GI embryo flashcards
what happens on day 16?
gastrulation (epiblast forms the 3 layers:epi, meso and endoderm)
what layers contribute to the gut tube?/GI system?
All 3: endoderm, mesoderm, ectoderm
What does the endoderm form?
the epithelial lining from pharynx to the upper 2/3s pf the anal canal, and the epithelium of all the glands/organs that are extensions of the gut tube
What are the GI accessory organs/glands that form from the gut tube?
submandibular and sublingual glands, liver, pancreas and gall bladder
What does the mesoderm form in the GI system?
connective tissue, mesentary and smooth muscle
What does the ectoderm form in the GI system?
the nerves; and the epithelium in mouth and lower 1/3 of anal canal
what is Hirshsprung disease?
failure of the ectoderm’s neural crest cells to migrate to the caudal 1/3 of the colon–> resulting in megalocolon
how does the endoderm end up lining the inside of the gut tube?
folding of the embryo
what stays outside when the folding occurs?
the yolk sac and the allantois
remind me, what is the allantois and the yolk sac?
the allantois is a diverticulum of the gut tube near the cloaca, and becomes (mostly) the urinary bladder in the adult, the other part eventually becomes part of the umbilical cord by joining the vitilline duct (yolk sac stalk) and blood vessels but is initially on its own (partially in and out of the embryo); the allantois does nothing in humans and will degrad to wharton’s jelly in the umbilical cord with the vitilline duct; the yolk sac is thought to provide nutrients to the embro initially and is a place where gonadal stem cells reside for a while before going to their respective places
as an embryo, can fluids pass through the gut tube?
not initially, the tubes are blind-ended at the mouth and anus until the 5th and 7th weeks, respectively
what are the different portions of the gut tube?
foregut, midgut, hindgut
what part is the foregut in the embryo? The adult?
from the buccopharyngeal membrane through the pharynx to the liver bud; in the adult it goes from the pharynx to the 2ndpart of the doudenum (including the pancreas, liver and gall bladder
how is blood/nutrients mainly supplied to the foregut?
by the celiac artery
what part is the midgut of the embryo and the adult?
the lower 1/2 of the duodenum to 2/3 of the transverse colon; parts 3 nd 4 of the duodenum, small intestine, cecum, appendix, ascending and the rt. 2/3s of the transverse colon
what vessel supplies the midgut?
the superior mesenteric artery
what part of the gut tube in the embryo and adult form the hindgut?
lower 1/3 of the transverse colon to the cloacal membrane; the left 1/3 of the transverse colon to the upper 2/3s of the anal canal
what vessel supplies the hindgut?
the inferior mesenteric artery
how does the stomach develop and end up in it’s position with an anterior and posterior vagal trunk sandwiching it?
the dorsal aspect grows faster than the ventral surface, it rotates 90 deg around the vertical axis so that the rt vagus nerve becomes posterior and the left vagus nerve becomes anterior, the stomach also shifts to the left and rotates 45 deg in a coronal plane
What is formed due to the pulling of the dorsal mesentery as the stomach positions itself?
the lesser sac
what is the greater omentum formed from and how did it get there?
stretched out from the dorsal mesentery as the stomach rotated– it hangs off the greater curvature of the stomach and posterior wall
what is the general shape of the duodenum and how did it get that way?
it is a “c” shape– it is pulled superiorly and to the rt as the stomach rotates and the pancreas grows
what is the blood supply to the duodenum?
anastamoses from both the celiac and the superior mesenteric arteries
during the 2nd month, the lumen of the duodenum is obliterated, but then recanalized by apoptosis- if not recanalized a person will have what problem?
duodenal atresia or stenosis if partially blocked, or perhaps biliary atresia if the main pancreatic duct is blocked
what is the radiographic sign of duodenal atresia?
double bubbles separated from eachother by the pyloric sphincter
what happens if the main duct is blocked during recanalization?
Extrahepatic biliary atresia, a child may present with jaundice, dark urine and light stools
where do accessory abdominal organs develop from?
2nd part of the duodenum (where the main (with common bile duct material)and accessory pancreatic ducts enter the duodenum)
how does the liver develop?
grows out from the duodenum and enters the ventral mesentery and the septum transversum
what does mesenteric liver tissue become?
hematopoeitic, Kupffer and connective tissue cells (does hematopoeisis from weeks 8-30)
how does the pancreas form?
from two endodermal outgrowths (dorsal and ventral); the ventral swings around posteriorly and joins the dorsal bud
what part does the ventral pancreatic bud become?
the inferior part of the head and uncinate process
what does the dorsal bud become?
the superior part of the pancreatic head, the neck, body, and tail
the main pancreatic ampulla/duct arises from which pancreatic buds?
the entire ventral and the distal part of the dorsal bud
the accessory pancreatic duct/ampulla comes from which part of the pancreatic buds (if present)?
the proximal portion of the dorsal bud.
which other duct empties into the main pancreatic duct?
the common bile duct from the gallbladder’s bile duct and the hepatic duct
at about week 6, what part of the gut tube herniates through the umbilical ring?
the midgut, which is attached to the SMA (superior mesenteric artery)
When the midgut herniates initially, how much does it rotate?
90 deg around the SMA
when the midgut enters the abdominal cavity again, how much more does it rotate? How much total?
180 deg; 270 deg total
the jejunum enters 1st and the cecal bud enters last, but what else needs to happen to be in anatomical position?
the cecum needs to drop from the RUQ to the LRQ
what is the end of the hindgut called?
the cloaca
how does the cloaca become the urogenital sinus and the rectoanal canal?
a urorectal septum divides it, also making the cloacal membrane into an anal and urogenital membrane
if the hindgut only makes up the proximal 2/3 of the anal canal, what creates the lower 1/3?
invagination of the surface ectoderm
what is another word for the anal pit?
the proctodeum
what is the pectinate line?
it is the division between ectoderm and endoderm
what type of epithelium is found at the pectinate line?
columnar epi above, stratified squamous (non keratinized) below
what is the bl supply at the pectinate line?
superior rectal artery abv, middle and inf rectal artery blw
what is the lymph drainage at the pectinate line?
internal iliac and inf mesenteric lymph nodes abv, superficial inguinal lymph blw
what is the innervation round the pectinate line?
hypogastric plexus abv, inf rectal nerve branching from the pudendal nerve blw
what is the bl drainage around the pectinate line?
sup rectal vein abv, middle and inf rectal vein below
what happens when the vitilline duct persists?
you have a meckel’s diverticulum
what ectopic does a Meckel’s diverticulum usually contain and why is this bad?
ectopic gastric and pancreatic tissue, HCL is produced and you have ulceration and bleeding
where are Meckel diverticulums normally found?
about 2 feet from the iliocecal valve
how big are they?
2 inches long
in whom does it occur more frequently?
2x more in males
how frequently does it occur?
2% of the population affected
when does it normally present?
at 2 yo
What else is associated with vitilline persistence?
vitilline cysts and fistulas
what happens when the allantois remains patent?
you have a urachal fistula (with urine leaving the bladder) or at least a urachal cyst
why are respiratory and esophageal problems often occur together?
because the lung bud is created from the same endoderm that forms the esophagus
what happens when there is incomplete separation of the esophagus and trachea?
you get polyhydraminos bc the fetus cannot swallow; this is called an esopha
what are the birth defects in women who take progesterone-estrogen contraceptives during gestation?
VACTERL: vertebral, anal, cardiac, tracheal, esophageal, renal, limb abnormalities
what is it when the pancreas wraps around the entire duodenum during development?
the Annular pancreas can cause duodenal stenosis
define gastroschisis
guts come out of abdominal cavity into the umbilical cord with an associated rupture of the amnion
the duodenum is behind what structure?
the transverse colon
define omphalocele
failure of the midgut to return to the abdominal cavity – still covered by amnion
define umbilical hernia
failure of the umbilical wall and intestines are covered by skin/subcutaneous tissue
malrotation problems:
non-rotation, reversed rotation (situs inversis) and subhepatic cecum and appendix
what causes a volvulus and what is it?
it is a twisting/cutting off of circulation to a portion of the gut generally because of mobile segments of the intestines move
what might happen when there are problems with urorectal septum formation?
rectourethral fistula, rectovaginal fistula, imperforate anus, persistent cloaca rectocloacal fistula, etc
problems: intestinal duplication
=rare
problem: anal stenosis
=hindgut anomaly
