphragm?
amuscular central tendon
congenital defect linked to pleuroperitoneal cavities
congenital diaphragmatic hernias- failure to lose the pleuroperitoneal canals
why does the gut tube form different structures?
different signalling from splanchnic mesoderm results in endoderm epithelium responding different
due to HOX genes
