Liver is the largest gland of the body and is very versatile in functions it performs. It is classified as an accessory organ of the gastrointestinal tract and is an important component of the digestive system.
Location of liver:
Liver occupies the upper part of the abdominal cavity just beneath the diaphragm. Its greater part is situated under cover of the right costal margin. The right hemidiaphragm separates it from the pleura, lungs, pericardium and heart.
From the right side, the liver extends to the left to reach the left hemidiaphragm. The convex upper surface of liver is molded to the undersurface of domes of both halves of diaphragm. For this reason, the liver is rather irregular in shape.
Porta hepatis is the hilum of the liver where different structures enter or exit. It is located on the posteroinferior surface of the organ. For detailed description, visit Porta Hepatis.
Structure of liver:
Liver is a soft and pliable organ. It may be divided into a large right lobe and a small left lobe by the attachment of the falciform ligament. The larger right lobe, in addition to its native portion, is further divided into a quadrate lobe and caudate lobe by the presence of the gallbladder, the fissure of the ligamentum teres, the inferior vena cava, and the fissure for the ligamentum venosum.
Experiments have shown that although the quadrate and caudate lobes lie adjacent to the right lobe, they are functional parts of the left lobe of the liver. This is further elaborated by the fact that the right hepatic ducts are distributed only to the right lobe while the left hepatic ducts are distributed to the left lobe as well as caudate and quadrate lobes.
Relations of liver:
- Right and left costal margins
- Right and left pleura and lower margins of both lungs
- Xiphoid process
- Anterior abdominal wall
- Right kidney
- Hepatic flexure of the colon
- Gall bladder
- Inferior vena cava
- Fundus of stomach
Peritoneal ligaments of liver:
The liver is covered by visceral peritoneum, which on certain places is folded upon itself to form the peritoneal ligaments. These ligaments do not have any function to perform and are in no way related to the ligaments of joints. The peritoneal ligaments of liver include:
- Falciform ligament
- Ligamentum teres
- Ligamentum venosum
- Lesser omentum
For detailed description, visit the page: Peritoneal ligaments of liver.
Bile ducts of liver:
Liver secretes bile at a constant rate of about 40mL per hour. During most of the time, when digestion is not taking place, the bile is stored and concentrated in the gall bladder. Later, when required , it is delivered to the duodenum through the bile ducts.
The bile ducts of the liver consists of the following:
Vascular system of the liver:
Liver is made up of lobules, each of which has a central vein that is a tributary of the hepatic veins. In the spaces between adjacent liver lobules are the portal canals, which contain branches of the hepatic artery, portal vein and a tributary of a bile duct, forming the portal triad.
The arterial and venous blood passes between the liver cells by means of sinusoids and drains into the central vein.
Blood supply of liver:
Arterial blood supply to the liver comes from the hepatic artery, which is a branch of the celiac artery. The former divides into right and left terminal branches and enter the porta hepatis.
In contrast to other organs of body, the liver is related to two types of veins. One of these, the portal vein, forms the hepatic portal system and the other, the hepatic vein, is just like all other veins draining the venous blood from the organ.
The portal vein divides into right and left terminal branches that enter the porta hepatis behind the corresponding branches of hepatic artery.
The hepatic veins, which may be three or more in number, emerge from the posterior surface of the liver and drain into the inferior vena cava.
Basic pattern of blood circulation:
The hepatic artery brings about 30% of liver’s blood supply, the remaining 70% being brought by the portal vein. The blood brought by these two sources differs in characteristics. The hepatic artery brings oxygenated blood while the portal vein brings deoxygenated venous blood. Unlike blood in other veins, the blood of the portal vein is rich in nutrients (products of digestion), which are absorbed from the gastrointestinal tract.
After both portal vein and hepatic artery enter the liver, the arterial and venous blood is conducted to the central vein of each liver lobule by liver sinusoids. The central vein drains into the right and left hepatic veins, which leave the posterior surface of the liver to drain into the inferior vena cava.
Nerve supply to liver:
Sympathetic and parasympathetic nerves reach the liver from the celiac plexus. In addition, the anterior vagal trunk gives rise to a large hepatic branch, which passes directly to the liver.
Lymph drainage of liver:
Liver produces huge quantities of lymph, about one third to one half of all body lymph. In response to this, the lymphatic system of the liver is very sophisticated. The lymph vessels leave the liver and enter several lymph nodes in the porta hepatis. The efferent vessels from these nodes pass to the celiac nodes and join the lymph coming from other regions of body.
A few lymph vessels pass from the bare area of the liver through the diaphragm to the posterior mediastinal lymph nodes.
Basic functions of liver:
The liver performs three basic functions, as described below.
- The first function is production and secretion of bile, which is passed into the intestinal tract or stored in the gall bladder.
- The second function is its involvement in many metabolic activities related to the metabolism of carbohydrates, fats and proteins.
- The third function is filtration of blood, whereby it removes bacteria and other foreign particles that have gained entrance into the blood from the gastrointestinal tract.
In addition to the above basic function, another important function of liver is production of heparin, an anticoagulant substance. The liver also has an important detoxicating function.