Metabolic Zonation of the Liver

The liver is the central service organ of the organism. First, the liver is the centre of metabolism: it is responsible, on the one hand, for the maintenance of the energy supply: 1. it functions as a glucostat supplying glucose when required and removing it when in excess, 2. it produces ketone bodies to feed a.o. the central nervous system, 3. it is the main site of amino acid catabolism, 4. it removes ammonia operating as a pH-stat, and 5. it processes nutrient triglycerides and fatty acids. On the other hand, the organ catalyses important biosynthetic and biodegradative processes: 1. it has a key position in the metabolism of phospholipids and cholesterol, i.e. of lipoproteins, 2. it synthesizes and probably degrades most plasma proteins, 3. it forms bile for the digestive process, and 4. it is the main organ of biochemical defense removing xenobiotics. Second, the liver is a control station of the hormonal system producing signal substances and degrading hormones during liver passage thus contributing to the maintenance of peripheral hormone levels. Third, the liver is a passive and active blood reservoir.