embryology Flashcards
6th week significance
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
two limbs of the midgut loop
cranial limb –> forms small intestine
caudal limb –> forms cecum/large intestine
midgut rotation one
midgut rotates 90 degrees within umbilical cord
so now, cranial part is on the R and caudal part is on the L
10th week significance
midgut reduces and returns to abdominal cavity
midgut rotation 2
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.
omphalocele
persistence of abdominal herniation
therefore, issue during week 10 (when the hernia reduces)
contents: herniated bowel, peritoneum, AND amnion
umbilical hernia
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
gastroschisis
defect of median plane of abdominal wall and incomplete closing of the lateral folds (4th week of development)
viscera protrudes into the abdominal cavity
nonrotation
caudal limb returns first
therefore, small intestine lies to the R where the colon should be and colon is more central
generally asymptomatic
reversed rotation
clockwise rotation
duodenum lies anterior to the transverse colon and posterior to the superior mesenteric artery
superior mesenteric artery compresses transverse colon
subhepatic cecum and appendix
cecum adheres to the liver and doesn’t descend into the iliac fossa
result - difficulty in diagnosing appendicitis
mixed rotation and volvulus
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.
Meckels diverticulum
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)
urorectal septum
mesenchymal tissue that divides the cloaca into
1. ventral primitive urogenital sinus
2. dorsal primitive rectum
3. cranial part of anal canal
complications due to faulty urogenital septum
fistula connection urinary and anal tracts
pectinate line
junction where endoderm meets surface ectoderm
where the sphincters are
2 parts of the anal canal (above and below pectinate line)
above - forms from hindgut (endoderm/cloaca)
below-forms from proctodeum (surface ectoderm)
anal stenosis
narrowed anal canal
anus in normal place though
urorectal septum deviates dorsally very slightly causing a very narrow canal
imperforate anus
failure of the anal membrane to perforate
anal agenesis w/ perineal fistula
anal cavity ends blindly (atresia)
can cause:
-anoperineal fistula
-anovaginal fistula
-anourethral fistula
anorectal agenesis
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)
rectal atresia
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
Hirschprung disease (megacolon)
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
