In this lecture on foregut development,
we’re gonna discuss how to various glands associated with the foregut,
the liver, the gallbladder, and pancreas
develop from the endoderm that lines the gut tube.
Now, during the third week of development,
a bud off of the foregut called the hepatic diverticulum develops.
This is also sometimes called the liver bud and it will indeed become the liver.
It’s gonna grow anteriorly into the septum transversum
and it will eventually form the liver.
The septum transversum and the hepatic diverticulum
contribute different tissues to the developing liver.
So they are both necessarily.
The connection of the hepatic diverticulum to the foregut
is gonna become the common bile duct.
And if you think about the mature anatomy,
the common bile duct does indeed connect the liver
to the foregut at the descending portion of the duodenum.
Now, one bud was not enough for our hepatic diverticulum
and yet, another bud develops off of it.
The gallbladder is gonna develop as an out-pouching of this common bile duct
and is going to develop on the inferior surface of the liver,
much like its location in the mature adult on the underside of the liver.
The connection of the gallbladder to the common bile duct
will become the cystic duct.
So at the point, we’ve already got the connections
between the liver, gallbladder, and duodenum established.
Now, if the cystic diverticulum to create the gallbladder weren’t enough,
we develop two more buds coming off of the foregut.
Just inferior to the cystic diverticulum is the ventral pancreatic bud.
And if there’s a ventral pancreatic bud, it should be a surprise to no one
that there is also going to be a dorsal pancreatic bud.
These two separate developments off of the foregut
are gonna be brought together by rotation of the stomach and migration of the liver.
As those organs develop, enlarge, and rotate,
the ventral pancreatic bud, cystic duct,
and common bile duct are all moved into a posterior position
and if you know your anatomy, you may remember that the common bile duct
enters the duodenum on its posterior side.
That’s a remnant of this set of rotations.
So by the time we’re done,
we’ve got the gallbladder developing on the underside of the liver,
the ventral pancreatic bud has swung posteriorly
and fused with the dorsal pancreatic bud making a single pancreas.
The main pancreatic duct is going to be the remnant of the drainage system
and connection to the duodenum of the ventral pancreatic bud.
Whereas the accessory pancreatic duct
is what’s left of the connection of the dorsal pancreatic bud to the same region.
Occasionally, the accessory pancreatic duct will rescind
and the pancreas will have one and only one outlet
for its secretory products into the duodenum.
I should note that because of this rotation and fusion of the pancreas,
the ventral pancreatic bud is gonna create the uncinate process
and part of the pancreatic head.
Whereas the dorsal pancreatic bud
is going to form the rest of the pancreatic head, its body, and its tail.
Things that can go wrong in this process include poor migration of the pancreas
and most commonly, this manifests as a pancreatic ring.
In this case, a portion of the ventral pancreatic bud goes posteriorly like we’d expect
but another portion travels anteriorly
and forms a continuous ring around the duodenum
as it attaches to the dorsal pancreatic bud.
This results in what’s called an annular pancreas or a ring-shaped pancreas.
That in it of itself is not problematic.
The problem is it constricts the duodenum and narrows its lumen.
So this must be differentiated from other reasons
for duodenal atresia or duodenal stenosis.
Because the pancreas develops off of the endoderm in a specific location
due to the signals that are present in that location,
those signals can induce the formation of pancreatic tissue in other places
such as the small intestine or the stomach.
Problems with the gallbladder and its drainage can be very serious.
Failure of the gallbladder to form in the first place is gallbladder agenesis.
This is actually not as severe as you might think
because the bile that the liver produces can still drain to the small intestine and be expelled.
You can have the gallbladder develop in an unusual location.
A sessile gallbladder may occur when it develops directly off the common bile duct
and there’s no cystic duct.
Just complete immediate connection between the gallbladder and the common bile duct.
You can also have an additional pouch
developing off of the gallbladder called a Hartman’s pouch.
Again, not a problem that you encounter due to itself
but maybe a problem when you’re doing surgery to remove a gallbladder
and have to account for an unusual drainage pattern
or an unusual shape of the gallbladder.
Those variants are typically asymptomatic
as are small little additional bulbs
coming off the top of the gallbladder such as a Phrygian cap,
a midline separation inside the gallbladder called a Septate gallbladder
where there is in fact a little wall or septum within.
You can have duplication or double gallbladders, not problematic,
but if you’re trying to remove a gallbladder,
you may have to be prepared to find two of them in that location.
And occasionally, the gallbladder forms so high off of the common bile duct
and in such close coordination with the hepatic diverticulum
that it’s actually located within or partially within the liver
and in this case, to remove the gallbladder can be problematic
since you have to make sure you’re not lacerating the liver in the process.
Problems with the drainage of bile from the liver can be very, very serious.
The liver produces bile and it does not stop
and if that bile cannot drain to the common bile duct and intestine
or be held temporarily in the gallbladder,
it has no choice but to back up into the vascular system
causing jaundice, damage to the liver, and eventual death
So absence of the entire biliary system, biliary atresia is incredibly important
and it causes immediate jaundice of an infant.
Now, jaundice is a typical presentation in infants and will typically resolve
but it does need to be tracked
and the cause of that jaundice, properly identified.
Partial atresia of the bile duct can also occur, leading to the same problem.
If the bile cannot leave the liver and get to the intestine,
it will cause jaundice, cirrhosis, and eventual death.
Other things that are not as problematic are aberrations in the biliary tree
that still allow it to drain into the intestine.
An accessory bile duct that enters the gallbladder directly can be found
and has to be accounted for during gallbladder removal
and what is known as a choledochal cyst
can occur when you have ballooning of part of the biliary tree.
These must be accounted for and can cause problems
but are not as severe as problems
that cause jaundice, cirrhosis, and death due to backup of bile.
Lastly let’s come to the development of the spleen.
The spleen is derived from mesenchymal cells which are found
between the layers of the dorsal mesogastrium.
Its characteristic shape is obtained very early in development
and is retained during adult mature form. Because of the rotation
of the stomach, the mesogastrium fuses with the peritoneum over the
left kidney. This forms the lienorenal ligament. Moreover, because
of this rotation, the splenic artery is found to have a course
behind the peritoneum on its way to the spleen. The mesenchymal
cells of the spleen differentiate into splenic capsule,
connective tissue, and parenchyma. The spleen is a major
hematopoietic organ in fetal life. It is involved with the
production of lymphocytes and monocytes during adult life.
Thank you very much for your attention and we’ll return to finish up on foregut development.