Development Of The GI Tract Flashcards
What are the three layers of trilaminar disc?
Ectoderm
Mesoderm
Endoderm
When does the embryonic disc form?
During 3rd week of development
What are the parts of mesoderm?
The paraxial mesoderm
The intermediate mesoderm
The lateral plate mesoderm
The interface between amniotic cavity and the yolk sac is the
Embryonic disc
Yolk sac forms
The digestive tube(tract)
Amniotic cavity folds in how many directions
4 directions
Embryonic disc is where
All the organs and structures in an adult come from
The endoderm forms
The lining (epithelium)of the GI tract,some accessory organs (many organs bud off :liver pancreas,trachea)and glands of the GI tract
Mesoderm forms
The stroma(GI tract connective tissue)and muscles surrounding abdominal structures in the GI tract,peritoneum and spleen
Foregut is supplied by
Celiac trunk
Midgut is supplied by:
Superior mesenteric artery
Hind gut is supplied by
Inferior mesenteric artery
When the foregut,midgut and hind gut forms, most of the yolk sac has disappeared except:
The vitelline duct(omphalomesenteric duct)
Portions of the GI tract includes
Forgut
Midgut
Hindgut
Foregut gives rise to everything supplied by the celiac trunk
All the structures from the mouth to ampulla of vater
Midgut gives rise to everthing supplied by SMA which includes;
Which includes structures from ampulla of vater to transverse colocn
Hindgut gives rise to structures supplied by IMA which includes
Transverse colon to rectum
Mesentery is
Double layer of peritoneum(sheets of connective tissue)
Function of mesentery
Suspends abdominal organs from cavity walls
Blood vessels also travel through the mesentery as they go from the aorta to the organs which they supply
Intraperitoneal organs
Enclosed by mesentery(within the peritoneal cavity)
Retroperitoneal organs
Covered by peritoniun only on anterior wall
Lie against the posterior abdominal wall
Mesentery comes from:
Mesoderm(mes in mesoderm mes in mesentery)
What are the two types of mesentery
Dorsal mesentery(towards the back of the fetus)
Ventral mesentery (towards the front of the fetus)
Most of the connective tissue structures comes from the:
Dorsal mesentery
The reason for this is because the gut moves away from the posterior wall in development and the dorsal mesentery grows between the gut and posterior wall so that most structures are covered by this mesentery
Ventral mesentery only exists in
Esophagus,stomach and
upper duodenum
Liver grows into this mesentery
In adult:lesser omentum and falciform ligament.
Ventral mesentery derives from
Septum transversum which is a mesenchyme tissue
Falciform ligament
Connects the liver to the anterior abdominal wall
Lesser omentum
Connects the liver and stomach(lesser curvature)
Mesentery goes by different names depending upon whcih abdomina organs it is surrounding
Mesentery around stomach:mesogastrium
Mesentery around the duodenum:mesoduodenum
Mesentery around the colon: mesocolon
Omentum is
Sheet of connective and fatty tissue.latin “apron”
Greater omentum
Hangs from greater curvature of stomach
Covers intestines
Formed from mesogastrium
Lesser omentum
Between stomach and liver
Formed from ventral mesentery
Lung buds off from
Esophagus(foregut)
Budding off of lung is called
Respiratory diverticulum ir lung bud
What divides the lung bud from the esophagus?
The tracheoesophageal septum
Abnormal development of tracheoesophageal septum results in:
Esophageal atresia(closed esophagus) this occurs when the septum deviates posteriorly cutting off the esophagus.
Name the types of esophageal atresia
1.Esophageal atresia with tracheoesophageal fistula(most common)which is connection between the trachea and the distal portion of the esophagus.the proximal portion has been cut off.
2.Pure esophageal atresia (less common)this is where proximal esophagus ends in blind tube and distal part is not connected to trachea at all.
3.H type (more rare)where esophagus and trachea are bith separate tubes but they are connected by a fistula.
What are the clinical features of esophageal atresia:
Esophagus does not connect to the stomach>baby can’t swallow fluid>polyhydromnios
Drooling choking and vomiting>due to accumulation of secretions which can’t be swallowed
NG is often passed into the stomach to control excess secretions but in the case of esophageal atresia Ng tube can’t be passed to the stomach as esophagus ends in blind pouch
If there’s a fistula:
Gastric distension(air in stomach on CXR)
Reflux>aspiration pnemonia>respiratory distress
Treatment of esophageal atresia
Surgical repair
Prognosis of surgery for esophageal atresia
1.Sometimes residual dysmotility
2.GERD
Two phenomenon occurs during midgut development:
Herniation
Rotation
Physiological herniation is
When contents of mid gut exits the abdomen and then return
Rotation of gut is when:
Contents of mid gut rotates around SMA
When does physiological herniation occur and why
6th week of development
It occurs because the abdomen temporarily becomes too small leading to hernaition of intestine through the umbilical cord.( visible on U/S)
When does the herniation reduce
10th week of development
What happens if the midgut does not return to the abdomen?
The baby will be born with omphalocele
What’s an omphalocele?
Persistence of normal herniation
Intestines will be outside the abdomen covered by membrane
What’s the difference between simple and liver containing omphalocele?
When the membrane only contains intestines it’s simole omphalocele.
When liver is also present then it’s the latter one.liver herniates because the lateral folds fail to fuse
Key features of omphalocele that distinguishes from gastroschisis
Covered by peritonium
Herniates through umbilical cord
Babies with omphalocele has
Normal GI function
Many genetic defects(trisomy21(down syndrome,18edward syndrome,13)
Many associated conditions(conginetal heart defects(upto 50% of babies)
Orofacial clefts
Neural tube defects
Gastroschisis is
Extrusion of bowel through abdominal wall
Key features that distinguishes from omphalocele
Paraumbilical defect usually on the right side of umbilical cord
Not covered by peritonium
Mechanism of gastroschisis
Incomplete closure of abdominal wall
Features of gastroschisis include
Poor GI function as the intetstine is damaged when it comes outside the abdomen(often associted with atresia,stenosis)
Few associated defects
If GI function restored good prognosis
Rarely associated with down or other conginital disease
Treatment of gastroschisis
Surgical reduction
The ectoderm forms
The skin
The CNS
The neural crest cells(gangion cells present in myenteric plexus of GI tissue)
What does the notochord form
Nucleus pulposa
What does the paraxial mesoderm form
Sclerotome
Dermatome
Myotome
What does the intermediate mesoderm form?
Urogenital system
The lateral plate mesoderm is divided into:
Splancnic mesoderm
Somatic mesoderm
What does splancnic mesoderm form?
Viseral peritonium,layers of gut loops like the mucous submucosa etc
What does somatic mesoderm form?
Parietal peritonium
Name three major branches of celiac trunk and their innervation
Splenic artery(spleen)
Left gastric artery(stomach)
Common hepatic (liver) which divides into cystic(GB) gastroduodenal(first part of duodenum) pancreaticoduodenal artery(pancreas)
Rotation of midgut results in
Normsl positioning of small bowel,colon
Cecum in right lower quadrant
Mal rotation of midgut results in
Bowel obstruction
Volvulus
Left sided colon
