Human Liver Structure and Functions

Study Notes

The liver is the largest internal organ of the human body, weighing approximately 1.2-1.5 kg in a healthy adult.
It is divided unequally into two lobes by the ligament, with the right lobe being approximately six times larger than the left lobe.
The liver has dual blood supply through the hepatic artery (25% of liver's blood flow) and the portal vein (75%).

At the microscopic level, the liver consists of hexagonal-shaped functional units called hepatic lobules.
Hepatic lobules consist mostly of hepatocytes arranged in thin layers that radiate from the central canal to the peripheral of the lobule.
Between the radiating rows of hepatocytes are small blood vessels called sinusoids that contain specialized macrophages called Kupffer cells.
Kupffer cells act as active phagocytes capable of engulfing bacteria, debris, toxins, and other substances flowing through the sinusoids.

Stores glycogen, vitamins A, D, E, K, and B12, iron, and copper.
Produces and secretes most blood proteins, including coagulation factors (fibrinogen, prothrombin, etc.).
Removes harmful substances (e.g. ammonia and toxins) from the blood and breaks them down or transforms them into less harmful compounds.
Metabolizes most hormones and ingested drugs to rather more or less active products.
Serves as a gatekeeper between substances absorbed by the gastrointestinal tract and those released into systemic circulation.

Bilirubin is produced and metabolized in the liver.
Bile drains from hepatocytes by many small bile ducts that unite to form the main bile duct of the liver (hepatic duct).
The hepatic duct joins the cystic duct, which leads from the gallbladder, to form the common bile duct, which drains into the duodenum.