Liver

The liver is an organ in vertebrates, including humans. It plays a major role in metabolism and has a number of functions in the body including detoxification, glycogen storage and plasma protein synthesis. It also produces bile, which is important for digestion. Medical terms related to the liver often start in hepato- or hepatic from the Greek word for liver, hepar.

Anatomy

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Human liver, view from above

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View from below

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The adult human liver normally weighs between 1.0 - 2.5 kilograms, and is a soft, reddish-brown "wedge-shaped" organ. It is the largest organ in the abdomen and sits immediately under the diaphragm on the right side of the upper abdomen. The liver lies anterior to the gallbladder and superior to the right kidney.

Related Topics:
Kilogram - Abdomen - Diaphragm - Anterior - Gallbladder - Kidney

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The liver is supplied by two major blood vessels: the hepatic artery and the portal vein. The hepatic artery normally comes off the celiac trunk. The portal vein brings venous blood from the digestive tract, so that the liver can process the nutrients and toxic byproducts of food digestion. The hepatic veins drain directly into the inferior vena cava.

Related Topics:
Hepatic artery - Portal vein - Celiac trunk - Hepatic vein - Inferior vena cava

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The bile produced in the liver is collected in bile capillaries which merge to form bile ducts. These eventually drain into the right and left hepatic ducts, which in turn merge to form the common hepatic duct. The cystic duct (from the gallbladder) joins with the common hepatic duct to form the common bile duct. Bile can either drain directly into the duodenum via the common bile duct or be temporarily stored in the gallbladder via the cystic duct. The common bile duct and the pancreatic duct enter the duodenum together at the Ampulla of Vater. The branchings of the bile ducts resemble those of a tree, and indeed the term "biliary tree" is commonly used in this setting.

Related Topics:
Bile - Duodenum - Gallbladder - Ampulla of Vater

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It is unique as the only internal human organ capable of natural regeneration of lost tissue; as little as 25% of remaining liver can regenerate into a whole liver again.

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Surface anatomy

Apart from a patch where it connects to the diaphragm, the liver is covered entirely by visceral peritoneum, a thin, double-layered membrane that reduces friction against other organs. The peritoneum folds back on itself to form the falciform ligament and the right and left triangular ligaments. These "ligaments" are in no way related to the true anatomic ligaments in joints, and have essentially no functional importance, but they are easily recognizable surface landmarks. Traditional gross anatomy divided the liver into four lobes based on surface features.

Related Topics:
Diaphragm - Peritoneum

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The falciform ligament is visible on the front (anterior side) of the liver. This divides the liver into a left anatomical lobe, and a right anatomical lobe.

Related Topics:
Falciform ligament - Anterior

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If the liver is flipped over, to look at it from behind (the visceral surface), there are two additional lobes between the right and left. These are the caudate lobe (the more superior), and below this the quadrate lobe.

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From behind, the lobes are divided up by the ligamentum venosum and ligamentum teres (anything left of these is the left lobe), the transverse fissure (or porta hepatis) divides the caudate from the quadrate lobe, and the right sagittal fossa, which the inferior vena cava runs over, separates these two lobes from the right lobe.

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Functional anatomy

For purposes such as advanced liver surgery, it is crucial to understand the organization of liver based on blood supply and biliary drainage. The central area where the common bile duct, portal vein, and hepatic artery enter the liver is the hilum or "porta hepatis". The duct, vein, and artery divide into left and right branches, and the portions of the liver supplied by these branches constitute the functional left and right lobes. The functional lobes are separated by a plane joining the gallbladder fossa to the inferior vena cava. In the widely used Couinaud or "French" system, the functional lobes are further divided into a total of eight segments based on secondary and tertiary branching of the blood supply. The segments corresponding to the surface anatomical lobes are as follows:

Related Topics:
Common bile duct - Portal vein - Hepatic artery

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Fetal blood supply

In the growing fetus, a major source of blood to the liver is the umbilical vein which supplies nutrients to the growing fetus. The umbilical vein enters the abdomen at the umbilicus, and passes upward along the free margin of the falciform ligament of the liver to the inferior surface of the liver. There it joins with the left branch of the portal vein. The ductus venosus carries blood from the left portal vein to the left hepatic vein and thence to the inferior vena cava, allowing placental blood to bypass the liver.

Related Topics:
Umbilical vein - Falciform ligament - Ductus venosus - Inferior vena cava

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After birth, the umbilical vein and ductus venosus are completely obliterated two to five days postpartum; the former becomes the ligamentum teres and the latter becomes the ligamentum venosum. In the disease state of cirrhosis and portal hypertension, the umbilical vein can open up again.

Related Topics:
Ligamentum teres - Ligamentum venosum - Cirrhosis - Portal hypertension

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