Right upper quadrant of the abdomen

Liver

The liver occupies the upper part of the abdominal cavity just beneath the diaphragm. Its convex superior surface is molded to the under surface of the domes of the diaphragm muscle, and it extends from the right fifth intercostal space down to the right costal margin. Grossly, the liver is divided into right, left, caudate, and quadrate lobes due to peritoneal and ligamentous attachment. The larger right and smaller left lobes are demarcated by the falciform ligament. The quadrate lobe exists between the gallbladder and round ligament. In turn, inferior vena cava, ligamentum venosum, and porta hepatis make the boundaries of caudate lobe.

The porta hepatis, or hilus of the liver, is a deep fissure in the inferior surface of the organ. It contains the hepatic ducts and branches of the portal vein and hepatic artery. The circulatory system of the liver is unlike that seen in any other organ. Roughly 75% of the blood entering the liver is venous blood from the portal vein, while the remaining 25% of the blood supply to the liver is arterial blood from the hepatic artery. Within the liver, the portal vein divides into right and left branches and then further into smaller channels (clinical fun fact: these smaller channels help define the liver segments used in surgical resections). On the other hand the hepatic arterial tree, that is often a branch of the celiac trunk, terminates in two plexuses: peribiliary plexus, which supports the functions of the biliary epithelium of the bile ducts and the periportal plexus that supplies the portal canals and drains into periportal sinusoids.

Recall that the liver microanatomy is based on the concept of the liver lobule. The liver lobule is a hexagonal prism of liver tissue with a central vein and six portal canals located at the angles of the hexagon. Sinusoids are the largest microvascular circulation of the liver, conducting nutrients, hormone-rich portal venous blood, and highly oxygenated arterial blood slowly past the liver cells, i.e. hepatocytes. The sinusoids of the liver drain directly into the central veins, which are the smallest branches of the efferent vasculature (blood leaving the liver to return to the heart). The central veins coalesce to form large right, middle and left hepatic veins, which empty into the inferior vena cava, just beneath the right atrium of the heart.

The liver performs multiple functions which can be summarised as

• clearance of toxins, bacteria and bilirubin
• storage of glycogen, vitamin and essential elements
• metabolism of carbohydrates, amino acids and lipids
• synthesis of albumin, clotting factor and anticoagulants

Gallbladder

It is present underneath the right lobe of the liver and consists of the neck, body, and fundus. It collects, concentrates, and secretes bile salts from the liver into the duodenum. The liver synthesizes bile salts and refluxes them into the gallbladder through the cystic duct. The stimulation of the gallbladder leads to its contraction and bile salts are secreted into the duodenum via the cystic duct into the common bile duct. These bile salts help to emulsify fats into globules that can be digested chemically.