Body Foldings and Cavities

Question 1

Intraembryonic coelom

Answer 1

Divides the lateral mesoderm into:
Somatic (parietal) layer of lateral mesoderm- continuous w/extraembryonic mesoderm covering amnion
vesicle

Question 2

Somatopleure

Answer 2

Somatic mesoderm and overlying embryonic ectoderm form body wall

Question 3

Splanchnopleure

Answer 3

Splanchnic mesoderm and underlying embryonic endoderm form embryonic gut

Question 4

Folding occurs where

Answer 4

In the cranial and caudal ends, and sides occur simultaneously
Embryo increases in length, but lateral edges cannot keep pace

Question 5

Head fold

Answer 5

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)

Question 6

Changes after folding

Answer 6

Pericardial cavity is ventral

Intraembryonic and extraembryonic coeloms are in communication

Question 7

Tail folding

Answer 7

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

Question 8

Lateral folds

Answer 8

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

Question 9

Gastrochisis

Answer 9

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

Question 10

Congenital epigastric hernia

Answer 10

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

Question 11

Parietal wall of body cavity is derived from

Answer 11

Somatic mesoderm

Question 12

Visceral wall of body cavity derived from

Answer 12

Splanchnic mesoderm

Question 13

Pericardial cavity

Answer 13

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

Question 14

Dorsal mesent3ry

Answer 14

Suspends foregut, midgut and hindgut in the peritoneal cavity

Question 15

Septum transversum

Answer 15

Expands and fuses with dorsal mesentery of the esophagus and pleuroperitoneal membranes to form primordium of the central tendon of the diaphragm

Question 16

Pleuropericardial folds

Answer 16

Pleuropericardial folds are cranial
Membranes fuse with mesenchyme ventral to esophagus at 7 weeks
Separate pericardial cavity and pleural cavities

Question 17

Pleurocardioperitoneal canals

Answer 17

Formed from bronchial buds
Splits mesenchyme into:
Outer layer- thoracic wall
Inner layer: fibrous pericardium

Question 18

Pleuroperitoneal folds

Answer 18

Pleuroperitoneal folds are caudal, located inferior to the lungs and separate pleural cavities from the peritoneal cavity

Question 19

Pleuroperitoneal membranes

Answer 19

Fuse with dorsal mesentery of the esophagus and septum transversum to form primordial diaphragm

Question 20

Dorsal mesentery

Answer 20

Median portion of diaphragm

Question 21

Myoblasts

Answer 21

Grow into the dorsal mesentery to form crura of the diaphragm

Question 22

How does phrenic nerve get to final destination

Answer 22

Myoblasts pull ventral rami (C3-C5) with them, passing through pleuropericardial membranes, and will subsequently lie on the fibrous pericardium

Question 23

Congenital diaphragmatic hernia

Answer 23

Viscera bulge into pleural cavity
Lung maturation may be delayed; polyhydramnios may be present
Left side typically impacted
Can be corrected at birth

Question 24

Failure of pleuroperitoneal folds to fuse to septum transversum can result in

Answer 24

Hernia of gut into the thorax