The liver, located in the upper right abdomen, performs many roles, supporting metabolism, immunity, digestion, and detoxification. Its fundamental operational units are microscopic structures known as liver lobules. These units are responsible for carrying out the liver’s extensive functions, processing blood and performing various metabolic activities.
Understanding the Liver Lobule’s Structure
A classical liver lobule is hexagonal, with a central vein at its core. At each of its six corners, a “portal triad” contains a branch of the hepatic artery, a branch of the hepatic portal vein, and a small bile duct.
Hepatocytes, the liver cells, radiate outwards from the central vein in plates. Between these plates are sinusoids, specialized capillaries with a discontinuous lining allowing direct blood-hepatocyte contact. Kupffer cells, macrophages within the sinusoids, ingest worn-out blood cells, pathogens, and debris. Adjacent to hepatocytes are bile canaliculi, tiny channels where bile is secreted.
Key Functions Within the Liver Lobule
Hepatocytes within the liver lobule carry out many metabolic activities. They are responsible for detoxification, processing substances like drugs, alcohol, and waste products from the blood. This detoxification process helps remove harmful compounds from the body before they can cause damage.
The lobule plays a significant role in nutrient metabolism. Hepatocytes process carbohydrates by storing glucose as glycogen and converting it back to glucose when the body needs energy. They also engage in the metabolism of fats and proteins, including the synthesis of plasma proteins, such as albumin and clotting factors. Furthermore, the liver lobule stores fat-soluble vitamins, including vitamins A, D, E, and K, and reuses iron from old red blood cells. Bile, produced by hepatocytes, is another important secretion that aids in the digestion and absorption of lipids in the small intestine.
How Blood and Bile Move Through the Lobule
Blood enters the liver lobule through the portal triads. Oxygenated blood arrives via branches of the hepatic artery, while nutrient-rich, deoxygenated blood from the digestive tract enters through branches of the hepatic portal vein. These two blood supplies mix within the sinusoids, flowing past the hepatocytes.
As blood moves through the sinusoids, the hepatocytes absorb nutrients and other substances, while Kupffer cells remove waste and pathogens. This processed blood then converges into the central vein located at the lobule’s core. From the central vein, blood eventually drains into larger hepatic veins, which then empty into the inferior vena cava, returning blood to the heart.
In contrast, bile produced by hepatocytes flows in the opposite direction to blood. Bile is secreted into tiny channels called bile canaliculi, which are formed by the membranes of adjacent hepatocytes. These canaliculi radiate outwards from the center of the lobule, collecting bile and draining into small bile ductules within the portal triads.
These ductules then merge to form larger bile ducts, which transport bile out of the liver towards the duodenum for digestion or to the gallbladder for storage.