The liver is the largest gland and second largest organ after the skin. It is a peritoneal organ located under the diaphragm in the upper quadrant of the abdomen and extends to the left upper abdomen.
The liver is involved in many functions including synthesis of bile, glycogen storage, and clotting factor production.
Hepar is the Latin term for liver and its word derivatives like hepato, hepatic are often used in medical literature to denote origin from the liver.
In fact, interestingly, the heparin, an anticoagulant is named so because it was first derived from dog liver.
The liver weighs around 1600 grams in males and 1300 grams in females.
Liver Anatomy Details
The liver is predominantly located in the right hypochondrium and epigastric areas and extends into the left hypochondrium.
External anatomy can be studied better by considering it in the form of surfaces, borders, ligaments and the anatomical spaces (recesses) that surround it.
External Surfaces of Liver
There are five surfaces of the liver – anterior, posterior, superior, inferior and right.
Out of these, the inferior surface is well defined and is demarcated anteriorly by a sharp inferior border.
The other surfaces are almost continuous with each other with separation not very clear between them.
[Anterosuperior surfaces are together termed as the diaphragmatic surface of the liver and the posteroinferior as visceral surface.]
The diaphragmatic surface is smooth and convex and nicely fits under the curvature of the diaphragm. It is formed by anterior and superior surfaces.
The posterior aspect of the diaphragmatic surface is not covered by visceral peritoneum and is called the bare area of the liver. It is separated from the diaphragm by loose connective tissue.
The upper surface of the liver is percussed at the level of the fifth intercostal space.
The anterior surface is separated from the inferior (visceral) surface by a sharp anterior (inferior) border. This border can be palpated clinically on deep inspiration.
The visceral surface is the posteroinferior surface of the liver. It is mostly covered with peritoneum except for the fossa of the gallbladder and porta hepatis.
The porta hepatis is a transverse fissure about 5 cm, on the undersurface of the liver with the quadrate lobe in front and the caudate lobe behind. It contains the common hepatic duct, the proper hepatic artery, and the portal vein, enclosed in the hepatoduodenal ligament which is formed by two layers of the lesser omentum.
It is irregular and flat in shape, molded by the shape of the surrounding organs.
The surface is related to the hepatic flexure, right kidney, transverse colon, duodenum, and stomach. The hepatic flexure is the area where the vertical ascending (right) colon takes a right-angle turn to become the horizontal transverse colon.
An H-shaped fissure marks the Inferior surface of the liver.
- The right vertical arm of the H – Formed by the gallbladder anteriorly and the inferior vena cava (IVC) posteriorly. There is a caudate process between the two.
- The left vertical arm of the H is formed by the ligamentum teres hepatis in front and the ligamentum venosum behind.
- The transverse limb of the H is the porta hepatis (hilum).
Ligaments of the Liver
The various ligaments that attach the liver to the surrounding structures are formed by a double layer of peritoneum.
Most of the liver is covered by peritoneum except
- Bare area
- Groove for inferior vena cava
- Fossa for gall bladder
- Porta hepatis
All the ligaments of the liver are actually peritoneal folds.
The falciform ligament
The falciform ligament divides the liver into a larger anatomical right lobe and a smaller anatomical left lobe. It attaches the anterosuperior surface of the liver to the anterior abdominal wall and diaphragm.
The free edge of the falciform ligament contains the ligamentum teres hepatis or round ligament of the liver which is remnant of the umbilical vein.
The coronary ligament has anterior and posterior folds and represents reflections of the visceral peritoneum covering the superio-posterior surface of the liver onto the diaphragm. It attaches the superior surface of the liver to the inferior surface of the diaphragm and demarcates the bare area of the liver.
The anterior and posterior folds unite to form the triangular ligaments on the right and left lobes of the liver.
The bare area lies between two leaves of the coronary ligament to the right of the inferior vena cava.
The falciform ligament is continuous with the anterior layer of the coronary ligament.
The posterior layer of the coronary ligament on the right side is called the hepatorenal ligament.
On the left, the anterior and posterior layers of the coronary ligament unite to form the left triangular ligament. On the right, the anterior and posterior layers of the coronary ligament unite to form the right triangular ligament.
The hepatorenal pouch is the area below the posterior layer of the right triangular and coronary ligament over the right kidney.
There are two triangular ligaments – left and right.
The left triangular ligament is formed by the union of the anterior and posterior layers of the coronary ligament at the apex of the liver and attaches the left lobe of the liver to the diaphragm.
The right triangular ligament is formed in a similar fashion adjacent to the bare area and attaches the right lobe of the liver to the diaphragm.
Lesser omentum attaches the liver to the lesser curvature of the stomach and first part of the duodenum as hepatoduodenal ligament and the hepatogastric ligament.
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.
- Inferior vena cava ligament is a bridge of tissue between posterior surface of right lobe and caudate lobe behind the inferior vena cava.
Hepatic recesses are anatomical spaces between the liver and surrounding structures.
- Subphrenic spaces
- Located between the diaphragm and the anterior and superior aspects of the liver.
- Divided into right and left by the falciform ligament.
- Subhepatic space
- It is a peritoneal space located between the inferior surface of the liver and the transverse colon.
- Morison’s pouch
- Present between the visceral surface of the liver and the right kidney. This is the deepest part of the peritoneal cavity.
Gross Structure of the Liver
The liver is covered by a fibrous layer, known as Glisson’s capsule.
Anatomically, the liver is divided into a larger right lobe and a smaller left lobe by the falciform ligament.
[This division of lobes is not very useful and therefore surgical liver anatomy is also discussed later.]
In addition to these two lobes, there are two accessory lobes that arise from the right lobe, and are located on the visceral surface of the liver. These are known as caudate and quadrate lobes.
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. Ligamentum venosum is the remnant of the fetal ductus venosus, which in fetal life shunts a portion of umbilical vein to the inferior vena cava.
The quadrate lobe is located on the lower aspect of the visceral surface between the gallbladder and a fossa produced by the ligamentum teres.
A deep, transverse fissure – known as the porta hepatis or the hilum separates these two accessory lobes. It transmits all the vessels, nerves and ducts entering or leaving the liver with the exception of the hepatic veins.
The left lobe forms nearly one-sixth of the liver. Its inferior surface presents an elevation called omental tuberosity.
The liver has a unique dual blood supply from the hepatic artery and portal vein.
It takes about 20-40% of the blood supply to the liver and supplies the non-parenchymal structures of the liver with arterial blood.
The common hepatic artery is derived from the coeliac artery and runs toward the right on the superior border of the proximal body of the pancreas.
It gives two branches – gastroduodenal artery and right gastric artery, it continues as the hepatic artery proper in the free edge of the lesser omentum. In porta hepatis, it divides into the right and left hepatic artery.
Hepatic portal vein is responsible for 60-80% of blood supply. It comes from the gut with partially deoxygenated blood and nutrients absorbed from the small intestine. This is the dominant blood supply to the liver parenchyma.
It also allows the liver to perform its gut-related functions, such as detoxification.
The portal vein is formed by the union of the superior mesenteric vein and the splenic vein behind the neck of the pancreas. It collects blood from the gastrointestinal tract, the spleen, and the pancreas. It then ascends in the hepatoduodenal ligaments behind the common bile duct and the proper hepatic artery.
At the porta hepatis or hilum into right and left portal vein branches in the hepatic hilum.
Hepatic veins are responsible for venous drainage of the liver.
The central veins collect the blood from each hepatic lobule and form collecting veins which then combine to form three hepatic veins namely right hepatic, middle hepatic and left hepatic vein. These three veins are largely intrahepatic and lie on the posterior surface of the liver.
These hepatic veins then open into the inferior vena cava.
The middle and the left hepatic vein may join to form a common trunk before draining into the vena cava.
As we know, the inferior vena cava also lies on the posterior surface of the liver in a groove between the bare area on the right, the caudate lobe on the left, and the caudate process in front.
Nerve Supply of Liver
The liver parenchyma is supplied via the hepatic plexus. Hepatic plexus is formed by sympathetic (coeliac plexus) and parasympathetic (vagus nerve) nerve fibers. The fibers enter the liver at the hilum [porta hepatis] and follow the course of branches of the hepatic artery and portal vein.
Glisson’s capsule is innervated by branches of the lower intercostal nerves.
Hepatic lymph nodes lie along the hepatic vessels and ducts in the lesser omentum and receive lymphatic vessels of the anterior aspect of the liver. Hepatic lymph nodes further drain into the colic lymph nodes which in turn, drain into the cisterna chyli.
Lymphatics from the posterior aspect of the liver drain into phrenic and posterior mediastinal nodes. These further drain to the right lymphatic and thoracic ducts.
Surgical Anatomy of Liver
The traditional morphological anatomy is based on the external appearance of the liver and does not show the internal features of vessels and biliary ducts branching. Therefore the traditional morphological description of the liver is not useful during surgery of the liver.
The surgical anatomy or functional anatomy was described by Couinaud.
Couinaud divided the liver into a functional left and right liver by a main portal scissurae or intersegmental plane that lies along the middle hepatic vein. This is known as Cantlie’s line and externally runs from the middle of the gallbladder fossa anteriorly to the inferior vena cava posteriorly.
The right and left lobes of almost equal (60:40) in size.
Each lobe is further divided into sectors by scissurae containing right and left hepatic veins, respectively.
- The right porta scissura containing the right hepatic vein separates the right hemiliver into anterior and posterior sectors.
- The left hemiliver is divided into a lateral section (segments 2 and 3) and a medial section (segment 4) by the line between the falciform ligament and the umbilical fissure.
[Couninaud originally divided the left hemiliver into anterior and posterior sectors along portal scissura containing the left hepatic vein.]
The liver is divided into eight functionally independent segments. Each segment has its own vascular supply, venous drainage, and biliary drainage. In the center of each segment there is a branch of the portal vein, hepatic artery, and bile duct. In the periphery of each segment, there is vascular outflow through the hepatic veins.
[Note: Brisbane 2000 Terminology, the sectors are termed as sections. Both the terms are used]
The numbering of the segments is in a clockwise manner.
Segment 1 is what is traditionally known as the caudate lobe and is located posteriorly. It is not visible on a frontal view. Segments 2-4 are present in left hemiliver and 5-8 in right hemiliver.
As we see in the adjoining images, distribution of segments is as follows
- Segment 1 is Caudate lobe
- Segment 2,3 form the left lateral sector
- Segment 4 forms the left medial sector
- Segment 4 is the quadrate lobe
- May divide into superior (4a) and inferior subsegments (4b)
- Segments 5, 8 form the right anterior sector
- 8–superior, 5-inferior
- 6,7 right posterior sector
- 7-superior, 6-inferior
Thus segments 1,6 and 7 are posterior and not visible from the frontal side. The right border of the liver is formed by segments 5 and 8.
Although segment 4 is part of the left hemiliver, it is situated more to the right.
Right and left portal vein branches divide the right and left lobes of the liver into superior and inferior halves.
The superior half of the liver is composed of (from right to left) segments 7,8, 4a and 2.
The inferior half is composed of (from right to left) segments 6, 5, 4b and 3.
The right portal vein divides the posterior sector of the right lobe into segments 7 (superior) and 6 (inferior) and the anterior sector of the right lobe into segments 8 (superior) and 5 (inferior).
The left portal vein divides the medial sector of the left lobe (sector 4 or quadrate lobe) into subsegments – a (superior) and b (inferior) and the lateral sector of the left lobe into segments II (superior) and III (inferior).
This superior and inferior division of the segments can be very well seen in Computed Tomography (CT scan).
The left and right portal veins branches superiorly and inferiorly to project into the center of each segment.
Microscopic Anatomy of Liver
Microscopically, the cells of the liver or hepatocytes are arranged into lobules. Lobules form the structural units of the liver.
Each anatomical lobule is hexagonal-shaped and is drained by 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
- Venule – a branch of the hepatic portal vein
- Bile duct – a branch of the bile duct
The portal triad also contains lymphatic vessels and vagus nerve (parasympathetic) fibers.
Functions of Liver
More than 500 vital functions have been attributed to the liver. The important and more common are given below
- Synthesis of bile
- Helps to digest fats in the small intestine
- Also carries excretory function
- Synthesis of important plasma proteins
- Production of cholesterol and special proteins to help carry fats in the body
- Converts surplus glucose to glycogen for storage which could be used when required.
- Regulates blood levels of amino acids
- Processes hemoglobin and stores its iron content
- Detoxifies ammonia
- Metabolizes and excretes many drugs
- Synthesis and regulation of clotting factors
- Produces immunoglobins and complement system for the immune system
- Clearing the blood of drugs and other poisonous substances
- Clearance of bilirubin