The liver is the largest organ in the body, normally weighing about 1.5kg (although this can increase to over 10kg in chronic cirrhosis). The liver is the main organ of metabolism and energy production; its other main functions include:
· Bile production
· Storage of iron, vitamins and trace elements
· conversion of waste products for excretion by the kidneys
The liver is functionally divided into two lobes, right and left. The external division is marked on the front of the liver by the falciform ligament, which joins the coronary ligament at the superior margin of the liver.
· The right lobe is separated from the other lobes by the gallbladder fossa and the fossa for the inferior vena cava on the visceral surface of the liver.
· The left lobe includes the caudate and quadrate lobes. It is separated from these two lobes by the attachment of the ligumentum teres, and the fissures for the ligumentum teres and the ligamentum venosum.
· The caudate lobe lies between the fissure for the ligamentum venosum and the fossa for the inferior vena cava.
· The quadrate lobe is partly covered by the gallbladder in normal patients; anatomically, it lies between the fissure for the ligamentum teres and the gallbladder fossa.
Each lobe hs its own arterial and venous supply and its own billiary drainage. all the lobes perform the same functions- there are no areas of specialisation.
The Portal Circulation
The liver is unusual in that it has a double blood supply; the right and left hepatic arteries carry oxygenated blood to the liver, and the portal vein carries venous blood from the GI tract to the liver.
The venous blood from the GI tract drains into the superior and inferior mesenteric veins; these two vessels are then joined by the splenic vein just posterior to the neck of the pancreas to form the portal vein. This then splits to form the right and left branches, each supplying about half of the liver.
On entering the liver, the blood drains into the hepatic sinusoids, where it is screened by specialised macrophages (Kupffer cells) to remove any pathogens that manage to get past the GI defences. The plasma is filtered through the endothelial lining of the sinusoids and bathes the hepatocytes; these cells contain vast numbers of enzymes capable of braking down and metabolising most of what has been absorbed.
The portal venous blood contains all of the products of digestion absorbed from the GI tract, so all useful and non-useful products are processed in the liver before being either released back into the hepatic veins which join the inferior vena cava just inferior to the diaphragm, or stored in the liver for later use.
Surface Markings of the Liver
When examining a patient, it is important to recognise where the internal organs lie relative to the surface anatomy you can see. The liver can essentially be visualised as a triangle, with its upper margin below the nipples on either side of the chest, and the lower margin making a line from just above the tenth rib on the right side to below the nipple on the left side. The superior surface of the liver lies just below the diaphragm; this means that the lower margin of the liver will move downwards on inspiration, and this can be palpated. As the liver is also a very dense organ, it is very dull to percussion and you can easily percuss out the borders of the liver if palpation is unsuccessful.
The gallbladder area can be palpated around the tip of the right ninth rib. The normal gallbladder is impalpable; it only becomes palpable when distended with stones or bile, and the area will become very tender if there is inflammation present.