The liver is central to health, providing numerous synthetic, metabolic, bioactivating, conjugating, and elimination functions (see table) that are essential to normal homeostasis. It orchestrates synthesis and metabolism of lipids, carbohydrates, and proteins; storage, metabolism, and activation of certain vitamins; and storage of minerals, glycogen, and triglycerides. It provides coagulant, anticoagulant, and essential acute phase proteins and can function as an on-demand site of extramedullary hematopoiesis.
Summary of Major Hepatobiliary Functions
Category | Biochemical | Hepatobiliary Functions |
|---|---|---|
Carbohydrate metabolism | Glucose | Homeostasis, gluconeogenesis, glycogenolysis |
Insulin | Metabolism, degradation | |
Glucagon | Metabolism, degradation | |
Glycogen | Metabolism, storage | |
Growth hormone | Regulation | |
Lipid metabolism | Cholesterol | Synthesis, esterification, excretion |
Bile acid | Synthesis, regulation | |
Ketogenesis, fatty acid | Oxidation, mobilization | |
Triglycerides | Metabolism, storage | |
Lipoprotein | Synthesis, release | |
Phospholipid | Metabolism | |
Protein metabolism | Albumin | Synthesis, turnover (endocytosis by sinusoidal endothelium) |
Globulins: acute phase proteins, transport proteins, certain immunoglobulins (bile) | Synthesis, turnover | |
Apoproteins | Synthesis (some) | |
Coagulation proteins: Procoagulants Activators Inhibitors | Synthesis Procoagulants, inhibitors Procoagulants, inhibitors | |
Amino acid | Synthesis, regulation | |
Ammonia | Synthesis, detoxification | |
Urea | Synthesis | |
Vitamin metabolism | Water-soluble vitamins: B1, B6 (pyridoxine), B12 (cyanocobalamin), folic acid, nicotinic acid, riboflavin | Activation, synthesis, storage |
Fat-soluble vitamins: E, D, A, and K | Activation, synthesis, storage | |
Other micronutrients (eg, zinc, copper, iron) | Storage, metabolism | |
Immunologic functions | Kuppfer cells Sinusoidal endothelium | Population, function, phagocytic protection, gut bacteria, toxins particulate debris Complement metabolism, interleukin production Immunomodulation (metabolic products) IgA production and biliary excretion |
Endocrine hormone metabolism | Polypeptide hormones | Target organ influence, hormone degradation |
Steroid hormones | Conjugation, degradation/excretion | |
Hematologic functions | Blood cellular components | In utero hematopoiesis (in fetal liver), blood storage, intrahepatic extramedullary hematopoiesis (in severe anemia), senescent RBC breakdown |
Coagulation system components | Factor, inhibitor, synthesis, activation, overall homeostasis | |
Hematopoietic factors (B12, folate, iron) | Storage/activation | |
Reticuloendothelial system | Transferrin | Synthesis |
Iron | Homeostasis, storage | |
Bilirubin | Uptake, conjugation, excretion, enterohepatic circulation | |
Digestive functions | Bile acids | Synthesis, regulation, optimization of fat digestion, enterohepatic circulation |
Bile | Synthesis, excretion | |
Gallbladder | Bile storage, bile release synchronization with meals | |
Detoxication and excretory functions | Bilirubin | Conjugation, uptake, biliary excretion |
Ammonia | Urea cycle | |
Steroid hormones | Cortisol, androgen, estrogen, aldosterone | |
Xenobiotics | Barbiturates, chloramphenicol, clindamycin, metronidazole, propranolol, theophylline, propoxyphene, pentazocine, diazepam, meperidine, lidocaine, aminophylline | |
Copper | Cytosolic storage proteins, lysosomal storage, canalicular elimination | |
Cholesterol | Biliary excretion | |
Enterohepatic circulation | Bile acids | Essential for homeostasis |
Nutrients | Essential to many nutrients | |
Xenobiotic metabolites (drugs, toxins) | Involved in biometabolism |
The liver also contributes to digestion via synthesis and enterohepatic circulation of bile acids and influences the enteric biome (bile acids and IgA in bile) and systemic immunologic responses. It is central to the metabolism of endogenous and exogenous compounds, including a variety of xenobiotics, drugs, and toxins via bioactivation, biotransformation, detoxification, and elimination.
Housing the largest population of fixed macrophages in the body (Kupffer cells), the liver also orchestrates clearance of bloodborne toxicants, particulate and soluble debris, and bacteria and their toxins, many derived from the digestive canal.
