hello anatomy colleagues this is dr alsup and in this video we will be discussing the
foundational concepts regarding the abdominal wall it's a surprisingly complex area and so
our discussions are going to regard the complexities of the layers of this region
there's a lot of layers surprisingly here and these are very functionally important
in protection due to the fact that there's really no bone to support the anterior and
anterolateral abdominal walls we're also going to spend some time on the neurovasculature
of the abdominal wall and we're going to introduce these this term of the umbilical
folds or peritoneal folds which we'll see on the deep surface of the anterior abdominal wall
so there's two major walls here that we're going to talk about there's the anterior and the
anterolateral and we'll start with anterolateral just because it's a little bit more complex there
we are not discussing the posterior wall here as this was discussed during the back
and spinal cord session however note it is only in the posterior portion of the abdomen
that you have that bony support with the vertebral column and the floating ribs 11 and 12.
so let's start on the sides or what we like to refer to as the anterolateral abdominal wall
and we're going to start superficial and make our way deep and walk through each one of the
layers so as as we know the most superficial layer is going to be the skin and then as always
deep to the skin we will have the superficial fascia and the superficial fascia is variable
amongst individuals and deep to the umbilicus or inferior to the umbilicus is a bit more complex in
this region with a mostly adipose layer but also a membranous portion and this deep membranous
portion is going to serve to better reinforce the portion of the wall which is lacking bony support
now next we're going to have the muscular layers and when we're talking the anterolateral wall
we're going to actually have three separate muscles so three separate layers of muscle and
we typically kind of collapse these as talking about the oblique muscles due to the direction
of their muscle muscle fibers but i want to note that the deepest muscle the transversus abdominis
the the muscle fibers are going to be directed more transversely or horizontally and not oblique
but like i said oftentimes we just kind of collapse these and talk about these as the
obliques now the directions of the muscle fibers are really important you think of kind of like
layers of plywood that are kind of put together to really reinforce this region and when these
muscles contract they may play a role in lateral flexion of the trunk think kind of
moving your trunk to the side or like an oblique type of crunch but most importantly these muscles
are important in overall maintenance of the tone of the abdomen so that really plays a
role in terms of protecting this region deep to these muscles are going is going to be
the transversalis fascia and really this is just the deep fascia of the transversus abdominis
but it will extend into the anterior region so we want to make note of that next you will have
the extraperitoneal fat and this is a variably sized layer typically there's going to be smaller
amounts of fat in the anterolateral portion and it will increase the more posterior you get
and the deepest layer of the wall will be peritoneum oh man you are going to love peritoneum
this is we're going to have a whole learning objective video to discuss details regarding
the peritoneum as it's very important in terms of the abdominal viscera and the entire abdominal
region but as a teaser the peritoneum is a serous membrane it's going to line the abdominal pelvic
cavity and the viscera within and it's similar to what we had with the pleura of the thoracic
cavity and you're going to love it we're going to have we're going to save more of the details
for later but be aware that this is going to be the deepest layer of the abdominal wall
now moving to the anterior wall the layers are actually
very similar to what we had in the anterior lateral wall but the biggest difference is
going to be the muscles that are present as well as this very dominant rectus sheath
instead of having three layers of muscles there's one dominant type of muscle in this region and
that's going to be the rectus abdominis muscles these are paired they're going to be on parallel
to one another they're very long very straight muscles and they actually extend all the way
from the xiphoid process way up here down to the pubic symphysis so again a very very long muscle
and interspersed throughout the muscle you're going to have
what's referred to as tendinous intersections that are going to attach to the anterior rectus sheath
so when this muscle is tensed or hypertrophied and there's a relatively small superficial fascial
layer this will give that six-pack appearance that can occur in the anterior abdominal wall
now the rectus abdominis muscles are going to be enclosed in the very dominant rectus sheath and
the the rectus sheath is going to be formed by the tendons actually of those anterior lateral
abdominal muscles so those tendons will extend all the way anteriorly and the tendons are very
flattened in this area and anytime you have a flattened tendon often these are referred to
as an aponeurosis so a flattened tendon i think an aponeurosis and like i said this
is going to enclose the rectus abdominis muscle the anterior portion of the rectus
sheath is going to be complete so it will extend all the way from xiphoid down to pubic synthesis
but the posterior kind of the posteroinferior portion of the rectus sheath
is actually incomplete so that would only leave transversal fascia and peritoneum in that region
now running right down the midline of the anterior portion of the rectus sheath is
what's referred to as the linea alba and this is kind of that white line of the median rectus
rectus sheath it's going to appear very opaque the rest of the rectus sheath is white as well
as most tendons are but it's not quite as opaque as what you have with the linea alba
okay on the deepest portion of the anterior abdominal wall think you're reflecting the
wall and you're looking at its deepest portion so the part that was closest to the viscera
and there are going to be these noticeable mounds kind of throughout this region and these
are called peritoneal folds and specifically in this region we actually kind of
refer to them as umbilical folds as well these are the same kind of things and these are do
we call these umbilical folds due to the very close relationship to the umbilicus
now these folds are created by structures that are covered with transversalis fascia variable
amounts of extraperitoneal fat and of course the parietal peritoneum and so the peritoneum
and those other structures are going to cover these ligaments kind of throughout these regions
so they're covering structures in this region with peritoneum so let's talk a little bit about
these deeper structures so the peritoneum is covering what we often refer to as ligaments now
we're using the term ligament here which i don't love because as we all know a ligament and typical
anatomical terminology means connective tissue connecting bone to bone however here a ligament is
used in a more general sense to indicate a tissue and in this case often a closed remnant of an
embryonic structure connecting two structures so we will be discussing several peritoneal ligaments
in this region as well as throughout the rest of the abdomen so that the ligament
thing is going to come up over and over again no we're not talking about some bones connecting to
bones but we're connect connecting structures basically so using it in its most general sense
now we'll start with the one that is unpaired it is running right in the midline and this
is referred to as the median notice the N here umbilical fold all right and this is covering
the median umbilical ligament so we have the term ligament here so something is connecting
something and in this case we are talking about the remnant of the fetal uracus and the uracus
connected the apex of the bladder to the umbilicus which is generally right around this region here
so this would connect to structures thus the term the ligament
so the remnant of the uracus is kind of left over and when you put peritoneum or light
peritoneum over this structure it creates this median umbilical fold
all right lateral to the median umbilical fold are the paired medial umbilical folds notice the
L so we're medial to the median umbilical fold and these are separated from the median umbilical
fold by the supravesical fossae so basically just these depressions on either side of the fold and
the medial umbilical folds are going to be formed by peritoneum overlying the closed or occluded
portion of the umbilical arteries and often this is referred to as the medial umbilical ligament
so the medial umbilical ligament is formed by the closed portion of the umbilical arteries
last but certainly not least are the lateral umbilical folds and i personally find these
the easiest to locate because typically you can see the inferior epigastric vessels which are
deep to the peritoneum this is what's forming the fold so this is not actually a case of peritoneum
lying over an embryonic structure the inferior epigastric vessels are very active very open
during adult life that's really what's supplying a lot of the abdominal wall region
now the fossae that are medial and lateral to the the lateral umbilical folds are really
important in terms of differentiating an indirect from a direct inguinal hernia
and we will discuss inguinal hernias in more detail in an upcoming video
but understanding the location of these umbilical folds are real a really important first step
okay moving on to the neurovasculature of the abdominal wall and we aren't getting
into any nitty-gritty detail here just big picture ideas and one of the most
important points i want to get across is that the nerves that innervate the abdominal wall do not
participate in plexus formation all right so this dermatome map when we're looking in this
region is going to be very similar to the peripheral cutaneous map all right and this
is because the ventral primary rami of the spinal nerves t7 through t12 and including L1 as well
will head directly to or from their target without splitting and forming nerves with fibers
from other levels so one spinal cord level will innervate kind of this same real estate throughout
and this is pretty unique as plexus formation is rampant throughout pretty much the rest of
the body other than the thoracic and the abdominal region the vpr of L1 does split into two branches
which run parallel to one another mostly you will have the superior partner which is going
to be the iliohapogastric nerve that's going to run superior to the pubic symphysis and then the
inferior partner which is the ilioinguinal nerve which has the distinction of being the nerve
that runs through the inguinal canal and we're having more details regarding that coming later
another note something that you often see come up on the boards is that the level of the umbilicus
or the belly button region is typically innervated by the vpr of t10 as you can see right here
and this understanding helps with getting the basics that
the general innervation pattern of the abdomen so t10 is at the belly button
superior to umbilicus is innervated by t7 through t9 and inferior will be t11 to L1
but i would put hearts and stars and whatever helps you remember that t10 is level of umbilicus
so like in all areas of the body the abdomen will have superficial vasculature and we
typically don't spend a lot of time in this area however i do want to pause here and talk about
one superficial vein in this area that may give insight regarding potential clinical conditions
and this is the superficial epigastric vein
the superficial epigastric vein is a tributary of the much larger
femoral vein but why i'm pointing this one out is that this vein will typically anastomose with the
para umbilical vein so just kind of focus on this portion of this image and the para umbilical veins
are small tributaries of the portal system so this is one of those portal caval or portal systemic
tributaries in this region we'll talk about that in more detail but with increased pressure in the
portal venous system such as with portal hypertension these veins in this region
may become dilated and the distention of the veins in this region is often referred to as caput
meduse due to its supposed similarities of medusa's head with that very distinct
head full of snakes extending laterally so these veins here can be noticeably varicose or distended
extending from the umbilical region but if not distended these veins are not particularly
noticeable here and we'll spend a lot more time discussing the portal venous system and these
naturally occurring portacaval anastomoses these are really interesting areas but it's when it
is when you have some issue like with portal hypertension that this can become noticeable
so we'll come back to this image in quite a bit more detail when talking about the liver
but the major vascular supply is going to be deeper and these are going to be the superior and
the inferior epigastric arteries and veins and the arteries and veins travel very closely together
as you can see in this image we have seen the superior epigastric arteries and veins previously
the superior epigastric artery is one of the two terminal branches of the internal thoracic
or internal mammary artery this is the one that looked like the continuation of that and this
will anastomose or communicate with the inferior epigastric artery and really it's the inferior
epigastric artery that's the major supplier of blood to this region this is going to be a
branch of the external iliac it branches off just superior to the inguinal ligament so you'll have a
communication of the inferior epigastric with the superior epigastric deep to the rectus abdominis
and this brings us to our summary slide so a lot of big picture concepts here
understanding the abdominal wall is vital to understanding the organization and visceral
pain patterns of the deeper abdominal viscera additionally being able to describe the layers of
the abdominal wall will help to work through the complexities of abdominal incisions so take your
time in this area and please as always reach out with any questions have a great rest of your day