Body Foldings and Cavities Flashcards
Intraembryonic coelom
Divides the lateral mesoderm into:
Somatic (parietal) layer of lateral mesoderm- continuous w/extraembryonic mesoderm covering amnion
vesicle
Somatopleure
Somatic mesoderm and overlying embryonic ectoderm form body wall
Splanchnopleure
Splanchnic mesoderm and underlying embryonic endoderm form embryonic gut
Folding occurs where
In the cranial and caudal ends, and sides occur simultaneously
Embryo increases in length, but lateral edges cannot keep pace
Head fold
Embryo elongates cranially and caudally (4th week/day 22)
Neural folds project dorsally and overgrow oropharyngeal membrane
Overgrowth moves septum transversum, primordial heart, pericardial coelom, and oropharyngeal membrane to ventral surface
Part of the endoderm of the umbilical vessel is incorporated as the foregut (primordium of pharynx/esophagus and lower respiratory system)
Changes after folding
Pericardial cavity is ventral
Intraembryonic and extraembryonic coeloms are in communication
Tail folding
Folding of caudal end of embryo is due to growth of the distal neural tube
The tail region projects over the cloacal membrane (anus)
Part of endoderm will form hindgut (descending colon/rectum)
Terminal hindgut dilates to form cloaca (rudiment of urinary bladder/rectum)
Before folding, primitive streak lies cranial to cloacal membrane, after folding, it is caudal
Lateral folds
Rapid growth of SC and somites produces R/L lateral folds
Abdominal wall forms and incorporates endoderm to form midgut (small intestine primordium)
Connection b/w umbical vesicle and midgut is reduced, forming omphaloenteric duct
As umbilical cord forms, communication b/w intra/extra embryonic coelomic cavities narrows
Amniotic cavity expands, obliterates most of extraembryonic coelom
Gastrochisis
Protrusion of viscera; site of the abdominal defect is to the right of the umbilical cord rather than midline
Differs from an umbilical hernia in that bowel is uncovered and floating in the amniotic fluid
Congenital epigastric hernia
Midline bulge of abdominal wall located b/w xiphoid process and umbilicus
Bowel is not exposed to the amniotic fluid because it remains covered by skin and subq tissue
Parietal wall of body cavity is derived from
Somatic mesoderm
Visceral wall of body cavity derived from
Splanchnic mesoderm
Pericardial cavity
Relocated ventrally, anterior to the foregut and cranial to the septum transversum
Opens into pericardioperitoneal canals, located dorsal to the foregut
Caudal peritoneal cavity is positioned where IE and EE coeloms are continuous
Dorsal mesent3ry
Suspends foregut, midgut and hindgut in the peritoneal cavity
Septum transversum
Expands and fuses with dorsal mesentery of the esophagus and pleuroperitoneal membranes to form primordium of the central tendon of the diaphragm
Pleuropericardial folds
Pleuropericardial folds are cranial
Membranes fuse with mesenchyme ventral to esophagus at 7 weeks
Separate pericardial cavity and pleural cavities
Pleurocardioperitoneal canals
Formed from bronchial buds
Splits mesenchyme into:
Outer layer- thoracic wall
Inner layer: fibrous pericardium
Pleuroperitoneal folds
Pleuroperitoneal folds are caudal, located inferior to the lungs and separate pleural cavities from the peritoneal cavity
Pleuroperitoneal membranes
Fuse with dorsal mesentery of the esophagus and septum transversum to form primordial diaphragm
Dorsal mesentery
Median portion of diaphragm
Myoblasts
Grow into the dorsal mesentery to form crura of the diaphragm
How does phrenic nerve get to final destination
Myoblasts pull ventral rami (C3-C5) with them, passing through pleuropericardial membranes, and will subsequently lie on the fibrous pericardium
Congenital diaphragmatic hernia
Viscera bulge into pleural cavity
Lung maturation may be delayed; polyhydramnios may be present
Left side typically impacted
Can be corrected at birth
Failure of pleuroperitoneal folds to fuse to septum transversum can result in
Hernia of gut into the thorax
