hello everyone and welcome my name is dr glenn fox and let's talk about the duodenum
in this video we'll discuss the basic structure features and orientation of the duodenum
the duodenum is a c-shaped organ which is preceded by the stomach and succeeded by the
jejunum of the small intestine in fact the duodenum is the first part of the small intestine
the duodenum consists of four parts these are numerically enumerated and named and they can
also be named by their relative positions so for instance the first part of the duodenum
is contiguous with the pyloric part of the stomach if you recall the L1 vertebral level
is at the trans pyloric plane and that is the level at which the pylorus is going to feed
into the duodenum so the stomach is going to eject chyme into the duodenum for further chemical
digestion and absorption the first part of the duodenum or the superior part of the duodenum
is relatively short it's about five centimeters the first part of the first part so the first
half is intraperitoneal as is the stomach is intraperitoneal and it transitions into
a secondary retroperitoneal meaning it is behind the peritoneum and it is drawn behind
the peritoneum as part of its development the first part of the duodenum is relatively unique
from the remainder of the duodenum in that it is smooth-walled meaning that there aren't
circular folds or plicae circulares which are common throughout the remainder of the duodenum
the second part of the duodenum
here is also known as the descending part its orientation is vertical and it is highlighted by
having two duodenal papillae as well as for the first time plicae circulares or circular folds
the duodenal papillae are eruptions of the mucosa through which
secretions of the liver and gallbladder as well as the pancreas are going to enter
into the gut tube there is a major duodenal papilla the major duodenal papilla is the
distal of the two it receives the biliary tree as well as the main pancreatic duct
the hepatopancreatic ampulla empties through the major duodenal papilla and releases bile as well
as pancreatic juice into the lumen for further digestion the major duodenal papilla is quite
a landmark in that it divides the foregut from the mid-gut the minor duodenal papilla
is typically found proximal to the major duodenal papilla and if it is present it is what drains
the accessory pancreatic duct that accessory pancreatic duct drains the head of the pancreas
the circular folds or the plicae circulares are very strong circular shaped eruptions of
the mucosa that serve two roles the first is to slow the movement of material through the duodenum
and the second is to increase the total amount of surface area which allows for greater absorption
at its lowest extent the second part of the duodenum is at the L3 level and feeds into
the third part also known as the inferior part of the duodenum it's horizontal it crosses
at the L3 vertebral level and it is crossed anteriorly by the superior mesenteric vein
and superior mesenteric artery it is also secondarily retroperitoneal it also has
very strong circular folds and we can see that it's going to be nestled between the
superior mesenteric vasculature as well as the aorta and inferior vena cava
the third part feeds into the fourth part of the duodenum also known as the ascending part
it is also vertically oriented like the uh the second part uh the fourth part is the shortest
part of the duodenum it's about two and a half to three centimeters in length it is also
secondarily retroperitoneal it also has circular folds and its apex is supported by
the suspensory ligament of the duodenum also known as the ligament of Treitz ligament is
likely a misnomer for this structure it's predominantly composed of smooth muscle
tissue there can also be an accessory muscle to this suspensory ligament made of skeletal muscle
that will descend from the right crease of the diaphragm the suspensory ligament supports the
duodenal jejunal flexure that's where the fourth part of the duodenum transitions into the jejunum
and is sometimes used synonymously with duodenal jejunal flexure it may be of consequence to note
that this suspensory ligament is a landmark for categorizing gastrointestinal bleeds
any bleeds that are proximal to this are upper gi bleeds any bleeds which are distal
are lower gi bleeds the duodenum as a uh as a part of the gut tube
nestles about the head of the pancreas it snuggles it quite well and so we'll see that
the predominance of blood supply to the duodenum will be shared by the head and neck of the
pancreas and so when we think of this area we can think of the gastroduodenal artery which is a
branch of the common hepatic artery descending down and it's going to give rise to the posterior
superior pancreaticoduodenal as well as the anterior superior pancreatico uodenal artery
and the gastroduodenal will have many small duodenal branches supporting it
there's also the inferior pancreaticoduodenal from the superior mesenteric artery or the SMA
which is going to have both anterior and posterior branches which anastomose with
the anterior and posterior superior pancreaticoduodenal branches of the gastroduodenal artery
in addition jejunal arteries which we can see here coming
off of the left lateral side of the sma will also supply blood to the duodenum
in terms of innervation the autonomic innervation of the duodenum is relatively straightforward
when i think of autonomic innervation i typically think of the blood supply
because those autonomic plexuses follow the vasculature and this is now exception
so what we have is the pre-dominant blood supply to the duodenum will be
from both the celiac and the superior mesenteric plexuses keep in mind that
these plexuses are supplied by sympathetic fibers from the thoracic splanchnic nerves
and parasympathetic fibers from the posterior vagal trunk these fibers will form a plexus
and then will come out through the celiac trunk and the superior mesenteric artery
and the branches which serve the duodenum will have fibers from these plexuses
referred pain from the duodenum is transmitted along um
visceral fibers general uh visceral fibers from that accompany sympathetic fibers
and referred pain from the duodenum is referred to the epigastric region in terms of
the effects of the various portions of the autonomic nervous system on the duodenum
the parasympathetic stimulation is going to stimulate and enhance bowel motility
as well as lead to general vasodilation so we can think parasympathetic rest and
digest we have a very active duodenum sympathetic stimulation will lead to vasoconstriction as
well as the inhibition of bowel motility which would be quite the opposite of rest and digest
so we've discussed the duodenum its relationship to other viscera as well as
its relationship to the peritoneum its parts the features of their parts
its blood supply and its innervation this is your summary slide thank you for your time