Anatomy and function

The liver is the largest organ in our body; in the healthy adult it weighs around 1200-1600g. It is located in the upper right region of the abdominal cavity (right hypochondrium), attached to the abdominal wall and diaphragm by a set of complex serous and fibroconnective ligaments.

It receives blood through two independent vascular systems: from the hepatic artery and its branches (approximately 25%) and from the portal vein with its branches (approximately 75%). Blood drainage is carried out through the suprahepatic veins (right, middle and left), tributaries of the inferior vena cava.

The microscopic unit of the liver is the hepatic lobule; a set of cells (hepatocytes) closely interconnected through a rich capillary network (sinusoids).

The product of excretion and secretion of the lobule is directed towards a third system of bile ductules, ducts, the bile duct, through which it is dumped towards the intestine.

Together the branches of the artery, vein, and bile duct form the pedicle of Glisson.

The functions of the liver are multiple and complex. They can be summarized in the following:

  • Metabolic function: the liver participates actively in the metabolism of the main substances acquired in the diet (carbohydrates, lipids, proteins and vitamins) with the aim of synthesis or storage. Many of the substances present in the blood are produced by the liver: coagulation factors, transport proteins, and acute phase proteins present during an infection. In addition, many substances of endogenous origin ("organic waste" produced by the metabolism of other organs) and exogenous (drugs, poisons, etc.) are eliminated in the liver;
  • Immune function: the liver is rich in cells of the immune system (Kupffer cells) that act as phagocytic cells capable of purifying the blood of possible circulating pathogens, especially those that come from the intestine;
  • Production and secretion of bile: the bile produced in the liver mainly fulfills two functions: a) digestion/absorption of fats and all lipophilic substances, such as some vitamins; b) means of excretion of waste substances metabolized in the liver and their elimination through the intestine.

The liver is macroscopically subdivided according to classical anatomy into lobes (right, left, quadrate, and caudate) based on lines of repair visible on its surface, determined by the insertion of the aforementioned suspensory ligaments. This subdivision into lobes does not agree with the functional subdivision of the liver, which is the basis of liver surgery today. This division is based on the portal, arterial and biliary branching (Couinaud's classification) into autonomous parenchymal regions, each one with its own Glissonian pedicle that makes an own unit: right and left liver, subdivided into 9 segments.

So, in addition to the morphological anatomy of the liver, there is also a functional anatomy that is even more important in the field of surgery.

This functional anatomy was studied by the North Americans Goldsmith and Woodburne and by the Frenchman Couinaud, and is based on the distribution of the vessels inside the liver.

The liver is then divided into two parts, the right liver and the left liver, which in turn is subdivided into segments. A segment is the smallest and independent anatomical-functional unit. Each segment receives flow both through a branch of the hepatic artery and portal vein as well as from the bile duct. These three structures are joined by connective tissue that comes from Glisson's capsule, and for this reason it is also called the Glissonian pedicle.

The blood supplying each segment is drained through a branch of the suprahepatic veins. The line that joins the left margin of the suprahepatic vein with the gallbladder is called Cantlie's line or median fissure, which corresponds to the course of the median suprahepatic vein that represents the division between the right and left liver (in anatomy it is called the limit fissure) that divides an organ into parts, which is why many call it a main fissure).

The right liver or hemiliver is divided in turn by the course of the right suprahepatic vein (right fissure) into an anterior and a posterior sector (each sector is divided into superior and inferior by a line that runs through the hepatic hilum). The right anterior sector then comprises an upper segment represented by segment VIII and a lower segment, segment V, while the right posterior sector is subdivided into segment VII above and segment VI below.

The left liver or hemiliver is also divided into two sectors, anterior and posterior, along the course of the middle suprahepatic vein (left fissure). The posterior is the largest because it comprises segments IV and III, which are divided by the falciform ligament.

The left posterior sector corresponds to segment II. Let us remember that in classical anatomy segments II and III correspond to the left hepatic lobe. Segment I or caudate lobe is the portion of parenchyma that is located anterior to the vena cava, and due to its particular vascularization it is considered an independent lobe, which is vascularized by both hemilivers. Instead, venous drainage from this lobe is directly into the vena cava through small veins called retrohepatic or Spigelian veins.