Development of GI system Flashcards
outer tube of flat trilaminar disk
ectoderm, covers outer surface of embryo (except umbilical region)
central tube of flat trilaminar disk
endodermal primary gut tube
middle tube of flat trilaminar disk
mesoderm
contains coelom or body cavity
How does the midgut remain in communication with the yolk sac?
vitelline duct
what forms the epithelial lining of GI tract and parenchyma of derivative glands
endoderm
what forms the smooth muscular components of the GI tract
splanchnic (visceral) mesoderm
cranially, foregut terminates in
buccopharyngeal membrane
caudally, hindgut terminates in
cloacal membrane
at the buccopharyngeal and cloacal membranes –> what fuses?
endoderm fuses w/ ectoderm excluding the mesoderm
double-layered connection between splanchnic mesoderm and somatic mesoderm
dorsal mesentery
organ completely covered by peritoneum (having a mesentery) is called
intraperitoneal
organ covered by peritoneum, only on anterior surface
retroperitoneal
ventral mesentery
liver develops between this
pharyngeal gut (or pharynx)
from buccopharyngeal membrane –> respiratory diverticulum
respiratory diverticulum
out pouching of upper part of foregut, first rudiment of lung
tracheoesophogeal septum
separates upper part of foregut into ventral trachea and dorsal esophagus
upper 2/3 of trachea n. supply
vagus n.
striated muscle
lower third of esophagus n. supply
autonomic n.
smooth muscle
lung bud appears from ventral surface of foregut when?
4th week of devel
bronchial buds –>
R main bronchi –> forms 3 secondary bronchi
L main bronchi –> forms 2 secondary bronchi
pulmonary agenesis
lung bud fails to split into R and L bronchi and continue growing (bronchial morphogenesis)
result: abnormal number of lobes/bronchial segments, complete absence of lung, abnormal number of alveoli
possible CXR findings for pulmonary angenesis
complete opacity of R hemithorax
displacement of heart and mediastinum
tracheal displacement to R
esophageal atresia
congenital malformation
failure of esophagus to develop continuous passage into stomach
infants exhibit choking, coughing, aspiration pneumonia
trachea-esophageal fistula
trachea and esophagus fail to separate into distinct structures, passage created between them
infants exhibit choking, coughing, aspiration pneumonia, cant pass catheter thru esophagus to stomach
often assoc w. other anomalies like ventricular septal defect/patent ductus arteriosus/tetralogy of fallout
stomach at 4th/5th weeks
stomach is a dilatation of foregut, rotates 90 degrees clockwise, vagus n. follows rotation
stomach at 7th and 8th weeks
rotate santeroposteriorly
caudal (pyloric end) moves up and to R
cranial (cardiac end) moves down and to L
overal, axis of stomach runs from above L to below R
what forms lesser sac/omental bursa
dorsal mesogastrium being pulled to L, forming space behind stomach
two ligaments next to spleen in dorsal mesogastrium
lienorenal ligament (splenicorenal ligament) gastrolienal ligament (gastrosplenic ligament)
iliorenal ligament contains
splenic vessels
tail of pancreas
gastrolienal ligament contains
short gastric vessels
L gastroepiploic vessels
congenital hypertrophic pyloric stenosis
thickening of pylorus
narrowing of pyloric canal and obstruction to passage of food
stomach –> markedly distended, infants expel food w/ nonbilious projectile vomiting
progressive loss of fluid, H, Cl –> metabolic alkalosis and dehydration
bilious vomiting
obstruction distal to entrance of bile duct via ampulla of water (2nd pt of duodenum)
nonbilious vomiting
obstruction proximal to entrance of bile duct
duodenum develops from
caudal part of foregut and cranial end of midgut
Error in which part of duodenum development can lead to duodenal stenosis or atresia
5th/6th week, lumen of duodenum becomes smaller and temporary obliterated bc of proliferation of epithelial cells
If no recanalization –> stenosis/atresia
most duodenal atresia involve which parts of the duodenum?
which comorbidity these pts have 25% of time?
2nd/3rd part duodenum distal to opening of bile duct
results in bilious projectile vomiting
25% of cases have Down Syndrome
duodenal atresia
complete occlusion of duodenal lumen
in infants, vomiting begins a few hours after birth, almost always CONTAINS BILE
prenatal ultrasound shows double-bubble sign
can lead to polyhydramnios
double-bubble sign
prenatal ultrasound of pt w/ duodenal atresia
results from overfilled stomach and superior part of duodenum
polyhydramnios
xs amniotic fluid bc fluid cant pass to stomach and intestines for absorption and transfer thru placenta to mother’s blood for disposal
can be due to duodenal atresia or esophageal atresia
sx: dyspnea, edema, abd distension, preterm labor
oligohydramnios
deficiency of amniotic fluid
liver bud
aka hepatic diverticulum
appears day 22 from caudal end of foregut (midway thru 2nd pt of duodenum)
penetrates septum transverse and divides ventral mesentery
connection w/ duodenum narrows to form hepatic bile duct
outgrowth of ventral wall of bile duct –> cystic duct and gallbladder
hepatocytes are formed from which germ layer
endoderm
connective tissue of liver gallbladder is derived from which germ layer
splanchnic mesoderm
visceral peritoneum
hemopoietic cells
Kupffer cells (macrophages)
derived from?
mesoderm of septum transversum
serial membrane of septum transverse becomes _____, which covers most of the surface of the liver except _____
serial membrane of septum transverse becomes VISCERAL PERITONEUM, which covers most of the surface of the liver except BARE AREA OF LIVER
zone of reflection of visceral peritoneum becomes
coronary ligament
remnant of ventral mesentery connecting liver to anterior wall becomes
falciform ligament
liver divides ventral mesentery into 3 parts…
thin peritoneal lining
falciform ligament
lesser omentum
extra hepatic biliary atresia
blockage of bile from liver to gall bladder
rare
due to failure of ducts to recanalize or liver infection during fetal development
jaundice occurs soon after birth
ventral mesentery gives rise to
lesser omentum
falciform ligament
visceral peritoneum of liver
hepatogastric ligament
uncinate process
of pancreas
hook-like
superior mesenteric a. and v. pass over this
pancreas develops from 2 buds
dorsal bud of duodenum
ventral bud from origin of liver bud
pancreas becomes _________ _________ as its mesentery fuses w/ the posterior abd wall
secondarily retroperitoneal
annular pancreas
occurs when two lobes of ventral pancreas migrate around the duodenum in opposite directions to fuse w/ dorsal bud
infant sx: feeding intolerance, bilious vomiting, abd distension
adult sx: abd pain, nausea, vomiting, upper GI bleed (stomach ulceration), acute or chronic pancreatitis
cephalic limb of primary intestinal loop forms
rest of duodenum
jejunum
part of ileum
caudal limb of primary intestinal loop forms
rest of ileum cecum appendix ascending colon proximal 2/3 of transverse colon
Physiological umbilical herniation
physiological herniation of the primary intestinal loop into the umbilicus due to continued midgut elongation and pressure from abdominal organ growth
week 6
midgut rotation
week 6
herniated primary intestinal loop rotates 270 counterclockwise about its long axis while the jejunum and ileum form, creating jejunal-ileal loops
midgut retraction
week 10
intestinal loops retract into the abd with the jejunum entering first, and the cecum (with its new vermiform appendix) entering last
absent or incomplete secondary rotation of midgut can lead to
small intestine located on R side of abd cavity
reversed secondary rotation of midgut
net rotation is 90 clockwise
viscera in normal location, but duodenum ANTERIOR to transverse colon –> can compress/obstruct colon
subhepatic cecum/appendix
cecum initially lies below the liver then descends to the right iliac fossa
failure to descend –> sub hepatic cecum/appendix
how do ascending and descending colons become secondarily retroperitoneal
they are pushed against posterior body wall causing fusion of their mesentery with the parietal peritoneum
structures that were intraperitoneal that become secondarily retroperitoneal during development
duodenum
pancreas
ascending colon
descending colon
midgut volvulus
malrotation of gut causes narrowed mesenteric line of attachment of midgut
ligament of treitz in abnormal position (lower, to R of midline)
small intestine loops can twist (corkscrew sign)
dilatation of proximal duodenum
gut atresia and stenoses
commonly occur where?
as a result of what?
can occur anywhere along intestine
mostly duodenum
fewest in colon
caused by “vascular accidents” due to malrotation and volvulus
blood supply torsion is comprised, segment dies
Meckel’s diverticulum
persistent vitelline duct (or yolk stalk)
small outpouching of ileum connected to umbilicus by fibrous cord fistula, cyst
98% cases: asymptomatic
can mimic appendicitis
sx: painless rectal bleeding, intestinal obstruction, volvulus, intussusception (collapsing in on itself)
omphalocele
failure of umbilicus to close completely
hernial sac from epithelium of umbilical cord (peritoneum)
ectopia cordis
failure of abd wall closure more superiorly
most cases –> death shortly after birth (infection, hypoxemia, cardiac failure)
gastroschisis
abd wall does not involve umbilicus
incomplete closure of lateral folds during 4th week
GI system does not function properly
congenital umbilical hernia
protrusion of intestines through IMPERFECTLY CLOSED umbilicus
hernia covered by subcutaneous tissue/skin
defect through linea alba, protrudes during crying/straining/coughing
~15-20% infants affected
which part of pancreas is derived from ventral pancreatic bud?
part of head of pancreas and uncinate process
smooth m. of GI tract is derived from
lateral plate somatic mesoderm
rotation of primitive intestinal loop occurs in a _______ direction and amounts to approx _____ degrees
counterclockwise direction
270 degrees
