B5.069 Development of the GI System Flashcards
when does this endoderm epithelium dramatically change shape?
day 20-26
components of endodermal epithelium at day 26
foregut midgut hindgut allantois vitelline duct yolk sac
only organ suspended by 2 mesenteries
stomach
dorsal and ventral mesenteries
stomach rotation
rotates 90 degrees clockwise, left vagus ends up anterior and right vagus posterior
original posterior portion grows larger forming the greater curvature
what do the mesenteries develop into?
dorsal = greater omentum ventral = lesser omentum
prevalence of pyloric stenosis
2 in 1000 births
2nd most common GI abnormality after Meckel’s
typically in males (4x more likely)
first 2-6 weeks of life
symptoms of pyloric stenosis
severe projectile non-bilious vomiting
dehydration and weight loss
hypochloremia due to loss of gastric acid in vomit
cause of pyloric stenosis
hypertrophy of pyloric sphincter muscles to the point of pyloric stenosis
no gastric contents can enter first portion of duodenum
can sometimes palpate “olive” in anterior abdominal wall caudal to xyphoid process
what organs are derives from foregut endoderm
(lungs)
liver
gallbladder
pancreas
what structure forms the diaphragm
septum transversum
what is the bare area of the liver
liver fuses with developing diaphragm resulting in bare area surrounded by coronary ligament
discuss the origin of the falciform ligament and lesser omentum
liver growth causes lower portion of the septum transversum to thin, leaving the falciform ligament anterior and lesser omentum posterior to the liver
where do pancreatic buds originate
dorsal and ventral buds form on opposite sides of the gut tube
during the 5th week smaller ventral pancreas migrates around and fusion forms definitive pancreas
what happens if dorsal and ventral pancreatic buds don’t fuse?
typically don’t cause problems until sometimes in adult lift
major pancreatic duct
Wirsung
more caudal
always present
accessory pancreatic duct
Santorini
superior if present
annular pancreas
thought to arise when two (bilobed) ventral pancreatic buds form and migrate in opposite directions constricting the duodenum
severity of annular pancreas
some only partly block lumen
typically obstruct bile flow and pancreatic juice flow into lumen
classification of annular pancreas
classified into 6 subtypes based upon the drainage site of the annular duct
prevalence of annular pancreas
rare, 1 in 15,000 newborns
symptoms of annular pancreas in newborns
may have complete blockage of duodenum leading to polyhydramnios
present with difficulty feeding after birth
non-bilious vomiting and nausea
abdominal distention
other pathologies associated with annular pancreas
maternal polyhydramnios Down syndrome esophageal and duodenal atresias imperforate anus Meckel's diverticulum
what is duodenal atresia
congenital duodenal obstruction
presentation of duodenal atresia
early (within 24 hrs) with vomiting that may or may not contain bile, depending on atresia location
abdomen is not dilated bc distal intestines have not fully developed
duodenal atresia imaging findings
gas in stomach and 1st portion of duodenum, but not more distally (double bubble)
CT rules out annular pancreas and other associated congenital defects
prevalence of duodenal atresia
1 in 10,000 births
8% of downs syndrome infants
other pathologies associated with duodenal atresia
polyhydramnios in 50%
VACTERL in 50%
VACTERL
vertebral abnormalities anal atresia cardiac defects trachea-esophageal fistula renal anomalies limb abnormalities
discuss gut tube occlusion
6th-9th week
gut tube goes from hollow to occlusion of the lumen by endodermal cell proliferation
1-2 weeks later recanalized and hollow again
recanalization error possibilities
- cysts
- duplications
- septa
- diverticuli
- failure to reopen lumen
true vs false diverticulum
true contains all layers of wall, false only has outpunching of certain layers
most common locations of GI duplications
ileum and thorax
what is a GI duplication
developmental duplication of a segment of the GI tract
may occur anywhere along the tract, though certain sites are more common
may be cystic or tubular
on mesenteric side of bowel
share common wall but do not communicate with intestine
midgut organs
primary intestinal loop
SMA axis
formation of primary intestinal loop
rapid growth and elongation in 5th week
vitelline duct connects loop to yolk sac
90 degree rotation
physiological herniation of the midgut
6th week to 10th week
intestines physiologically herniate out of the embryo
same time during filling and recanalization
return of the intestine to the peritoneal cavity
end of 10th week
another 180 degree rotation, large intestines now “frame” small intestines”
vitelline duct lost around this time
omphalocele
failure of gut to return to the peritoneal cavity
loops covered with the amnion which is attached to an enlarged umbilical cord
prevalence of omphalocele
1 in 5,386 in US
small- SI only
large- can involve liver and spleen
detection of omphalocele
often detected by prenatal ultrasound or as a consequence of elevated AFP levels
when is AFP tests in pregnant women
14th-22nd week
most accurate 16-18th weeks
association of omphalocele with other pathologies
25-40% heart defects neural tube defects diaphragmatic hernia chromosomal abnormalities, nearly half have trisomy
treatment of omphalocele
saran wrap over exposed intestines until surgery
organs returned to cavity with time and growth
umbilicus surgically closed
risk factors for omphalocele
alcohol and tobacco
SSRIs
obesity
when is international omphalocele awareness day
jan 31
so just be aware of that
gastroschisis
failure of body wall closure followed by gut herniation
failure of the anterior body wall typically occurs to the right of the umbilicus
herniate intestines are NOT covered with a membrane
prevalence of gastroschisis
1 in 10,000
more frequent in young teenage mothers
detection of gastroschisis
prenatal ultrasound
elevated AFP
as early as 14 weeks
association of gastroschisis with other pathologies
NOT associated with other defects
inherited autosomal recessive
risk factors for gastroschisis
young mothers
smoking
drug abuse
low birth weight
treatment of gastroschisis
delivery by C-section at 36 weeks
placing man made materials over exposed intestines to limit volvulus prior to surgical repair
success of surgery in gastroschisis
successful 90% of the time
small repaired 24 hrs after birth
larger may require more steps
what are gut rotation abnormalities
malrotation of the intestines
2 most common malrotations
- only initial 90 degrees of rotation occurred: small intestines to the right of large
- revere rotation of initial 90 degree rotation, duodenum falls in front of colon
volvulus
if normal rotation fails, there is spontaneous compromised blood supply to a section of the GI tract
result of volvulus
intestinal atresia
vascular accidents
most commonly atresias and stenosis
occur in 1 in 1500 births
most frequently in duodenum, least frequently in the colon
termination of the vitelline duct and allantois
programmed cell death (apoptosis) in 10th week
human umbilical cord at time of birth
2 umbilical arteries
1 umbilical vein
Wharton’s jelly protects vessels
congenital vitelline duct defects
occur if vitelline (omphalomesenteric) duct does not undergo apoptosis
vitelline ligament
vitelline cyst
vitelline fistula
Meckel’s diverticulum
remnant of where the vitelline duct was attached to the ileum
appearance of Meckel’s diverticulum
2 inches long
2 feet proximal to ileocecal junction
2 types of ectopic tissue: gastric and pancreatic
symptoms of Meckel’s
abdominal pain
blood in stool
prevalence of Meckels
2% of the population
< age 2
2x as frequent in boys than girls
what is Hirschsprung disease
failure of enteric neural crest cells to migrate around the developing intestines resulting in a non-motile portion of the bowel
lack of parasympathetic innervation
genetic component of Hirschsprung
failure of RET gene, tyrosine kinase receptor
prevalence of Hirschsprung
1 in 5,000
males 4x more frequent than females
9% in downs individuals
how is Hirschsprung identified
infants not dismissed until they have passed meconium
90% in first 24 hours
99% within 48 hours
Hirschsprung suspected after 48 hours
symptoms of Hirschspring
abdominal distention
constipation
diagnosis and treatment of Hirshsprung
barium enema or lower GI study showing non motile bowel section
generally must be removed surgically
what is the urorectal septum
grows down to separate hindgut from cloaca
creates one space for urine (bladder), and one for fecal matter (rectum)
what is imperforate anus
anal atresia
failure of anus to form or connect to the rectum
usually very obvious to detect
prevalence of imperforate anus
1 in 5000
part of VACTERL
associated with trisomy 18 and 21
treatment of imperforate anus
immediate surgical intervention which may involve a temporary colostomy
why are most screenings done between 14-20 weeks?
this is after most of the fetal GI development has occurred
