Metabolic Functions of the Liver
Carbohydrate Metabolism
*Important in maintain blood glucose homeostasis Functions: *Coverts galactose and fructose to glucose, *Stores glucose as glycogen when blood glucose levels are high; in response to hormonal controls, performs glycogenolysis and releases glucose to blood, *Gluconeogenesis-converts amino acids and glycerol to glucose when glycogen stores are exhausted and blood glucose levels are falling, *Converts glucose to fats for storage.
Fat Metabolism
*Liver bears the major responsibility for this processes Functions: *Primary site of beta oxidation ( breakdown of fatty acids to acetyl CoA), *Converts excess acetyl CoA to ketone bodies for release to tissue cells, *Stores fat, *Forms lipoproteins for transport of fatty acids, fats, and cholesterol in blood, *Synthesizes cholesterol from acetyl CoA; catabolizes cholesterol to bile salts, which are secreted in the bile.
Biotransformation Functions
*Metabolizes alcohol and drigs by inactivating them for excretion by the kidneys, and performs reactions that may result in products which are more active, changed in activity, or less active *Processes bilirubin resulting form RBC breakdown and excretes bile pigments in bile *Metabolizes blood-borne hormones to forms that can be excreted in urine
Protein Metabolism
Functions: *Deaminates amino acids for their conversion to glucose or for the ATP synthesis; amount of deamination that occurs outside the liver is unimportant, *Forms ureas for removal of ammonia from body; inability to perform this function (e.g., in cirrhosis or hepatitis) allows ammonia to accumulate in blood, *Forms most plasma proteins, *Depletion causes rapid mitosis of hepatocytes and actual growth of liver, coupled with increased synthesis of plasma proteins until blood is normal, *Transamination-interconversion of nonessential amino acids; amount that occurs outside liver is inconsequential
Vitamin/Mineral Storage
Functions: *Stores vitamin A (1-2 yr supply), *Stores sizable amounts of vitamins D and B12 (1-4 mths suppy), *Stores iron; other than iron bound to hemoglobin, most of body's supply is stored in liver as ferritin
