Embryo of GI tract Flashcards
What tissue layer makes up the epithelial lining and glands of the GI tract?
Endoderm
During lateral folding, what is incorporated as the embryonic midgut?
yolk sac endoderm
What tissue forms the smooth muscle and connective tissue of the GI tract?
Splanchnic mesoderm
What is the peritoneum?
The serous membrane lining the abdominal cavity (parietal) and organs (visceral)
What is the mesentery?
A double layer of peritoneum that suspends an organ from the body wall (it can contain CT blood vessels, lymphatics and nerves
How are organs suspended from the body wall?
via the mesentery
What creates mesenteries?
lateral folding
What is the splanchnic mesoderm responsible for?
smooth muscle and connective tissue of the GI tract (including mesenteries)
What is the ectodermal contribution to the GI tract?
neural crest cells
What are neural crest cells responsible for in the GI tract?
They form the enteric nervous system
T/F all three germ layers contribute to the GI tract?
truth
T/F the GI tract is divided into the foregut, midgut, and hindgut regions?
true
What artery supplies the pharynx?
the pharyngeal arch arteries
What artery supplies the foregut?
The celiac trunk
What artery supplies the midgut?
The superior mesenteric artery (SMA)
What artery supplies the hindgut?
The inferior mesenteric artery (IMA)
What is the developmental structure that will eventually become the trachea, respiratory tree and lungs?
The respiratory diverticulum (appears on the ventral side of the foregut)
Which side of the stomach is the greater and lesser curvature on?
Greater curvature is on the dorsal side
Lesser curvature is the ventral surface of the stomach
T/F the stomach undergoes 90 degree clockwise rotation if looking from above?
truth
How does this affect the position of the greater and lesser curvatures?
Lesser curvature (ventral) ends up on the right side and the greater curvature (dorsal) ends up on the left
Because of stomach rotation in development, which nerve supplies which part of the stomach and why?
Well, the nerves travel with the stomach as it turns, so the right vagus nerve supplies the dorsal stomach which is on the left and vice versa
Where does the spleen form?
Between two leaves of the dorsal mesogastruim
As the stomach rotates the dorsal mesogastrium is carried to the _____ side.
Left (just follows the rotation of the stomach)
What important structure follows the dorsal mesogastrium as it is carried to the left?
The spleen
Understand stomach rotation and mesogastrium repositioning
Okay.
Where is the duodenum?
It is the C-shaped loop just distal (on its way out) to the stomach
The duodenum is made up of what two portions of the gut?
Proximal half is the foregut and the distal half is the midgut
Which organs are secondarily retroperitoneal?
distal duodenum
pancreas
What does the hepatic diverticulum give rise to? (3 things)
It gives rise to the:
liver
gall bladder
bile ducts
Where does the hepatic diverticulum arise from (what tissue) and where at in the gut? Where does it travel?
It emerges ventrally from the endoderm of the distal foregut and grows superiorly toward the septum transversum
T/F- as I look out the window while making these cards, there is a snowstorm going on.
Trooth.
How does the pancreas get its developmental start? (tissue, location)
It emerges from the distal foregut as two endodermal buds- one dorsal and one ventral
T/F as the duodenum rotates, the ventral bud swings in a clockwise direction until it fuses with the dorsal bud?
Truth
When the ventral bud of the pancreas fuses with the dorsals bud, what does it become? (2 things)
the uncinate process and the inferior portion of the head of the pancreas
The main pancreatic duct is made up of what?
The distal portion of the dorsal bud duct and the ventral bud duct
What is the accessory pancreatic duct made up of?
the proximal dorsal bud duct
What is an annular pancreas?
When the ventral bud develops, it has two portions that usually fuse before rotation. If that doesn’t happen each portion can wrap around the duodenum, creating an obstructive ring
T/F, the midgut forms a U-shaped loop
true
The cranial limb of the midgut contains what three things?
distal duodenum
jejunum
proximal ileum
The caudal limb of the midgut contains what four things?
distal ileum
cecum+appendix
ascending colon
proximal 2/3 of transverse colon
What is a physiological umbilical hernia and what causes it?
Caused by insufficient room in the abdominal cavity, it is a temporary herniation of the midgut loop in the proximal umbilical cord
What is congenital omphalocoele?
It is a persisting umbilical hernia where the viscera is covered by the amnion and is within the proximal umbilical cord
T/F gastrochisis involves the umbilical cord?
false
The midgut rotation rotates which way, how much, happens when, and what is the axis of rotation?
Counterclockwise 90 degrees
during week 6
superior mesenteric artery (SMA) is the axis
When does the 2nd midgut rotation occur?
During week 10
What does the 2nd midgut rotation accomplish?
the 180 degree CCW rotation brings the intestines into their normal position
What is the total counterclockwise rotation of the midgut?
270 degrees
T/F the ascending and descending colon become primarily retroperitoneal?
False- secondarily retroperitoneal
What happens if there is nonrotation of the midgut?
The caudal limb returns first and you get a left-sided colon
What happens in reversed rotation of the midgut?
The first rotation happens normally and the second rotation is reversed resulting in a net 90 degree clockwise rotation.
What is volvulus?
it’s where abnormal rotation causes the intestinal loop to get all tangled up and can result in bowel obstruction or compromised blood flow
What is the definition of stenosis?
The abnormal narrowing of a lumen/orifice (for a tubular organ or structure)
What is atresia?
The condition in which a body or lumen or orifice is abnormally closed or absent
What is a fistula?
An abnormal passageway between two organs/vessels or between an organ and the external environment
T/F the intestines (specifically the midgut loop) become temporarily occluded?
True
What could cause stenosis or atresia in the duodenum?
failure of the lumen to recanalize by the end of week 8
What is the most common GI malformation and what does it cause?
Meckels (ileal) diverticulum. It causes ulcers and bleeding
What partitions the cloaca?
A urorectal septum
What divides the cloacal membrane into the urogenital and anal membranes?
A urorectal septum
The cloaca is partitioned into what to things?
The urogenital sinus ventrally and the anorectal canal dorsally
An aganglionic portion of the colon is caused by and called what?
Caused by neural crest cells failing to migrate to form the enteric nervous system. Called Hirschsprung’s disease
