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Structures seen on the inferior view of the isolated liver.
Hello everyone! This is Megan from Kenhub, and welcome to another anatomy tutorial. In this tutorial, we will be looking at the posterior and inferior view of the liver paying particular attention to the visceral surface of the liver and the structures seen from this aspect. So, we’re going to explore the image seen here where we can see the posterior view of the liver or the view of the liver seen from the back of the body. We can also see the inferior aspect of the liver here.
Before we begin, I just want to quickly mention a few general points about the liver. As you know, the liver is an essential accessory organ of the GI tract and is the largest visceral organ in the body. It is essential for metabolism and carries out several functions including hormone production, detoxification, protein synthesis, nutrient storage specifically regulation of glycogen storage, and biochemical production. The liver can be anatomically separated into four lobes and is situated in the right upper quadrant of the abdomen.
So, now, let's look at the four lobes of the liver, and the first lobe that we will discuss is the left lobe of the liver. Seen here highlighted in green, the left lobe of the liver is situated in the left hypochondriac region and the epigastric region. Due to the position of the liver beneath the thoracic diaphragm, the superior surface of the left lobe is slightly convex. On the inferior surface of the left lobe, we can see an indentation or impression which is formed by the stomach making contact with the visceral surface of the liver. This indentation is known as the gastric impression.
The next lobe of the liver we will look at is the larger right lobe of the liver which is seen here highlighted in green. The right lobe is situated in the right upper quadrant and is separated from the left lobe of the liver via three ligaments. Anteriorly, it's separated from the left lobe by the falciform ligament, on the upper half of the posterior surface, it's separated by the venous ligament, and finally, on the lower half of the posterior surface, it's separated by the round ligament.
Now, let's look at the two smaller lobes that are visible on the inferior surface of the liver. The caudate lobe is considered part of the anatomical right lobe of the liver. As we can see in this image, the lobe is situated between the inferior vena cava, the hilum of the liver, and the venous ligament.
Next, we have the caudate process which is a small elevation of parenchyma that connects the caudate lobe and the right lobe of the liver. It is located between the lower part of the caudate lobe and the inferior surface of the right lobe superior to the hilum of the liver. We can see it here highlighted in green. The second small lobe is the quadrate lobe of the liver which is highlighted in green and is also considered to be part of the anatomical right lobe. From a functional point of view, it is part of the left lobe of the liver. As we can see in this image, the quadrate lobe is bordered by the gallbladder, the hilum of the liver, and the round ligament.
The inferior view of the right lobe presents with several impressions that are generated from the underlying organs. The first and largest one is the renal impression. The renal impression is an indentation found on the inferior aspect of the right lobe of the liver caused by the contact of the visceral surface of the liver with the right kidney. This area of the liver partially overlaps the bare area.
The second impression that can be seen on the inferior surface of the liver is the colic impression. This impression, seen here highlighted in green, is caused by the contact of the colon with the visceral surface of the right lobe. Also on the inferior surface of the right lobe of the liver adjacent to the neck of the gallbladder, we see another indentation or impression caused by the contact of the duodenum with the liver. This is known as the duodenal impression.
Now that we've covered the lobes of the liver, let's look at the ligaments that attach the liver to its position and are visible from this perspective. The coronary ligament – seen here from the inferior aspect – is one of the ligaments that attaches the liver to the inferior surface of the diaphragm. This ligament is a reflection of peritoneum that extends from the diaphragmatic to the visceral surface of the liver. It has two portions – an anterior portion and a posterior portion. On the right and left side, it continues as the right and left triangular ligament through the convergence of the anterior and posterior portions.
The area between the anterior and posterior part of the coronary ligament is called the bare area of the liver. This portion of the diaphragmatic surface of the liver is firmly attached to the inferior surface of the diaphragm by the coronary ligament. Therefore, this part of the liver is not covered by the peritoneum hence the name bare area.
The two portions of the coronary ligament that we saw earlier come together laterally to form the triangular ligaments. Immediately lateral to the left triangular ligament, we see the fibrous appendix of the liver. The next illustration shows this structure in the anterior view and, although it's not always present, it is described as a connective tissue band situated at the upper end of the left lobe of the liver. It passes along with the left triangular ligament and attaches the liver to the diaphragm.
The round ligament of the liver – also known as ligamentum teres hepatis – is a degenerative string of connective tissue that represents the remnants of the fetal umbilical vein. This ligament – as I mentioned earlier and as you can see from this anterior view – separates the left and right lobes of the liver at the posterior lower half. This ligament inserts around the umbilicus on the inner surface of the anterior abdominal wall.
Another ligament of the liver we will look at is the ligament of the inferior vena cava. This ligament – seen here highlighted in green – is a connective tissue band that forms a bridge over the inferior vena cava.
The inferior vena cava is the main vein that carries deoxygenated blood from the lower half of the body to the right atrium. It is situated in the retroperitoneal space on the posterior wall of the abdominal cavity to the right of the abdominal aorta. It runs directly behind the liver and is firmly bound to its posterior surface by the ligament that we saw previously.
The inferior vena cava receives tributaries from the common iliac veins, the lumbar veins, the right gonadal vein, the renal veins, the right suprarenal vein, the inferior phrenic vein, and the hepatic veins. It should be noted that the inferior vena cava does not drain blood from the gut. This blood has to pass through the portal vein into the liver to allow for the removal of any contaminants and for the processing of nutrients. We will see the route of this blood in the following slides.
Now, we are going to focus on a very important region of the liver which is known as the porta hepatis or the hilum of the liver. This is a fissure situated between the caudate lobe and quadrate lobe which transmits major blood and bile vessels to and from the liver as well as nerves and lymphatics. The vessels transmitted through the porta hepatis are the proper hepatic artery, the hepatic portal vein as well as the common hepatic duct which exits from here. Other structures transmitted through the porta hepatis include the hepatic branch of the vagus nerve (cranial nerve X) and sympathetic nerves.
So now let's look at some of the vessels of the liver starting with the arteries. First, we'll look at the structure seen here – the proper hepatic artery. As I mentioned earlier, one of the major vessels transmitted through the porta hepatis is the proper hepatic artery, which is one of the two terminal branches of the common hepatic artery. It runs alongside the hepatic portal vein and the common bile duct entering the liver at the hilum and forming what is known as the portal triad. So based on what I've said, the portal triad is made up of the proper hepatic artery, the hepatic portal vein and the common bile duct.
The right branch of the proper hepatic artery supplies the right lobe of the liver. It is important to note that a variation may also occur where the right hepatic artery arises from the superior mesenteric artery instead. The left branch of the proper hepatic artery supplies the left lobe of the liver. In the same way as the right branch of the proper hepatic artery, a variation may occur in the left branch where it may arise instead from the left gastric artery.
The next structure that is also part of the portal triad we looked at earlier is the hepatic portal vein. The hepatic portal vein carries nutrient-rich blood from the GI tract and the spleen to the liver. One very important point to remember is that the hepatic portal vein is not a true vein as it conducts blood to the liver and not directly to the heart. Blood from the GI tract containing both nutrients and toxins from food arise through the hepatic portal vein to the liver which is responsible for filtering it. The hepatic portal vein bifurcates into the left and right portal veins before entering the liver. The branches of the left and right portal vein are not to be confused with the left and right hepatic veins which drain into the inferior vena cava.
The hepatic portal vein forms anastomoses with the esophageal veins, the rectal venous plexus, and the superficial veins of the skin of the abdomen. From a clinical point of view, this vein is very important because every condition that causes fibrosis into the liver, for example, cirrhosis, results in an increase of blood pressure into this vein – a condition known as portal hypertension. This in turn leads to several complications such as splenomegaly, ascites, and gastrointestinal bleeding.
As I mentioned previously, the portal veins are not to be confused with the hepatic veins. The hepatic veins that we see in this vein are short intrahepatic veins that drain blood from the liver into the inferior vena cava. The right hepatic vein drains blood from the right lobe of the liver and the left hepatic vein drains blood from the left lobe of the liver and the intermediate veins drain blood from the caudate lobe. It is important to note that the hepatic veins do not contain valves.
So far, we've looked at the arteries and veins of the liver. Now, let's move on to look at the channels that collect bile from the hepatic parenchyma and transport it to the duodenum. Firstly, let's look at the right hepatic duct seen here highlighted in green. The right hepatic duct arises from the right lobe of the liver and drains bile from the right functional lobe of the liver. On the other hand, the left hepatic duct arises from the left lobe of the liver and gives off a lateral branch and a medial branch. It's effectively drains the left functional lobe of the liver. These two bile vessels we just saw – the left and right hepatic ducts – join just outside the liver parenchyma to form the common hepatic duct.
Next, let's look at the small biliary vessel seen here which drains bile from the gallbladder and that is the cystic duct. The cystic duct is a short duct into which the gallbladder opens. It contains specialized valves known as spiral valves of Heister. These valves do not provide resistance for the flow of bile and, as a result, bile can flow bidirectionally – meaning, it can flow in both directions and can be stored in the gallbladder between meals.
The cystic duct joins with the common hepatic duct that we saw previously to form the common bile duct. The common bile duct as we have seen in previous slides is formed by the union of the common hepatic duct and the cystic duct. This duct passes into the greater duodenal papilla joined by the pancreatic duct forming the ampulla of Vater that is surrounded by the sphincter of Oddi. The sphincter of Oddi helps regulate the release of bile from the gallbladder into the small intestines.
So, in this image, we can see the cystic duct and the common hepatic duct uniting to form the common bile duct highlighted in green. Normally running along with the cystic duct is a cystic artery. It arises from the right branch of the proper hepatic artery and passes to anterior and posterior surfaces of the gallbladder. This artery supplies both the gallbladder and the cystic duct.
The final structure we're going to discuss in this tutorial is a small but equally important organ that is closely associated with the liver and is known as the gallbladder. This pear-shaped organ is a reservoir for bile that's produced in the liver before it's released into the small intestines. Situated beneath the right lobe of the liver, the gallbladder measures about 8 to 12 centimeters in length. It receives bile via the common hepatic duct and the cystic duct. Bile can be stored in the gallbladder between meals as we've already discussed. During a meal, the smooth muscles in the gallbladder will contract resulting in the bile being secreted via the cystic and common bile ducts into the duodenum.
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Now, good luck everyone, and I will see you next time.