The Mammalian Liver: Structure (OCR A Level Biology)

External liver structure

• The liver is involved with the breakdown of toxic substances and the production of excretory waste; in order to carry out these roles it requires a good blood supply
  • Oxygenated blood from the heart is carried to the liver via the hepatic artery; this provides oxygen for aerobic respiration, fuelling the metabolic activity of the liver cells
  • The liver receives blood from the digestive system via the hepatic portal vein; this allows it to absorb and metabolise nutrients that are absorbed into the blood in the small intestine
  • Deoxygenated blood exits the liver in the hepatic vein and flows back to the heart
• The liver is also connected directly to the gall bladder, the role of which is to:
  • store bile, a liquid that contains:
    • bile salts for lipid digestion
    • bile pigments from the breakdown of haemoglobin
  • release bile into the duodenum via the bile duct

The liver receives oxygenated blood via the hepatic artery and nutrient-rich blood via the hepatic portal vein.

Internal liver structure

• The liver is mainly made up of cells known as hepatocytes; these cells carry out almost all the functions of the liver
• The liver cells are arranged into structures known as lobules
• Each lobule is supplied with blood by branches of the hepatic artery and the hepatic portal vein
• The blood from the hepatic artery and portal vein mixes within each lobule inside wide capillaries known as sinusoids
  • Blood within the sinusoid exchanges substances with nearby hepatocytes, allowing the hepatocytes to perform all the functions of the liver
• Each lobule is also connected to a branch of the hepatic vein that drains blood away from the lobule and into the main hepatic vein

Hepatocytes are arranged within structures known as lobules. Each lobule receives blood via branches of the hepatic artery and hepatic portal vein; this blood mixes within sinusoids.

Liver histology diagrams

Some lobule structures are visible on liver tissue micrographs