Embryology Flashcards
What 2 things does embryonic folding incorporate into the embryo?
Gut tube
coelom
What’s the deal with the mesenteries?
They surround the primitive gut tube as coelomic sacs…initially there is a dorsal & ventral mesentery–>then just a dorsal eventually
The primitive gut tube is connected to what?
the yolk sac
the connecting stalk is significant
When the folding is occurring to get the gut tube…what gets pinched off? WHat connects these 2 structures at first?
Yolk sac gets pinched off
vitelline duct
Where do the mucosa & glands of the GI come from?
the endoderm inside the gut tube!
Where do the smooth muscle & CT that surround this come from?
splanchnic mesoderm of the lateral plate
What composes a mesentery?
2 layers of peritoneum w/ underlying nerves & blood vessels
What are the 3 main regions of the embryo? And their blood supply?
Foregut: Celiac Trunk
Midgut: SMA
Hindgut: IMA
Describe the growth of the foregut.
It grows out & to the side. Think about the curve of the stomach.
In the foregut what is something special that isn’t present in other places?
Ventral mesentery–>provides support for things like the liver bud & gallbladder
When you have a ventral mesentery, like in the foregut–>is the dorsal mesentery continuous or discontinuous?
It is discontinuous. b/c the 2 sacs are still separated.
What are the 2 portions of the ventral mesentery that remain in the adult?
lesser omentum
falciform ligament
The dorsal mesentery grows quickly & folds on itself becoming the ______.
greater omentum
In the foregut the only way to get to the right coelomic sac is thru the _______.
epipleural foramen
Describe what the falciform ligament does.
It is a piece of mesentery. The placental blood travels along the anterior body wall & along the ligament & goes into the liver.
Is there a ventral mesentery in the midgut or hind gut?
NO. only in the foregut
Where does the region of the foregut end?
after the 2nd part of the duodenum
What does it mean to be primarily retroperitoneal?
It means that you never had a peritoneum.
What does it mean to be secondarily retroperitoneal?
It means that you initially had a peritoneum, but you lost it.
What does it mean to be peritonealized?
to be intraperitoneal
Is there something in the peritoneal sac?
No…except sorta during menstruation.
What are some primarily retroperitoneal structures?
Gut tube: distal portion of the rectum anal canal Non-gut tube: kidneys/urogenital system
What are some secondarily retroperitoneal structures?
ascending & descending colon
pancreas
2nd & 3rd portions of the duodenum
Where does the foregut end?
right after the pancreatic duct comes in
Where does the midgut begin & end?
Begins after the pancreatic duct & ends at the splenic flexure.
Aside from the midgut, what else ends @ the splenic flexure?
the vagus!!
Where does the hind gut begin & end?
begins @ splenic flexure & ends @ proximal anal canal
Describe the rotation of the foregut.
The stomach rotates 90 degrees, with the anterior surface turning toward the right.
Greater curvature grows faster than the lesser curvature…
The right coelomic sac gets bigger & the left one gets smaller.
What happens to the anterior surface of the foregut during the 90 degree rotation?
Anterior surface is the lesser curvature…it moves right
What happens to the posterior surface of the foregut during the 90 degree rotation?
Posterior surface is the greater curvature…it moves left
What happens to the ventral mesentery with the rotation of the foregut?
What forms the greater omentum?
The ventral mesentery ends up on the right side.
The greater curvature forms the greater omentum with the expansion of the dorsal mesentery as it must grow faster to keep up with the greater curvature.
Where is the lesser sac?
the space behind the lesser omentum
What connects the lesser & greater sacs?
epiploic foramen
How many layers is the greater omentum?
4 layers
What connects the stomach to the liver?
What connects the liver to the body wall?
Stomach–>Liver: Lesser Omentum
Liver–>Body Wall: Falciform Ligament
Which buds & things are attached to the duodenum?
liver, gallbladder, ventral pancreatic bud (attached to same place)
other side: dorsal pancreatic bud (off the dorsal mesentery)
How are the liver & gallbladder buds connected?
Gallbladder bud has a cystic duct
Liver bud has a hepatic duct
Together they form the common bile duct
With rotation…what happens to all of the pancreatic buds & the bile ducts?
The ventral pancreatic bud rotates & joins the dorsal pancreatic bud.
The ventral pancreatic duct dominates & what’s left of the dorsal pancreatic duct becomes the accessory pancreatic duct.
The bile duct swings around too…& the pancreatic duct & bile duct merge @ the duodenal papilla.
Describe the midgut rotation.
this loop of the midgut exits the abdominal cavity on the 5th week & doesn’t come back until like the 8-10th weeks.
It undergoes a 270 degree rotation around the SMA as its central axis.
It rotates in a counterclockwise direction if you are looking at the anterior surface of the baby.
The caudal half of the midgut loop gives rise to which structures?
cecum, ascending colon, transverse colon
Which part of the bowel gets trapped underneath the SMA as a result of the rotation?
the fourth part of the duodenum
After the 270 degree rotation, where does the last part of the rotation take place? When does it take place?
in the abdominal cavity
starts @ the 10th week
What is a volvulus?
It is the rotation of the gut or abnormal movement of the gut such that it causes a constriction of a portion of the blood supply. It can cause gangrene.
What is gastroschisis?
This is where the lateral walls of the abdomen don’t close completely…The GI gets thru the opening…
It isn’t covered by amnion, so exposed to amniotic fluid. Not associated w/ other defects.
What is omphalocele?
This is where the bowel goes out of the abdominal cavity around weeks 6-10 but it doesn’t come back like it should.
In this case, it is covered in amnion, & isn’t exposed to amniotic fluid.
However, this condition is associated w/ other birth defects.
What is the most common GI developmental abnormality?
Meckel’s diverticulum-in the ileum
an outpouching, a portion of the vitelline duct persists.
It can cause ulceration,perforation, & bleeding but usu it is asymptomatic.
What is the rule of 2s with Meckel’s diverticulum?
2% of the population has it
It occurs 2 feet from the ileocecal valve
It is 2 inches in length.
It is only symptomatic in 2% of the population.
It has 2 types of ectopic tissue: gastric & pancreatic
2 years is when you usu see it
2X as common in males
What types of nerves supply the portion of the hind gut below the pectinate line?
somatic
cutaneous nerves
Do internal or external hemorrhoids hurt more?
EXTERNAL b/c they are below the pectinate line
Describe hind gut development.
It starts off as the cloaca (a common sac b/w the urogenital & GI)
It has a urorectal septum separating them.
When this separation doesn’t exist–>problems.
Above Pectinate line: endoderm
Below Pectinate line: ectoderm
What is Hirschsprung disease?
is a failure of migration of neural crest cells into the developing gut tube. Usually affects the rectum and sigmoid colon and results in a section of the gut tube which is lacking ganglia and unable to contract
