The liver is an accessory organ of the gastrointestinal tract. It is a peritoneal organ, positioned in the right upper quadrant of the abdomen, and is the largest visceral structure in the abdominal cavity.
The liver performs a wide range of functions, including synthesis of bile, glycogen storage and clotting factor production. In this article, we shall discuss the anatomical position, structure, and neurovascular supply of the liver.
The liver is located in the right hypochondrium and epigastric areas, extending into the left hypochondrium.
When considering the position of the liver it is useful to consider the surfaces, ligaments and recesses that surround it.
The external surfaces of the liver can be classified by the structures they lie in close proximity to. There are two liver surfaces – the diaphragmatic and the visceral.
The diaphragmatic surface refers to the anterosuperior surface of the liver. It is smooth and convex, fitting snugly beneath the curvature of the diaphragm. A section of this surface is not covered by visceral peritoneum, known as the ‘bare area’ of the liver.
The visceral surface covers the posteroinferior aspect of the liver. It is moulded by the shape of the surrounding organs, making it irregular and flat. It lies in contact with the oesophagus, right kidney, right adrenal gland, right colic flexure, duodenum, gallbladder and the stomach.
Ligaments of the Liver
There are various ligaments that attach the liver to the surrounding structures. These are formed by a double layer of peritoneum.
Falciform ligament – attaches the anterior surface of the liver to the anterior abdominal wall. The free edge of this ligament contains the ligamentum teres, a remnant of the umbilical vein.
- Coronary ligaments (anterior and posterior folds)teac – attach the superior surface of the liver to the diaphragm.
- Triangular ligaments (left and right) – attach the superior surface of the liver to the diaphragm.
- Lesser omentum – consists of the hepatoduodenal ligament (extends from the duodenum to the liver), and the hepatogastric ligament (extends from the stomach to the liver).
In addition to these supporting ligaments, the posterior surface of the liver is secured to the inferior vena cava by hepatic veins and fibrous tissue.
The hepatic recesses are spaces between the liver and surrounding structures. They are of clinical importance, as infected fluids can collect in these areas, forming an abscess.
- Subphrenic spaces (left and right) – located between the diaphragm and liver, either side of the falciform ligament.
- Subhepatic space – located between the inferior surface of the liver and the transverse colon.
- Morison’s pouch – the posterosuperior aspect of the right subhepatic space, located between the visceral surface of the liver and the right kidney. This is the deepest part of the peritoneal cavity when supine (lying flat), and this is where fluid is likely to collect in a bedridden patient.
Structure of the Liver
The structure of the liver can be considered both macroscopically and microscopically.
The entire liver is covered by a fibrous layer, known as Glisson’s capsule. The ligaments and surface depressions of the liver divide it into four lobes.
It is divided into a right lobe and left lobe by the attachment of the falciform ligament (a fold of peritoneum that attaches the liver to the anterior abdominal wall).
There are two further ‘accessory’ lobes that arise from the right lobe, and are located on the visceral surface of liver:
- The caudate lobe is located on the upper aspect of the visceral surface. It lies between the inferior vena cava and a fossa produced by the ligamentum venosum (a remnant of the fetal ductus venosus).
- The quadrate lobe is located on the lower aspect of the visceral surface. It lies between the gallbladder and a fossa produced by the ligamentum teres (a remnant of the fetal umbilical vein).
Between the caudate and quadrate lobes is a deep fissure, known as the porta hepatis. It transmits all the vessels, nerves and ducts entering or leaving the liver with the exception of the hepatic veins.
Under the microscope, the cells of the liver (known as hepatocytes) are arranged into lobules. These are the structural units of the liver.
Each lobule is hexagonal-shaped, and is drained by a venule in its center, called a central vein. At the periphery of the hexagon are three structures collectively known as the portal triad:
- Arteriole – a branch of the hepatic artery entering the liver.
- Venule – a branch of the hepatic portal vein entering the liver.
- Duct – branch of the bile duct leaving the liver.
The portal triad also contains lymphatic vessels and vagus nerve (parasympathetic) fibres.
During embryological development, the liver is formed within part of the ventral mesentery, which suspends the foregut organs from the anterior abdominal wall. This is useful for remembering the anatomical relations of the liver:
- Superior to the liver is the diaphragm (separating the abdominal cavity from the thoracic cavity)
- Posterior to the liver are the oesophagus, stomach, gallbladder, first part of the duodenum (the foregut-derived organs).
Arterial Supply and Venous Drainage
The liver has a unique dual blood supply:
- Hepatic artery proper – supplies the liver with arterial blood. It is derived from the coeliac trunk.
- Hepatic portal vein – supplies the liver with deoxygenated blood, carrying nutrients absorbed from the small intestine. This is the dominant blood supply to the liver parenchyma and allows the liver to perform its gut-related functions, such as detoxification.
Venous drainage of the liver is achieved through three hepatic veins, which drain into the inferior vena cava.
The parenchyma of the liver is innervated by the hepatic plexus, which contains sympathetic (from the coeliac plexus) and parasympathetic (vagus nerve) nerve fibres. These fibres enter the liver at the porta hepatis and follow the course of branches of the hepatic artery and portal vein.
Glisson’s capsule, the fibrous covering of the liver, is innervated by branches of the lower intercostal nerves. Distension of the capsule results in a sharp, well localised pain.
The lymphatic vessels of the liver drain into hepatic lymph nodes. These lie along the hepatic vessels and ducts in the lesser omentum, and empty in the coelic lymph nodes.
Clinical Relevance: Percutaneous Liver Biopsy
A percutaneous liver biopsy is procedure used to obtain a sample of liver tissue. A needle is inserted through the skin to access the liver.
The biopsy is required in several clinical scenarios:
- Abnormal LFTs of unknown cause.
- Hepatitis C – Assessment for severity of liver fibrosis and disease progression.
- Other liver conditions (such as Hereditary Haemochromatosis and Autoimmune Hepatitis).
- Following liver transplantation.
During the procedure, the liver is located via ultrasound. Local anaesthetic is injected on the mid-axillary line, where on percussion there is dullness. The patient is asked to deeply expire (avoiding damage to the lungs), and the needle biopsy is taken during held expiration.
If a patient has abnormal clotting (a contraindication for the procedure), a transvenous liver biopsy can be attempted. This involves cannulating the internal jugular vein, and passing the biopsy needle through to the hepatic veins, allowing for a biopsy sample to be taken.