The liver is the only human internal organ capable of regenerating itself to a significant extent, yet it performs up to 500 separate functions that keep the body alive. This dark reddish-brown, wedge-shaped organ is the heaviest internal organ and the largest gland in the human body, weighing approximately 1.5 kilograms in men and 1.2 kilograms in women. Located in the right upper quadrant of the abdomen, it rests just below the diaphragm and is mostly shielded by the lower right rib cage. Despite its critical role, the liver is often silent until it is severely damaged, with symptoms only appearing after extensive injury has occurred. It acts as the body's chemical factory, synthesizing proteins, breaking down toxins, and regulating the metabolism of carbohydrates, fats, and amino acids. Without it, life cannot be sustained for more than a few days, as no artificial device can currently replicate its full range of capabilities.
Anatomy of a Dual Blood Supply
The liver receives its blood supply from two distinct sources, a unique arrangement that allows it to perform its complex metabolic duties. The hepatic portal vein delivers approximately 75% of the liver's blood supply, carrying nutrient-rich venous blood drained from the spleen, gastrointestinal tract, and associated organs. The hepatic arteries supply the remaining quarter, providing oxygenated blood from the aorta via the celiac trunk. These vessels subdivide into small capillaries known as liver sinusoids, which then lead to hepatic lobules. Each lobule is a hexagonal functional unit made up of millions of hepatocytes, the basic metabolic cells. The central vein of each lobule joins to the hepatic vein to carry blood out from the liver, eventually draining into the inferior vena cava. This dual blood supply ensures that the liver receives both the nutrients it needs to process and the oxygen required to power its metabolic machinery.The Silent Guardian of Metabolism
The liver is responsible for the synthesis and storage of around 100 grams of glycogen, a process known as glycogenesis, which serves as a critical energy reserve for the body. When glucose levels drop, the liver performs glycogenolysis to break down glycogen into glucose, releasing it into the blood to maintain energy homeostasis. It also performs gluconeogenesis, the synthesis of glucose from certain amino acids, lactate, or glycerol, ensuring that the brain and other vital organs have a steady supply of fuel. The liver produces bile, an alkaline fluid containing cholesterol and bile acids, which emulsifies and aids the breakdown of dietary fat. This bile is stored and concentrated in the gallbladder, a small hollow pouch that sits just under the right lobe of the liver, before being excreted to the duodenum to help with digestion. The liver also synthesizes angiotensinogen, a hormone that raises blood pressure when activated by renin, and produces insulin-like growth factor 1, which plays an important role in childhood growth and continues to have anabolic effects in adults.