Embryology

Question 1

Where does body cavity form from?

Answer 1

lateral plate mesoderm - divides into parietal (somatic) and visceral (splanchnic) mesoderm

Question 2

parietal mesoderm

Answer 2

forms parietal serous membranes

Question 3

visceral mesoderm forms?

Answer 3

visceral serous membranes and muscles/CT of guts

Question 4

body wall defects due to failure of ventral body wall fusion

Answer 4

viscera herniates through defect:

• ectopic cordis
• gastroschisis
• bladder/cloacal exstrophy
• Cantrell’s pentology

Question 5

dorsal mesentery

Answer 5

• suspends gut tube to posterior body wall
• extends from caudal foregut to hingut
• mesoesophagus, greater omentum, splenorenal lig, phrenicocolic/splenic lig, mesentery proper, mesoappendix, transverse mesocolon, sigmoid mesocolon

Question 6

ventral mesentery?

Answer 6

suspeds gut tube to anterior body wall - extends from foregut to proximal duodenum
- derivatives: lesser omentum (hepatogastric, hepatoduodenal ligmanets), falciform ligament, coronary and triangular ligament.

Question 7

primary retroperitoneal

Answer 7

kidneys, ureters, bladder

Question 8

secondary retroperitoneal

Answer 8

• initially entire gut tube has dorsal mesentary, but fusion occurs: duodenum, ascending/descending colon; pancreas

Question 9

peritonealized

Answer 9

stomach, spleen, Parts 1/4 of duodenum, jejunum, ileum, transverse and sigmoid colon

Question 10

septum transversum forms…

Answer 10

plate of mesoderm which separates thoracic and peritoneal cavity.

• forms bulk of diaphragm; muscle and central tendon of diaphragm
• does not completely separate thoracic and abdominal cavities; leaves openings on either side of foregut called “pericardioperitoneal canals”
• mesoderm forms in neck from cervical somites C3,4,5 = phrenic n.

Question 11

pleuropericardial/peritoneal membranes

Answer 11

• pleuripericardial separate pleural and pericardial cavities
• pleuroperitoneal: separate pleural and peritoneal cavities

Question 12

what four sources contribute to formation of diaphragm?

Answer 12

septum transversum: central tendon and muscle

- pleuroperitoneal membranes: central tendon

Question 13

how does diaphragm position change?

Answer 13

mesoderm forms from cervical somites 3-5
will descend into thorax by week 8
innervation: motor: phrenic, sensory: phrenic to central tendon; intercostal nn. to muscle

Question 14

Posterolateral defect

Answer 14

type of congenital diaph, hernia
cause: Failure of pleuroperitoneal membranes to form.

• lungs and heart are compressed; common cuase of pulmonary hypoplasia

Question 15

parasternal hernia

Answer 15

more common

cause: Small gap between sternal and costal portion of diaphragm.
- can cause strangulation of herniated gut

Question 16

eventration of diaphragm

Answer 16

cause: Lack of muscle differentiation within diaphragm - failure of myotome migration
- results in abdomina viscera balooning, compression of lungs, and hypoplasia.

Question 17

3 germ layers contribution to gut tube:

Answer 17

1. endoderm: epithelium and glands (inner lining)
2. mesoderm: connective tissue and smooth muscle
3. ectoderm: epithelium at ends of tube

Question 18

foregut

Answer 18

esophagus, stomach, parts 1/2 of duodenum; liver, gallbladder, pancreas, spleen.

• celiac artery

Question 19

midgut

Answer 19

3/4 of duodenum, small intestine, cecum, appendix, ascending colon, proximal 2/3 or transverse colon

• SMA

Question 20

hindgut

Answer 20

distal 1/3 of transverse colon, anal canal

IMA

Question 21

esophageal atresias/stenoses

Answer 21

Failure of gut to recanalize (can affect entire gut; most common in duodenum).

• endoderm proliferates and forms a plug, recanalizations normally occurs and the plug is reopened.
• can also be caused by malformation of tracheoesophageal septum
• stenosis: incomplete recanalizations
• atresia: no recanalization

Question 22

congenital hiatal hernia

Answer 22

Cause: Failure of esophagus to fully elongate.

- pulls stomach through diaphragm

Question 23

tracheoesophageal fistula

Answer 23

Cause: Deviation of tracheoesophageal septum

• results in blind ending esophagus

Question 24

rotation of stomach

Answer 24

• stomach rotates 90 clockwise around longitudinal axis: dorsal part (greater curvature)is on left, ventral part (lesser curvature) on right
• stomach also rotates around anterioposterior axis: pyloric part moves upward and to right; cardiac portion moves down and to left

Question 25

omental bursa

Answer 25

- when stomach rotates it stretches dorsal mesentery. the Omental bursa comes to lie inferior and posterior to stomach - during later development, the layers of the greater omentum fuse - results in formation of greater omentum

Question 26

pyloric stenosis

Answer 26

Cause: Pathological hypertrophy of pyloric sphincter. - results in occulsion of pyloric region; vomitting and no weight gain

Question 27

what does spleen form from?

Answer 27

- forms from mesenchymal cells within the two layers of dorsal mesogastrium - rotation of gut results in spleen being on left side of ab. cavity

Question 28

liver and gallbladder formation?

Answer 28

- hetpatic diverticulum: outgrowth from second portion of duodenum

Question 29

liver formation

Answer 29

endoderm gives rise to parenchyma; mesoderm gives rise to stroma functions as a hematopoietic organ during 2nd month bile formation begins week 12

Question 30

gallbladder and cystic duct formation

Answer 30

- forms from an evagination of bile duct. | - because of rotation of foregut, bile duct passes posterior to duodenum

Question 31

extrahepatic biliary atresia

Answer 31

- blockage of biliary duct due to lack of recanalization | - results in an underdeveloped liver

Question 32

formation of pancreas?

Answer 32

arises from endodermal outgrowths of duodenum (dorsal and ventral buds). rotation of duodenum causes fusion of buds. most of pancreas is derived from dorsal bud - ventral bud forms the head and uncinate process - main pancreatic duct derived from ventral pancreatic duct and distal dorsal pancreatic duct - accessory pancreatic duct derived from proximal part of dorsal pancreatic duct

Question 33

aberrant pancreatic tissue

Answer 33

Cause: Abnormal migration of pancreatic tissue. | can degrade surrounding tissue

Question 34

Annular Pancreas

Answer 34

- atresia of pancreas b/c of bifid ventral pancreatic bud; during rotation the bifid bud encircles the duodenum. - after fusion of the pancreas, the annular tissue can constrict the duodenum

Question 35

duodenal atresia/stenosis

Answer 35

Cause : Failure of gut to recanalize (can affect entire gut; most common in duodenum). - often affecting 3///4th portions - digested food and bile are forcible vomited = green colord - distended epigastrium b/c overfilled stomach - baby not swallowing amnionic fluid - thus mother often has polydramnios

Question 36

Duodenum development

Answer 36

foregut: parts 1/2. midgut parts 2/3. | - as stomach rotates, pulls duodenum superirorly and to right, resulting in a C-shaped duodenum

Question 37

white vs. green vomit?

Answer 37

white vomit: proximal to 2nd part of duodenum | green: distal to 2nd part of duodenum

Question 38

midgut development

Answer 38

physiological herniation week 6 midgut rotates 270 counterclockwise midgut retracts weeks 10-12 (jejunum enters first to lie on left side, cecum returns last to lie in RLQ)

Question 39

omphalocele

Answer 39

Cause : Midgut loop fails to retract into abdomen. - tissue protrudes through umbilicus and is covered by amniotic membrane - often part of more severe syndromes

Question 40

gastroschisis

Answer 40

Cause: Ventral body wall defect; gut herniates through weakness in abdominal wall. - typically lateral to umbilicus on right. - usually results from incomplete fusion of ventral body wall during folding - herniated bowe is NOT covered by amniotic membrane; bathed in amniotic fluid

Question 41

umbilical hernia

Answer 41

Cause: Weakness in skin of umbilicus - results when gut herniates into umbilical cord after returning to abdominal cavity - loops of bowel herniate through an impercetl closed umbilicus along midline - herniated tissue is covered by skin, subcutaneous tisue

Question 42

Ileal diverticulum

Answer 42

Cause: vitelline duct fails to regress 2% of pop, 2x more likely in males, 2 feet distal of ileum, 2 inches long, 2% become symptomatic - presents similar to appendicitis, but appendicitis is rare in toddlers

Question 43

Malrotation of gut

Answer 43

may result in volvulus and potential loss of blood sypply

Question 44

atresias/stenoses of midgut

Answer 44

cause: recanalization defect or ischemia

Question 45

retrocolic hernia

Answer 45

entrapment of small intestine behind colon - can be due to failure of ascending colon to become retroperitoneal, resulting in a long mesocolon which may allow abnormal movements and potentially volvulus of the colon

Question 46

hindgut development

Answer 46

- cloaca: distal most portion of gut tube; endoderm lined cavity which will contribute to formation of hindgut and urogenital system - urorectal septum divides cloaca into urogenital sinus and anorectal canal - Cloacal membrane ruptures during week 7 - pectinate line; marks division between ectoderm/endoderm

Question 47

hirschprung's disease (congenital megacolon)

Answer 47

Cause: failure of neural crest to migrate into gut (usually hindgut) - results in absence of parasympathetic ganglia, thus a portion of gut is paralyzed, and tremendous distension of colon occurs - fecal matter is blocked in the paralyzed portion

Question 48

fistulas and atresias of hindgut

Answer 48

Cause: malformation of urorectal septum - rectourethral and rectovaginal fistulas result from an anterior displacement of the hindgut. - rectoanal atresias result from loss of vascular suppply or failure of recanalizations

Question 49

imperforate anus

Answer 49

cause: failure of cloacal membrane to rupture | - blocked anus