Embryology of the GI tract Flashcards
Regional specification of the gut tube into different components occurs as
lateral folding brings the 2 sides of the tube together
Specification in the gut tube is initiated by ______ that causes transcription factors to be expressed in different regions of the tube. It also requires interaction between the epithelium (endoderm) and mesenchyme (splanchnic mesoderm) initiated by ___
RA gradient (not that the gradient increases as you move down the tube). SHH
_____ specifies the esophagus
SOX2
_____ specifies the duodenum and pancreas
PDX1
_____ specifies small intestine
CDXC
______ specifies large intestine
CDXA
In addition to regionalization development of the gut tube also involves
- continuous elongation
- herniation past the body wall (into the umbilical cord)
- Rotation and folding for efficient packing
- Histiogenesis and further maturation of the epithelial lining
The gut tube becomes suspended by a ______ layered fold of peritoneum-dorsal mesentery
2-layered
the mesenteries are elections of ______ onto gut tube
parietal peritoneum
components of the foregut
- Esophagus
- Stomach and 1/2 duodenum
- Liver
- Gallbladder
- Pancreas
- Spleen
Components of the midgut
- 1/2 of duodenum
- jejunum
- Ileum
- Cecum and appendix
- Ascending colon
- 2/3 transverse colon
Components of the hindgut
- 1/3 transverse colon
- descending colon
- sigmoid colon
- rectum
- upper part anal canal
Foregut derivatives are supplied by branches of the _____
celiac artery
Midgut derivatives are supplied by branches of the
superior mesenteric artery
Hindgut derivatives are supplied by branches of the
inferior mesenteric artery
Sympathetics innervation: Preganglionic cell bodies for foregut
T5-T9
Sympathetics innervation: Preganglionic cell bodies for Midgut
T9-L2
Sympathetics innervation: Preganglionic cell bodies for Hindgut
T12-L2
Splanchnic nerve of foregut
Greater splanchnic nerve
Splanchnic nerve of Midgut
Lesser splanchnic nerve
Splanchnic nerve of Hindgut
Least splanchnic nerve
Preaortic ganglion for Foregut
Celiac
Preaortic ganglion for midgut
Superior mesenteric
Postganglionic axons of the foregut follow
Celiac artery
Postganglionic axons of the midgut follow
Superior mesenteric artery
Innervation of the hindgut is the least splanchnic nerve to the _____ and the lumbar splanchnics form L1 and L2 to the ______
aorticorenal plexus, inferior mesenteric plexus
Parasympathetics for the foregut and midgut have preganglionic cell bodies in the
brainstem
Parasympathetics for the hindgut have preganglionic cell bodies in
S2-S4
What is the nerve of the parasympathetics of the foregut and midgut
Vagus nerve (CN X)
What is the nerve for parasympathetics of the hindgut
Pelvic splanchnic nerves
What is the location of parasympathetic ganglia of the foregut and midgut
Organ walls
What is the location of parasympathetic ganglia of the hindgut
Organ walls
At the allantois becomes the
urachus (median umbilical ligament)
narrowed or occluded esophagus (esophageal stenosis or atresia) may be due to the incomplete ______, usually found in the lower 1/3
recanalization (in week 5 you have a open tube in week 6 it overgrows with epithelial tissue and you have apoptosis foreign the tube again)
Successful esophageal anastomoses may be performed in those few with “long gap” esophageal atresia greater than ___between the proximal and distal esophageal remnants using various lengthening techniques
3cm
what is colon interposition
a section of colon is taken from its normal position in the gut and transposed, with its blood supply intact, into the chest, where it is joined to the esophagus above and the stomach below.
What is gastric tube esophagoplasty
- A longitudinal segment is taken form the stomach, which is then swung up into the chest and joined to the esophagus
Gastric transposition
the whole stomach is freed, mobilized and moved into the chest attached to the upper end of the esophagus
what is zenke’s diverticulum
esophageal diverticulum posterior to the top half of the esophagus
what is barrettes esophagus
acid backing up from the stomach changes esophagus lining
The ____ surface of the stomach grows relatively faster than the _____ surface
dorsal, ventral
The abdominal esophagus and stomach start as a straight tube suspended by dorsal and ventral mesentery. The dorsal side of the tube grows rapidly, expands and there is a simultaneous _______ rotation of ____ degrees
Clockwise, 90 degrees
After the clockwise 90 degree rotation of the stomach the left side of the stomach now lies anterior and the right side posterior. Therefore, the left vagus becomes the _____ vagus and the right vagus becomes the _____ vagal trunk
Anterior, posterior
Hypertrophic pyloric stenosis usually presents ____ weeks after birth. And are the characteristics of the emesis
2-3 weeks. Projectile emesis with no bile
Duodenal atresia has a _____ sign
double bubble sign (gas distended stomach and proximal duodenum with no distal gas.)
What is a duplication cyst
is a tubular structure with an internal lining of gastrointestinal epithelium, smooth muscle in its wall and adherence to some portion of the alimentary tract
The liver, gallbladder, and bile ducts develop in the ____ mesentery
ventral
Does the pancreas start as two and then fuse together
Yes
______ coalesce around extra embryonic veins to form sinusoids
Hepatic cords (cells)
____ and _____ are outgrowths of the bile duct
Gallbladder and cystic duct
Growth of liver divides ventral mesentery into _____ and ______
Falciform ligament and lesser omentum
The ________ is the fibrous remnant of the ductus venous.
ligamentum venosum
________ is the obliterated left umbilical vein
Ligamentum teres hepatis
Extrahepatic biliary atresia
- incomplete canalization of the bile duct
- 1/15,000 live births
- Jaundice- high levels of bilirubin in bloodstream
- Dark urine- bilirubin filtered by kidney and excreted in urine
- Pale stool- no bile or bilirubin is being emptied into the intestine
- Tx- surgical correction or transplant
______ gene development of pancreas and duodenum
PDX1
Paired _____ genes specify endocrine cell lineages
homeobox
_____ gene produces cells secreting insulin, somatostatin and pancreatic polypeptide
PAX4
____ gene produces cells that secrete glucagon
PAX6
Islets of Langerhans appear in ____ fetal month
3rd
Insulin is secreted by the ____ month of fetal development
5th
The biliary system (gallbladder and cystic duct) initially develops as a tubular structure (pars cystica) arising from
elongation and molding of the caudal portion of the hepatic diverticulum
The dorsal and ventral pancreas fuse after
clockwise rotation of the ventral bud around the caudal part of the foregut
The pancreas is predominantly drained through the ______ , which joins the common bile duct at the level of the major papilla. The _______ empties into the common bile duct at the level of the minor papilla. The ________ comprises the duct shared between liver and the ventral pancreas. The main pancreatic duct derives form the merger of the dorsal and ventral pancreatic ducts
Vental pancreatic duct. Dorsal pancreatic duct. Hepato-pancreatic common duct
Annular pancreas
- Vental and dorsal pancreatic buds form a ring around the duodenum
- Presents as duodenal obstruction
Accessory or ectopic pancreatic tissue can be found
- form distal esophagus through the primary intestinal loop (roughly distal part of transverse colon)
- Most common in stomach or ileum (ileal or Meckel’s diverticulum)
What are the derivatives of the midgut
- Duodenum distal to entrance of bile duct
- Free small intestine (jejunum, ileum)
- Cecum and appendix
- ascending colon
- right (proximal) 2/3 of transverse colon
- superior mesenteric artery
Gut atresia and stenosis caudal to the duodenum are probably due to
vascular compromise
Gut atresia and stenosis in the upper duodenum is usually due to failure to
recanalize
Rapid growth of the midgut starts at about
6 weeks
Rotation and Fixation of the Midgut produces a
normal physiologic herniation. gut loops into the umbilical cord and as this happens, the loop rotates 90 degrees counterclockwise around the superior mesenteric artery. This occurs at about 6 weeks
The cranial end of the primary intestinal loop forms the ______. The caudal end forms the ____
distal duodenum to ileum, lower ileum to proximal 2/3 transverse colon
at about the ____ week, the herniated loop returns to the abdominal cavity and orated an additional _____ degrees
10th, 180 degrees (note that this is 270 degrees in total)
What is malrotation
- Partial rotation of the intestines
- abnormally positioned viscera
- increased risk of entrapment of portions of the intestine
- Usually presents within first week as duodenal obstruction with bilious vomiting
- infants- recurrent abdominal pain, intestinal obstruction, malabsorption/diarrhea, peritonitis, septic shock, solid food intolerance, common bile duct obstruction, abdominal distention, and failure to thrive
Symptoms of malrotation in infants
- Usually presents within first week as duodenal obstruction with bilious vomiting
recurrent abdominal pain, intestinal obstruction, malabsorption/diarrhea, peritonitis, septic shock, solid food intolerance, common bile duct obstruction, abdominal distention, and failure to thrive
What is a volvulus
- abnormal twisting of the intestines causing obstruction
- compromises the intestine or the blood flow
Omphalocele
- Herniation of abdominal contents through enlarged umbilical ring
- this is normal if it is temporary
- The gut should return into the abdomen as the embryo grows
- 25/10,000
- Midgut loop fails to return to abdominal cavity
- pale, shiny sac protrudes from base of umbilical cord
- often involved with other abnormalities such as: cardiac, neural tube, and chromosomal
Gastroschisis
- Failure of anterior abdominal wall musculature to close during folding
- gut contents not surrounded by membrane
- 1-2/10,000 but frequency is increasing in young women
- 15-19 years, incidence increased from 4/10000 to 26/5/10000
- Not associated with chromosomal abnormalities or other malformations
- Survival rate is excellent
What is Meckel’s diverticulum
- Ileal diverticulum
- remnant of vitelline duct
- asymptomatic
- gastric or pancreatic tissue
- failure of vitelline duct to close
- rule of 2’s (2% prevalence, 2:1 female predominant, location 2 feet proximal to the ileocecal valve in humans, and half of those who are symptomatic are younger than 2 years of age
If there is a fistula present in the ideal diverticulum then there is
fecal discharge through the umbilicus
what forms the majority of the enteric nervous system
Neural crest cells
Hirschsprung’s disease
- congenital aganglionic megacolon, is a motor disorder of the colon that causes a functional intestinal obstruction
- both plexuses are affected
- it occurs in 1/5,000 infants with a male to female predominance of 4:1
- The pathogenesis of the disease is failure of migration of the neural crest cells that form the colonic ganglion cells
- Without parasympathetic innervation, the colon cannot relax or undergo peristalsis, resulting in a functional obstruction
- 70-80% of the time the defect is in the descending or sigmoid colon, 1-20% are in the transverse colon, 3% entire colon
- decreased occurrence in more proximal parts b/c these are associated with higher mortality rate and/or increased incidence of multiple congenital abnormalities
tx: surgical: pull-through surgery and involves removing the section of the colon that has no ganglia cells, then connecting the remaining healthy end of the colon to the rectum
Primary retroperitoneal means
- any organ that developed outside the abdominal cavity which never had a mesentery to begin with
Secondary retroperitoneal means
portion of the gut tube whose mesentery has fused with the lining peritoneum
Intraperitoneal means
organs with mesentery
Rotation of the gut tube causes
- will change the size of the two original peritoneal cavities
- will change the anatomical relationship of the organs to one another (no longer a straight tube)
- Will cause changes (loss) of some of the dorsal mesenteries
- Structures will be primarily or secondarily retroperitoneal
