Embryology and Anatomy of GI Flashcards
What makes up foregut?
pharynx
esophagus
stomach
liver
bile ducts, hepatic ducts
gallbladder
pancreas
proximal duodenum (until major duodenal papilla)
When are 3 major germ layers formed?
by end of 4 weeks of embryonic development (ectoderm, mesoderm, endoderm)
Where does esophagus develop from? (mid/fore/hind gut,etc)
from foregut:
tube - anterior part becomes trachea
posterior part becomes esophagus
separated by esophagotracheal septum
Which germ layers is esophagus composed of?
inner lining - endoderm (as is rest of foregut organs except spleen = all mesoderm)
muscular parts of esophagus - splanchinic mesoderm
(splanchinic means “organ” in Greek)
upper 1/3ish - striated muscle, lower 2/3 - smooth muscle
What are some of the possible congenital abnormalities of the esophagus?
- spectrum
- usually due to deviation of the tracheesophageal septum (division between esophagus (posterior) and trachea (anterior)
- polyhydroamnios = excessive amniotic fluid surrounding fetus (because fetus does not swallow it)
- after birth, vomiting = difficult passage of milk/no passage at all
- esophageal stenosis - narrowing of the esophageal tube
- esophageal atresia - closing of the esophageal tube - > no gas in abdomen on CXR
- tracheoesophageal fistula (TEF) - connection between esophagus and trachea -> air in stomach on CXR (H-type - fistula only)
* fistula = connection
- tracheoesophageal fistula (TEF) - connection between esophagus and trachea -> air in stomach on CXR (H-type - fistula only)
- esophageal atresia with transesophageal fistula => most common - blind sac in esophagus (atresia), lower esophagus connected to trachea (on right) - > drooling, choking, vomiting (b/c of fistula = blind pouch, food cannot enter)
- test by seeing if nasogastric tube can go into stomach
How is stomach developed?
- developed from foregut (tube), which enlarges to form stomach pouch
- dorsal border grows faster - greater curvature, ventral - lesser curvature
- stomach then rotates 90degrees to orient itself more left to right instead of front to back
- stomach attached to back of body - dorsal mesogastrium (mesoderm and gastrium=stomach) rotates with stomach and becomes site of spleen formation in between the two membranes (remember 90 degree move); attaches stomach to posterior wall before rotation
- ventral mesogastrium attaches stomach to anterior wall, liver develops between two layers of it
- then the most anterior part becoems falciform ligament (with umbilical vein) and the one between liver and stomach becomes lesser omentum
- (falciform ligament -> liver -> lesser omentum -> stomach)
What is the possible congenital stomach problem?
congenital hypertrophic pyloric stenosis
- hypertrophy of pylorus (circular muscles of the sphincter that divide stomach and duodenum) inhibit move of food between the two organs
- palpable “olive”-like mass in epigastric region
- non-bilious projectile vomiting (before liver so no bile) post-birth, polyhydroamnios - excessive amniotic fluid around fetus pre-birth
- treat with surgical incision
How is duodenum developed?
- from foregut (first part) and midgut (second part) - division at major duodenal papilla
- as stomach makes its 90 degree rotation, so does duodenum, into C shape
- first part has blood from celiac artery (because foregut) second part from superior mesenteric artery
- forms as a solid tube from epithelial cells, then middle atrophies inside to make lumen
- if lumen not resorbed properly, could have duodenal stenosis - partial blockage or duodenal atresia - full occlusion => polyhydroamnios (increase in amniotic liquid around fetus), vomiting post-birth with bile
How is liver, gallbladder and biliary duct system developed?
- from hepatic diverticulu (liver bud) that starts from foregut within ventral mesentary (remember 90 deg. rotation makes it go to the right)
- stroma of the liver (connective cells = Kupfer cells and hematopoietic tissue ) is from mesoderm of septum transversum (diaphragm!)
- part of the liver bud becomes the gallbladder
- bile ducts develop by occlusion and recanalization like duodenum
Malformations of liver and biliary apparatus?
estrahepatic biliary atresia => failure of biliary tree to recanalize (to develop lumen; re-canalize = restore flow)
bifid gallbladder: duplication of gallbladder = 2 present
How is pancreas developed?
- pancreas develops from 2 pancreatic buds (dorsal and ventral), which then fuse
- ventral bud is mostly pancreatic head and main pancreatic duct
- dorsal bud is mostly body and tail
What are some pancreatic developmental abnormlaities?
- annular pancreas: annular = ring shaped, the two pancreatic ducts not rotating correctly (usually ventral one has to rotate), so pancreas ends up forming a ring around duodenum and constricting it
- accessory pancreatic tissue can get into stomach, duodenum or ileum during development and secrete pancreatic enzymes from these ectopic sites
- pancreas divisum - ventral and dorsal parts fail to fuse (usually at 8 weeks) = divided!
How is spleen developed?
part of foregut ! but… from mesoderm unlike all other foregut organ linings
developed between two layers of dorsal mesogastrium (and rotates 90 deg to left)
grows in series of lobules which then fuse together, these sites of fusion can often be palpated
What is blood supply and innervation of foregut?
artery: celiac trunk on aorta (top one) at T12ish (superior mesenteric is L1, inferior L3 = think digestive blood flow basic: 1213
parasympathetic: vagus - turn on gut muscles, acid secretion in stomach
sympathetic: T5-9 (greater splanchnic nerve); inhibitory to gut muscles, transmit pain
structures: pharynx to proximal duodenum, including liver, gallbladder, pancreas and spleen
Which organs of GI are retroperitoneal (1’ and 2’ ry)?
Primary retroperitoneal: kidneys (incl. adrenal glands, ureters), aorta/IVC, lowest bit of esophagus, rectum
Secondary retroperitoneal: duodenum (excluding first 1/3 connected to stomach), pancreas, ascending and descending colon (but not transverse)
Mnemonic: SAD PUCKER - suprarenal glands, aorta/IVC, duodenum (last 2/3), pancreas, ureters, colon (ascending and descending), kidneys, esophagus (lower 1/3ish), rectum
