embryology

Question 1

6th week significance

Answer 1

umbilical hernia - protrusion because the peritoneal cavity is small (reduces eventually)

cecum undergoes differential growth - appendix remains narrow but increases in length, enters the cecum on the medial side

Question 2

two limbs of the midgut loop

Answer 2

cranial limb –> forms small intestine
caudal limb –> forms cecum/large intestine

Question 3

midgut rotation one

Answer 3

midgut rotates 90 degrees within umbilical cord
so now, cranial part is on the R and caudal part is on the L

Question 4

10th week significance

Answer 4

midgut reduces and returns to abdominal cavity

Question 5

midgut rotation 2

Answer 5

rotates another 180 degrees (270 total) so its vertical again. cranial enters first and occupies central part of abdomen .

caudal part (large intestine) enters next and occupies the R side of the abdomen. cecum and appendix descend to RLQ.

Question 6

omphalocele

Answer 6

persistence of abdominal herniation
therefore, issue during week 10 (when the hernia reduces)

contents: herniated bowel, peritoneum, AND amnion

Question 7

umbilical hernia

Answer 7

protruding mass through umbilicus
covered in skin and subcutaneous tissue

midgut is reduced during week 10 but the umbilicus does not close properly

amnion NOT involved

Question 8

gastroschisis

Answer 8

defect of median plane of abdominal wall and incomplete closing of the lateral folds (4th week of development)

viscera protrudes into the abdominal cavity

Question 9

nonrotation

Answer 9

caudal limb returns first
therefore, small intestine lies to the R where the colon should be and colon is more central

generally asymptomatic

Question 10

reversed rotation

Answer 10

clockwise rotation

duodenum lies anterior to the transverse colon and posterior to the superior mesenteric artery

superior mesenteric artery compresses transverse colon

Question 11

subhepatic cecum and appendix

Answer 11

cecum adheres to the liver and doesn’t descend into the iliac fossa

result - difficulty in diagnosing appendicitis

Question 12

mixed rotation and volvulus

Answer 12

cecum lies inferior to the pylorus (high up) and is fixed to the posterior abdominal wall by peritoneal bands –> may cause duodenal obstruction/dilation

failure of final 90 deg.

Question 13

Meckels diverticulum

Answer 13

vitelline duct persists
located 2 feet within ileocecal valve
may contain GASTRIC or PANCREATIC tissue
therefore can become inflamed because gastric tissue is secreting acid

sx resemble appendicitis but closer to umbilicus, not so much RLQ

may form vitelline cyst or a umbilicoileal fistula (connecting ileum diverticulum and umbilicus)

Question 14

urorectal septum

Answer 14

mesenchymal tissue that divides the cloaca into
1. ventral primitive urogenital sinus
2. dorsal primitive rectum
3. cranial part of anal canal

Question 15

complications due to faulty urogenital septum

Answer 15

fistula connection urinary and anal tracts

Question 16

pectinate line

Answer 16

junction where endoderm meets surface ectoderm
where the sphincters are

Question 17

2 parts of the anal canal (above and below pectinate line)

Answer 17

above - forms from hindgut (endoderm/cloaca)
below-forms from proctodeum (surface ectoderm)

Question 18

anal stenosis

Answer 18

narrowed anal canal
anus in normal place though
urorectal septum deviates dorsally very slightly causing a very narrow canal

Question 19

imperforate anus

Answer 19

failure of the anal membrane to perforate

Question 20

anal agenesis w/ perineal fistula

Answer 20

anal cavity ends blindly (atresia)

can cause:
-anoperineal fistula
-anovaginal fistula
-anourethral fistula

Question 21

anorectal agenesis

Answer 21

most common anorectal anomoly
incomplete separation of the cloaca by the urorectal septum

result:
rectum may end blindly and there may be a fistula to bladder (rectovesical), vagina (rectovaginal), or urethra (rectourethral)

Question 22

rectal atresia

Answer 22

anal canal and rectum are present but no communication exists between them
may be connected by fibrous band or tissue

due to:
1. abnormal recanalization
2. defective blood supply

Question 23

Hirschprung disease (megacolon)

Answer 23

absence of autonomic ganglia in the myenteric plexus of the narrowed segment, segment above becomes dilated

failure of migration of neural crest cells during weeks 5-7

most common cause of intestinal obstruction in neonates