Lecture 24: Embryology of the Digestive System and Foregut Flashcards
components of digestive tube
mouth, pharynx and esophagus, stomach, small intestine (duodenum, jejunum, ileum), large intestine (cecum, colon, rectum, anal canal, anus)
accessory organs to digestive process
teeth, salivary glands, liver, pancreas
when primordial gut begins to develop
beginning of week 4
beginning of digestive tract
orophorengeal membrane, made of ectoderm and endoderm
stomodeum
orophorengeal membrane other name
fibroblast growth factors
establish anterior/posterior positioning of primordial gut
what signals for induction of endoderm
FGF-4 and activins
what does endoderm do in primordial gut formation
specifies temporal and positional information
derivatives of the foregut
primordial pharynx and derivatives (oral cavity, pharynx, tongue, tonsils, salivary glands, upper respiratory system)
lower respiratory system
esophagus and stomach
duodenum proximal to bile duct
liver, biliary appartus, pancreas
what separates esophagus?
T-E septum
makeup of esophagus
upper 1/3: striated muscles from pharyngeal arches
lower 1/3: smooth muscle from surrounding splanchnic mesenchyme
nerve supply to esophagus
CN X
main blood supply to esophagus
celiac trunk
epithelium effect on developing esophagus
obliterates the lumen but it then recanalizes
T-E septum during esophagus development
separates T-E structures
esophageal stenosis
narrow esophagus
due to incomplete recanalization during 8th week or failure of esophageal blood vessels to develop
when does stomach develop
week 4
shape change of developing stomach
tubular structure dilates –> fusiform enlargement
direction fusiform enlargement of stomach develops
anterior to posterior
posterior part of developing stomach
greater curvature
grows faster, toward vertebral column
anterior part of developing stomach
lesser curvature, grows slower, toward anterior abdominal wall
rotation of develop stomach
weeks 4-6
90 degrees in a clockwise fashion
innervation of stomach wall
vagus nerve
L vagus: anterior
R vagus: posterior
dorsal mesogastrium
aka greater omentum
dorsal mesentery of stomach region, suspends stomach to posterior abdominal wall during rotation/development
dorsal mesogastrium creates
an omental bursa as it rotates to left during stomach rotation
ventral mesogastrium
suspends stomach and duodenum to liver and ventral abdominal wall
omental bursa
big hole formed by clefts in dorsal mesogastrium that coalesce
allows movement of stomach
greater omentum
layers of dorsal mesogastrium elongate and fuse, become greater omentum- fatty sheath lining abdominal cavity
what is enlarged in overweight people
omentum - becomes very fatty
congenital pyloric stenosis
extreme narrowing of pyloric lumen of pyloric canal- muscular valve- so food passage is obstructed
results in projectile vomiting
3/1000 births, more males than females
derivation of duodenum
begins week 4; continues into 5-6
dually derived from: foregut proximal to level of bile gut & mudgut
has dual blood supply
blood supply to duodenum
celiac artery
superior mesenteric artery
duodenum rotation
loop projects ventral, rotates to the right
duodenum recanalization
week 5-6, lumen becomes obliterated, then recanalizes
duodenal stenosis
partial occlusion of duodenal lumen, due to incomplete recanalization from defection vacuolization
causes back up in stomach and so stomach contents/bile are vomited
duodenal atresia
complete occulsion, very atretic, so hardly any duodenum; in segment, and no recanalization
can happen in 1 or more duodenum segments
20-30% of cases- associated with Down syndrome
polyhydramnios
duodenal atresia that causes build up of excess amniotic fluid in amniotic cavity, so on U/S see dark bubble next to stomach
hepatic (ventral) diverticulum in foregut occurs/becomes
week 4, becomes liver (large part) and gall bladder (small part)
induction for hepatic diverticulum
fibroblast growth factors from heart that act on bipotential cells
derivation of hepatic diverticulum
epithelium, distal end of foregut
derivates of mesdoerm of septum transversum
hematopoietic cells, kupffer cells, conenctive tissue cells
derivation of ventral mesentery
mesoderm of septum transversum that becomes lesser omentum and falciform ligament
derivation of common bile duct
connection between hepatic diverticulum and foregut
gall bladder function
stores secretions from liver, emulsifies lots of fatty type foods
kupffer cells
liver macrophages derived from mesenchyme in septum transversum
derivatives of mesenchyme in septum transversum
kupffer cells and hematopoetic tissue
derivatives of endodermal cells in hepatic diverticulum
hepatic cords > sinusoids
right or left lobe of liver bigger?
right
hematopoiesis in liver occurs
6 weeks
bile formation in liver occurs
12 weeks
stalk of diverticulum derivative
cystic duct
bile duct connects
hepatic and cystic ducts to duodenum
movement of common bile duct
entrance of common bile duct moves posteriorly with stomach rotation
ventral mesentery derivatives that persist
falciform ligament, lesser omentum = hepatogastric ligament, hepatoduodenal ligament
hepatogastric ligament connects
liver to abdominal wall
ventray mesentery forms
visceral peritoneum of liver
accessory hepatic ducts
variation in liver lobulation, usuall asymptomatic, matters during surgery
extrahepatic biliary atresia
1:10000 to 1:15000 incidence; due to failure of ducts to canalize or fetal infection
pancreas derivation
2 bus of foregut endodermal cells
how pancreas forms
duct of dorsal (larger) bud and ventral bud of foregut rotate posteriorly, fuse, form main pancreatic duct
location of pancreas
dorsal abdominal wall
growth factor for ventral pancreatic bud
FGF-2
growth factor for dorsal pancreatic bud
notochord secretes activin and FGF-2
exocrine histogenesis of pancreas
endodermal tubules branch, form acinar cells and ducts
endocrine histogenesis of pancrease
clumps of cells from exocrine part form islets
annular pancreas
if portion of ventral pancreatic bud that goes anteriorly improperly fuses around duodenum, causes duodenal obstruction
derivation of spleen
mesenchyme within dorsal megogastrium
gastrosplenic ligament
connects stomach to spleen
spleen functions
hematopoiesis, immune system
accessory spleen
10% incidence, associated w/ heart disease
