Inside the liver
The most common cells of the liver (making up roughly 90% of the liver’s cells) are called hepatocytes. They are all identical. These cells carry out most of the functions which the liver performs. The multiple tasks of the liver are not split up between them: every hepatocyte cell is capable of carrying out several functions.
Hepatocytes are split up into groups of lobules. These are the functional units of the liver. There are up to a million lobules in the liver.
Each lobule is organised around a central vein. Strips of hepatocytes radiate out from this central vein like spokes from a wheel. On the outside of each lobule are branches of both the portal vein and the hepatic artery.
Small blood channels called sinusoids run from these branches of the portal vein and hepatic artery through the lobules. There are over one billion sinusoids in the liver.
Because of this system, the blood runs very slowly through the sinusoids. This allows time for the liver cells to take in what they need from the bloodstream and to export other products.
The sinusoids are lined by tissue made up of endothelial cells. Other cells in the sinusoids include Kupffer cells, Pitt cells and Hepatic Stellate or fat cells.
Kupffer cells remove aged and damaged red blood cells, as well as attacking bacteria and viruses. Pitt cells are a type of immune cells - ‘natural killer cells’. Under certain circumstances Hepatic Stellate cells can produce collagen fibres leading to scarring or fibrosis.
Running through the lobules, alongside the sinusoids, are small channels called bile canaliculi. The bile produced by hepatocytes flows into these canaliculi and then moves to the outside of the lobule.
There it flows into branches of the bile duct which drain it into progressively larger ducts until it reaches the right and left hepatic ducts. These are the final channels out of the liver from each of its lobes.
They join up outside the liver in the common hepatic duct. This drains into the gallbladder where bile is stored until it is needed for fat digestion.
The liver also manufactures lymph which regulates the fluid balance within the body. It is a colourless fluid that flows through a network of channels called the lymphatic system.
Roughly half of the lymph made in the body is formed in the liver. It then flows through small lymphatic channels and out in the body’s main lymphatic system.
How the liver is held together
The sinusoids, lymph vessels and bile ducts are supported by connective tissue. This tissue branches out and extends throughout the liver. The tissue provides the scaffolding through which these various channels and ducts are threaded.