embryonic foldinh

Question 1

What is responsible for left-right asymmetry?

Answer 1

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

Question 2

what defect can occur + explain how?

Answer 2

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

Question 3

embryonic folding definition

Answer 3

converting the flat trilaminar disc into a more cylindric embryo due to longitudinal and transverse folding that occurs as a result of embryonic growth

Question 4

why does the folding take place?

Answer 4

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

Question 5

Explain lateral-medial folding

Answer 5

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

Question 6

What will the somatopleuric mesoderm form?

Answer 6

line the body cavities and lies more dorsally before folding

Question 7

what will the splanchnopeuric mesoderm form?

Answer 7

membranous coverings of the organs

initially placed more ventral

Question 8

why is most of the folding in the outer rim?

Answer 8

the developing notochord, neural tube and somites stiffen the dorsal axis of the embryo

the notochord cells have a high turgor pressure

Question 9

What does the lateral-medial folding form?

Answer 9

give rise to the ventral structures of the body

results in the amnion surrounding the embryo

Question 10

explain rostral folding

Answer 10

moves rostral structures ventrally

ventral movement of septum transversum

buccopharyngeal membrane

cariogenic region

primitive pericardial cavity

Question 11

explain caudal folding

Answer 11

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

Question 12

what does the endodermal gut tube form?

Answer 12

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

Question 13

how is the gut tube suspended ?

Answer 13

suspended from the dorsal body wall by the dorsal mesentery

Question 14

congenital defects in ventral body wall

Answer 14

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

Question 15

what is the amnion continuous with?

Answer 15

the embryonic ectoderm

Question 16

how is the umbilical cord formed?

Answer 16

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

Question 17

what signifies the end point of folding?

Answer 17

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

Question 18

what appears at day 22?

Answer 18

septum transversum

Question 19

what is the septum transversum?

Answer 19

a bar of mesoderm lying rostral to the cariogenic region

Question 20

what happens to the septum transversum during folding?

Answer 20

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

Question 21

what does the septum transversum go on to form?

Answer 21

separates the developing thorax and abdomen

main part of diaphragm

Question 22

what is the intraembryonic coelom initially divided into?

Answer 22

the pericardial cavity- thoracic and the peritoneal cavity- abdomen

Question 23

how is the pleural cavity formed?

Answer 23

outgrowth of the pleuropericadial folds of the body wall, forms a pericardial cavity ventral to the pleural cavities

Question 24

formation of the pericardium

Answer 24

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

Question 25

what does the septum transversum form specifically in the diaphragm?

Answer 25

amuscular central tendon

Question 26

congenital defect linked to pleuroperitoneal cavities

Answer 26

congenital diaphragmatic hernias- failure to lose the pleuroperitoneal canals

Question 27

why does the gut tube form different structures?

Answer 27

different signalling from splanchnic mesoderm results in endoderm epithelium responding different

due to HOX genes