Hello all this is Dr.
Kathleen Alsup, and I'm going to provide a quick overview of the liver.
The goals of this lecture are to provide you with the big picture ideas associated with the liver to better prepare you for your anatomy
dissection experience, but also importantly in terms of preparing you for
the clinical and other basic science lectures that are coming up in the gastrointestinal sequence.
Now as you probably know the liver is considered the largest gland in the body,
and it takes up a large portion of the abdomen. It is located predominantly in the
upper right quadrant of the abdomen, but it also extends into the left upper quadrant.
It has a very close association or relationship with the diaphragm, and you can't see the diaphragm here,
but recall in terms of our dissection in the respiratory sequence:
You had that diaphragm that you could see, and you could feel the liver just deep to the diaphragm,
so a very close relationship there. That's why that right dome of the diaphragm is more superiorly placed.
Functionally, it performs a wide range of metabolic activities required for homeostasis.
Nutrition, immune defense, and particularly important in terms of removal and breakdown of toxic or potentially toxic materials in the blood.
There are four gross anatomical lobes of the liver:
The right lobe is the largest. It's considerably larger and contributes to all surfaces of the liver.
The left lobe is the second largest lobe, and if you are just looking
into the abdomen you would only see the right and the left lobe of the liver.
Now in this particular view we're looking at the visceral, or the inferior surface of the liver,
so you can see the other two lobes associated.
You will have both of the caudate and the quadrate lobes available in this view.
The quadrate lobe is located anterioinferior,
and is in very close approximation to the gallbladder,
so when I'm trying to understand which one is which, I try to find that gall bladder if it hasn't been removed
and then I know that I'm looking at the quadrate lobe.
The caudate lobe is going to be located posterioinferior.
These lobes are different than the eight functional divisions,
which are based on the distribution of the portal venous branches in the parenchyma, and those particular
segments are not going to be visible in an intact view of the liver, just these four gross anatomical lobes.
There are considerable peritoneal attachments associated with the liver,
and we're going to go over some of the big picture ones and we're going to start with the falciform ligament.
You can see the falciform ligament right here in this image.
This attaches the liver to the anterior abdominal wall,
and when we're talking about within dissection,
that anterior abdominal wall will be reflected in order for us to be able to see all of the abdominal viscera.
So it'll already be cut and it will appear as a peritoneal flap between the right and the left lobes of the liver.
In the inferior border of that falciform ligament,
you'll have your round ligament, or ligamentum teres hepatis, and this
continues into a fissure on the inferior surface of the liver.
This is the remnant of the umbilical vein that in fetal life opens into the portal vein.
The diaphragmatic surface of the liver is covered with visceral peritoneum,
except posteriorly and what we refer to as the bare area of the liver,
and this is where the liver is attached to the diaphragm by areolar tissue, not by peritoneum.
The visceral peritoneum that covers the majority of the rest of the liver are what we refer to as
coronary ligaments and triangular ligaments.
One other area that I want to bring to your attention is what's referred to as
ligamentum venosum
and this is the obliterated venous connection between the left portal vein and the left hepatic vein,
and fetally this is referred to as the ductus venosus, and you can see the ligamentum venosum
sitting in the groove for the ligamentum venosum, so very aptly named, between the caudate and the left lobe.
Lastly in terms of peritoneal attachments are the subdivisions of the lesser omentum.
So, we're not talking greater omentum, which is by far the more significant portion.
We're talking about the lesser omentum, and recall the lesser omentum
is that double layer of peritoneum located between the lesser curvature of the stomach
to that inferior surface of the liver.
The hepatogastric ligament is located between the groove for the ligamentum venosum,
so remember, we just saw that on the inferior surface of the liver,
and it will extend all the way to the lesser curvature of the stomach.
The hepatoduodenal ligament is another division of the lesser omentum.
This is going to be between the porta hepatis
and the duodenum, and very importantly it encloses the portal triad, and that portal triad includes:
the hepatic artery proper, which is a branch of the common hepatic artery, the hepatic portal vein,
and the the common bile duct
(Sometimes you'll see the term common as well as bile duct, sometimes you'll just see bile duct)
and recall that this is a combination of the cystic and the common hepatic ducts.
So, let's discuss a little more in terms of the porta hepatis,
and this is this deep fissure on the inferior surface of the liver situated between
the quadrate and the caudate lobe posteriorly.
It's going to contain the portal veins.
You'll have the left and right branches of the hepatic artery,
and you will also have your right and left hepatic ducts
Additionally, and this doesn't get as much play, but it is very important in terms of what will be in located in this area,
you'll have the hepatic plexus of nerves and some lymph vessels in association with the porta hepatis.
The main arterial supply for the liver is going to be from the hepatic artery proper,
which is going to give off the right and left hepatic arteries,
and you can see those right in this region here associated with the portal triad.
It will branch right before it gets to the liver.
There are two Venus systems associated with the liver,
you will have the portal and the hepatic, or the portal or the systemic. You'll see it three different ways.
The hepatic portal vein is formed by your
superior mesenteric vein and the splenic vein, and that will be just posterior to the neck of the pancreas,
so a very important relationship there,
and it will divide, or you'll have two tributaries,
referred to as the right and the left portal veins, and that's how that is getting into the liver.
The parenchyma is going to be drained by the three main hepatic veins, formed by the union of collecting veins.
These are going to drain into the systemic system, or into the inferior vena cava, just inferior to the diaphragm.
The parenchyma of the liver is innervated by the hepatic plexus,
which is the largest offshoot of the celiac plexus.
This contains both sympathetic fibers and also, very importantly, parasympathetic fibers.
One other thing I want to note here is that the capsule that's goin g to surround the external surface of the liver
actually has innervation from the intercostal nerve,
so you do have some somatic nerves associated with this region as well.
This concludes the overview of the liver.
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