2. Body Folding & Body Cavities Flashcards
what are the 3 phases of embryonic development
growth - cell division & elaboration of cell products
morphogenesis - develop shape, size, etc based on gene expression & regulation
differentiation - cells organize in precise pattern of tissure & organ
what makes the intraembryonic coelom
small spaces in central mesoderm grow and combine to make a U-shape
what does the IE coelom divide
divides lateral mesoderm into -
- somatic layer (parietal) - continous w/ EE mesoderm covering amnion
- splanchnic layer (visceral) - continous w/ EE mesoderm covering umbilical vesicle
what is the somatopleure
somatic mesoderm & embryonic ectoderm
- form body wall
what is the splanchnopleure
splanchnic mesoderm & underlying endoderm
-form embryonic gut
What drives the formation of the fetal position?
Growth at different paces
Development of the brain occurs faster than others driving the folding into fetal position. Lateral edges lag behind
what are the steps of cranial folding
& what is the result
week 4 (22 days) embryo elongate cranially & caudally - neural tube & developing brain tissue grows into amniotic cavity
grow over the orophayngeal mem
- places mouth in correct direction
- moves septum transversum, primordial heart, & pericardial coelom)
- forms foregut- primordium of pharynx, esophagus & lower resp system
what happens to the IE coelom after cranial folding
IE coelom repositioned into “folded U” & IE & EE coeloms in communication (caudal peritoneal cavity positioned to where IE & EE are continous)
folded U = pericaridal cavity (anterior) & 2 pericardioperitoneal canals on either side of (dorsal) forgut
what are the steps of tail folding
& what are the results
- downgrowth of SC primordium into amniotic cavity
- overgrowth & fold over cloacal membrane–> becomes anus
- reposition: hindgut (endoderm)
- primitive streak lies caudal after folding
- terminal hindgut dilate –> make cloaca = rudiment urinary bladder/rectum
what are the steps of lateral folding
- somatopleure extend ventrally from each side meet at midline & fuse ==> cylindrical embryo
- splanchnic later enclose developing gut (now gut surrounded by splanchnic medosderm for visceral layer)
Rapid growth of what produces the left and right lateral folds?
spinal cord and somites
What is the midgut connected to and when does it separate?
yolk sac,
separates during the 5th week of development
What is gastroschisis?
extrusion of abdominal contents thru abd folds
not covered by peritoneum –> bowel exposed to amniotic fluid which is salty & corrosive (intrauterine consequence)
occurs to the right of the umbilical cord rather than midline
failure of lateral body fold to fuse when ant abd wall forms during 4th week
What is a congenital epigastric hernia?
MIDLINE bulge of abdominal wall btn xiphoid process and umbilicus
bowel NOT exposed to amniotic fluid bc it is covered by skin and subcutaneous tissues
pleuroperitonial folds didnt fuse with septum transversum
what cavities make up the IE coelom
pericardial cavity
pleural cavity
peritoneal cavity
what lines the cavities?
mesothelium
- somatic mesoderm - parietal
- splanchnic mesoderm - visceral
Where is the pericardial cavity & pericardioperitoneal canals located in relation to the septum transversum?
pericardial cavity: cranial to the septum transversum
pericardioperitoneal canals: dorsal to septum transversum
What suspends the foregut, midgut, and hindgut in the peritoneal cavity?
dorsal mesentary
-holds gut in place while folding and movement is going on
what is the septum transversum
primordium of the central tendon of the diaphragm
what do the pleuopericardial folds seperate?
How do they do this
heart from lungs
- start superior to developing lungs
- –> grow from lateral body wall and enlarge to make pleuropericardial membranes
- –> membrane fuse w/ mesenchyme ventral to esophagus (week 7)
- –> seperate pericardial cavity & pleural cavities
what do the pleuroperitoneal folds seperate?
how do they do this
seperate lungs from abd
- start inf to lungs
- enlarge and project into pericardioperitoneal canals
- –> form pleuoperitoneal membranes
- –> continue to form as the lungs develep and pleural cavity expands/invades the body wall
(attached dorsolaterally to abdominal wall)
what happens when the bronchial buds grow into the pericardioperitoneal canals?
split mesenchyme into:
outer layer (thoracic wall)
inner later (fibrous pericardium - outer later of pericardial sac)
explain the steps of how the pleuroperitoneal fold grows
- grows toward midline becomes pleuroperitoneal membrane
- fuses w/ dorsal mesentery of esophagus & septum transversum (week 6)
- seperate pleural cavities & peritoneal cavities
- myoblasts migrate into pleuroperitoneal mem & close the process (right closes a litte before left bc its smaller)
what 4 components contribute to the formation of the diaphragm & how
- septum transversum - fuse w/ dorsal mesentery of esophagus & pleuroperitoneal mem ==> central tendon of diaphragm
- pleuoperitoneal membranes - fuse with w/ dorsal mesentery of esophagus & septum transversum ==> primordial diaphragm
- dorsal mesentery ==> medial portion of diaphragm
- myoblasts - grow into the dorsal mesentery ==> crura of the diaphragm
What spinal level does the diaphragm begin during development?
C1-C3
How does the diaphragm receive phrenic nerve innervation?
myoblasts pull ventral rami of C3-C5 with them when moving –>
pass through pleuropericardial membranes –>
phrenic lies on the fibrous pericardium
What is a congenital diaphragmatic hernia?
- Failure of the pleuroperitoneal membrane to close the pericardioperiotoneal canal.
- Usually due to lack of/decreased myoblast infiltration.
- herniation of abdominal contents into the thorax.
- 80% on LEFT side.
- May delay lung development, lung hypoplasia.
- Polyhydramnios may be present
What is the omphaloenteric duct?
connection between the embryonic midgut and yolk sac. Walls are splanchnopleure
what are the results of lateral folding
- form abd wall - incorporate endoderm to make midgut
- connection btn umbilical vesicle & midgut reduced (form omphaloenteric duct)
- umbilical cord forms- connection btn IE & EE coelom narrow
- amnioitc cavity expands - obliterates most of EE coelom
