The liver is the largest solid organ in the body. In adults, the liver can weigh up to 1.5 kilograms (kg). It is in the upper-right abdomen, just under the rib cage and below the diaphragm (the thin muscle below the lungs and heart that separates the chest cavity from the abdomen). The liver is part of the digestive system.

Structure

The liver has 2 main lobes: the larger right lobe and the smaller left lobe. Each lobe is divided into segments.

The lobes are separated by a band of tissue called the falciform ligament (also called the broad ligament), which helps attach the liver to the diaphragm.

A layer of connective tissue, called Glisson’s capsule or the capsule, covers the liver.

Blood vessels

Unlike most other organs, the liver has 2 major sources of blood:

• portal vein – carries blood from the digestive system to the liver
  • Approximately 75% of the liver’s blood supply comes from the portal vein.
• hepatic artery – supplies the liver with oxygen-rich blood from the heart

Most of the blood is removed from the liver through 3 hepatic veins (the right, middle and left hepatic veins) found inside the liver.

Bile ducts

The liver, gallbladder and small intestine are connected by a series of thin tubes called ducts. One function of the liver cells (hepatocytes) is to produce bile. Bile is a yellow-green fluid that helps digest fat.

Bile travels through a series of ducts in the liver to the small intestine or to the gallbladder for storage.

• Bile is collected from the liver in hepatic ducts.
• Two hepatic ducts leave the liver and join to form the common hepatic duct.
• The cystic bile duct leaves the gallbladder and joins the common hepatic duct to form the common bile duct.
• The common bile duct empties bile into the duodenum (the first part of the small intestine).
  • If there is food in the small intestine, the bile will flow directly from the liver, through the common hepatic duct and common bile duct into the duodenum to help with digestion.
  • If the small intestine is empty, the bile will collect in the common bile duct until it backs up the cystic duct and into the gallbladder, where it is stored until it is needed.

Function

The liver performs many important functions in the body. The liver:

• produces bile
  • Bile is made up of bile salts, cholesterol, bilirubin, electrolytes and water.
  • Bile helps the small intestine digest fat and absorb fats, cholesterol and some vitamins.
• absorbs and uses (metabolizes) bilirubin
  • Bilirubin is a yellow-red substance formed from hemoglobin when red blood cells (RBCs) break down. (Hemoglobin is a protein found in RBCs that carries oxygen and gives blood its red colour.)
  • The iron from the hemoglobin is stored in the liver or used by the bone marrow to produce new RBCs.
• helps the body make blood-clotting (coagulation) factors
  • The body needs bile, which is produced by the liver, to absorb vitamin K. The body uses vitamin K to produce blood-clotting factors.
  • If the liver does not produce enough bile, the body will absorb less vitamin K and produce less blood-clotting factors.
• helps the body metabolize fat
  • Bile breaks down fat from food to make it easier to digest.
• metabolizes protein
  • Liver enzymes break down proteins from food so they can be digested and used by the body.
• metabolizes carbohydrates
  • The body breaks down carbohydrates from food into glycogen, which is stored in the liver. The liver breaks down glycogen into glucose and releases it into the blood to maintain normal blood sugar levels.
• stores vitamins and minerals
  • Vitamins A, D, E, K and B12 are stored in the liver.
  • The liver stores iron in the form of ferritin, which it releases so the body can make new RBCs.
  • The liver stores and releases copper as needed.
• filters the blood
  • The liver filters certain substances from the blood so that they don’t build up and cause damage. These substances can come from within or outside the body.
    • Substances that come from within the body include hormones, such as estrogen, aldosterone and diuretic hormone.
    • Substances that come from outside the body include alcohol and other drugs, such as amphetamines, barbiturates and steroids.

Regeneration

The liver has the unique ability to regrow parts that have been removed so that it can continue to function in the body.

• Up to 80% of liver function can be maintained even after a large part of the liver has been removed.
• The regeneration process continues over several months until the missing liver tissue is replaced.
• The length of time for this process depends on the person’s age, nutrition, if there is any liver damage and how much liver was removed.