• The liver is derived from a foregut endodermal bud which develops in the third week of gestation and divides into two parts: hepatic and biliary.
• The Couinaud classifi cation subdivides the liver into eight segments (segments I – IV in the left lobe, segments V – VIII in the right lobe) based on vascular and biliary anatomical landmarks.
• The lobule described by Kiernan is the most widely used unit of liver microanatomy, consisting of a hexagon - like region of liver parenchyma with a central vein as its hub and portal tracts located in the periphery of the hexagon.
• Hepatocytes are functionally heterogeneous within the lobular parenchyma, whereby centrilobular cells subserve different functions (e.g. drug metabolism) from periportal cells (e.g. bile salt - dependent bile formation).
• Uncomplicated regeneration of hepatocytes and/or bile duct epithelium usually occurs by cell division of the indigenous cells; however, when normal regenerative capacity is overwhelmed there may be activation of progenitors cells located in the region of the canals of Hering.
The liver, the largest organ in the body, weighs 1200 – 1500 g and comprises one - fi ftieth of the total adult body weight. It is relatively larger in infancy, comprising one - eighteenth of the birth weight. This is mainly due to a large left lobe.
Sheltered by the ribs in the right upper quadrant, the upper border lies approximately at the level of the nipples. There are two anatomical lobes, the right being about six times the size of the left. Lesser segments of the right lobe are the caudate lobe on the posterior surface and the quadrate lobe on the inferior surface. The right and left lobes are separated anteriorly by a fold of peritoneum called the falciform ligament, posteriorly by the fissure for the ligamentum venosum and inferiorly by the fi ssure for the ligamentum teres. The liver has a double blood supply. The portal vein brings venous blood from the intestines and spleen and the hepatic artery , coming from the coeliac axis, supplies
the liver with arterial blood. These vessels enter the liver through a fissure, the porta hepatis , which lies far back on the inferior surface of the right lobe. Inside the porta, the portal vein and hepatic artery divide into branches to the right and left lobes, and the right and left hepatic bile ducts join to form the common hepatic duct. The hepatic nerve plexus contains fibres from the sympathetic
ganglia T7 – T10, which synapse in the coeliac plexus, the right and left vagi and the right phrenic nerve. It accompanies the hepatic artery and bile ducts into their finest ramifi cations, even to the portal tracts and hepatic parenchyma.
The ligamentum venosum , a slender remnant of the ductus venosus of the fetus, arises from the left branch of the portal vein and fuses with the inferior vena cava at the entrance of the left hepatic vein. The ligamentum teres , a remnant of the umbilical vein of the fetus, runs in the free edge of the falciform ligament from the umbilicus to the inferior border of the liver and joins the left branch of the portal vein. Small veins accompanying it connect the portal vein with veins around the umbilicus.
These become prominent when the portal venous system is obstructed inside the liver.
The venous drainage from the liver is into the right and left hepatic veins which emerge from the back of the liver and at once enter the inferior vena cava very near its point of entry into the right atrium.
Lymphatic vessels terminate in small groups of glands around the porta hepatis. Efferent vessels drain into glands around the coeliac axis. Some superfi cial hepatic lymphatics pass through the diaphragm in the falciform ligament and fi nally reach the mediastinal glands.
Another group accompanies the inferior vena cava into the thorax and ends in a few small glands around the intrathoracic portion of the inferior vena cava. The inferior vena cava makes a deep groove to the right of the caudate lobe about 2 cm from the midline.
The gallbladder lies in a fossa extending from the inferior border of the liver to the right end of the porta hepatis.
The liver is completely covered with peritoneum, except in three places. It comes into direct contact with the diaphragm through the bare area which lies to the right of the fossa for the inferior vena cava. The other areas without peritoneal covering are the fossae for the inferior vena cava and gallbladder.
The liver is kept in position by peritoneal ligaments and by the intra - abdominal pressure transmitted by the tone of the muscles of the abdominal wall.