The liver is an organ belonging to the digestive system. It has three main functions:
- waste removal;
- and synthesis.
Functions of the liver
- Storage. The liver receives a large proportion of the blood coming directly from the digestive system. It can store nutrients from digestion and convert them into more complex molecules. It is involved in carbohydrate and lipid metabolism, and can therefore convert carbohydrates into glycogen and store it, gradually releasing glucose into the blood as the body requires. It is the only organ which both reduces and increases blood sugar. Fatty acids are also converted into complex lipid molecules (triglycerides) so that they can be stored in adipocytes (fat cells). It produces and degrades cholesterol, which is a hormone precursor and is involved in the building of cell membranes. The liver can also store fat-soluble vitamins.
- Waste removal. The liver is also the body's recycling factory. It is responsible for detoxifying the body by metabolising alcohol, drugs and medicines
- Synthesis. The liver synthesises bile. This is carried via the bile ducts to the gall bladder where it is stored. The yellow colour of bile is due to bilirubin, a degradation product of red blood cells. It is the release of bile in faeces which gives them their colour. The liver also produces many proteins, particularly those involved in blood coagulation (fibrinogen).
Structure of the liver
The liver weighs an average of 1.5 kilograms and represents 2% of body mass. It is the largest organ in the human body. It is composed of two parts, the left lobe (1/3 of its volume) and the right lobe (2/3 of its volume), separated by the falciform ligament.
The liver is highly vascularised, mostly from the hepatic artery (oxygen supply) and by the vena porta (which supplies nutrients from the intestine). Venous return is by the hepatic veins.
The liver is composed of 80% hepatocytes, and also other types of cells (bile duct cells, endothelial cells, immune cells, etc.). The liver cells are grouped into hepatic lobules that are assembled with connective tissue.
The liver is part of the digestive system and also detoxifies the body. © www-sop.inria.fr