Abdomen:Solid viscus:Liver

The **liver** plays a major role in metabolism and has a number of functions, including glycogen storage, decomposition of red blood cells, plasma protein synthesis, hormone production, and detoxification. It is an irregular, wedge-shaped organ, weighing 1500g, that lies below the diaphragm in right hypochondrium and epigastrium and is in close approximation with the stomach and the gallbladder. It is largely covered by the costal cartilages.

The liver is almost entirely covered by visceral peritoneum and is associated with a number of peritoneal ligaments including the falciform ligament. The posterocranial aspect of the liver, adjacent to the dorsal body wall, is not completely covered by peritoneum, resulting in a "bare area".

The liver is described as having two surfaces, diaphragmatic and visceral, sharply demarcated anteriorly by the inferior margin:

* diaphragmatic surface: smooth convex peritoneal area that faces superiorly and anteriorly to the diaphragm and includes the bare area. It is descriptively divided into anterior, superior, posterior and right surfaces without well-defined boundaries.
* visceral surface: faces inferiorly and posteriorly and is covered by peritoneum and in contact with the visceral organs and lies the porta hepatis. It has several impressions made by the stomach, duodenum, hepatic flexure, right kidney, IVC, gallbladder.

The liver usually measures:

* craniocaudal length: 10-12.5 cm
* transverse diameter: 20-23 cm

Lobes: the liver has four lobes, divided by the attachment of the falciform ligament and fissures for ligamentum teres/venosum, the IVC and gallbladder.

- right lobe: right of the falciform

- left lobe: left of the falciform

- caudate lobe: between IVC and ligamentum venosum

- quadrate lobe: between gallbadder fossa and ligamentum teres.

Ligaments:

- falciform ligament: peritoneal reflection on to the anterior body wall and the diaphragm. The lower free edge houses the ligamentum teres. The ligament passes ascend on the anterior surface to the superior surface where it split into right and left leafs. The right leaf is the upper coronary ligament (passing in front of the IVC), and left leaf is the left triangular ligament.

- lesser omentum: double visceral peritoneum that pass from the the oesophagus, lesser curvature of the stomach and the 1st part of duodenum to the fissure of the ligamentum venosum. The layers opens at the porta hepatis to enclose the content, including right and left hepatic ducts and branches of the hepatic artery and portal vein.

- coronary ligament: peritoneal reflections right of the lesser omentum, from the posterior surface of the liver onto the inferior aspect of diaphragm. It has an upper and lower layer. The upper layer is continuous with the right leaf of the falciform ligament, and lower layer is continuous with the right leaf of the lesser omentum. At the apex of convergence, is the right triangular ligament.

- triangular ligament: reflection of the peritoneum from the liver to the diaphragm. Has left and right ligament.

**Bare area:** area of the liver not covered by peritoneum, right of the IVC. It is bounded by the IVC, upper layer of coronary ligament and lower layer of coronary ligament.

- it is in contact with the diaphragm and the right suprarenal gland.

The posterior and inferior aspect of the liver forms a H-shaped arrangement of structures. The IVC and gallbladder, at the center forms the right limb of H. The fissures of the ligamentum venosum and ligamentum teres forms the left limb of H. Between the IVC and the ligamentum venosum is the caudate lobe. Due to the depth of the fissure, the caudate lobe is partly separated from the rest of the liver.

The **porta hepatis**, lies in the middle of the H, on the visceral surface. It houses of the inflow and outflow tract to the liver in the order VAD (vein, artery duct) with the duct most anteriorly. it contains hepatic artery, portal vein and common bile duct, and other lymph nodes and nerves to the liver.

Arterial supply

* The liver receives a dual blood supply from the portal vein and hepatic arteries. The hepatic portal vein supplies ~75% of the liver's blood supply by volume and carries venous blood drained from the spleen, gastrointestinal tract, and its associated organs.
* The hepatic arteries supply arterial blood to the liver and account for the remainder of its blood flow. The hepatic arterial system supplies the biliary system. In the liver, it divides into left and right branches and then medial and lateral sectoral branches. The common hepatic artery, right hepatic can arise from the SMA, or the left hepatic from the left gastric artery.
* Compression of the portal vein and hepatic artery below the porta hepatis significantly reduce the inflow of blood and useful in trauma.
* Oxygen is provided from both sources; approximately half of the liver's oxygen demand is met by the hepatic portal vein, and half is met by the hepatic arteries.

Venous drainage

While the arterial supply does not demonstrate mixing, the venous return shows extensive mixing between left and right halves of the liver. There are three hepatic veins draining into the IVC. All the veins have no extrahepatic course and enters the IVC below the central tendon of the diaphragm.

Lymph drainage:

Drain into three or four **hepatic nodes** at the porta hepatis. They receive lymphatics from the gallbladder too. These pass to coeliac nodes.

Lymphatics from the bare area communicate through the diaphragm with posterior mediastinal lymph nodes.

Nerve supply

The liver is supplied by sympathetic and parasympathetic fibres from the hepatic nerve plexus, which travel with branches of the hepatic artery and portal vein to the liver. Within the liver the nerve fibres accompany the portal triad. Sympathetic fibres are derived from the coeliac plexus and parasympathetic fibres are derived from the anterior and posterior vagal trunks.

Variant anatomy

* lobar variation
	+ Riedel lobe
	+ agenesis of the right hepatic lobe
	+ agenesis of the left hepatic lobe
	+ accessory hepatic lobes / ectopic liver tissue
	+ supradiaphragmatic liver
* pseudolipoma of the Glisson capsule
* accessory hepatic sulci
* SMA origin of hepatic artery