The liver possesses extraordinary metabolic diversity, performing hundreds of different chemical reactions to accomplish a broad array of functions that support the human body. Among the most important of the many functions of the liver are its roles in glucose and protein metabolism, and drug and chemical detoxification. Impairments of these functions in people with severe liver disease often cause serious, potentially life-threatening medical problems.
Glucose Metabolism
The liver plays a principal role in maintaining glucose balance in the body. In response to glucose-regulating hormones, the liver stores or releases glucose as needed by the body. As blood sugar levels increase after a meal, the liver takes up excess glucose and stores it as the chemical glycogen. When the body requires glucose between meals, the liver reverses the glucose storage process, transforming glycogen into glucose for release into the bloodstream. If glycogen stores are exhausted, the liver manufactures glucose from other non-sugar chemicals, explains biochemist Michael W. King, Ph.D., in the electronic reference materials published by The Medical Biochemistry Page.
Protein Metabolism
The liver conducts much of the breakdown, processing and production of body proteins and protein building blocks, or amino acids. The liver receives amino acids absorbed by the bloodstream from the digestion of dietary proteins. The amino acids are either broken down into smaller chemicals to be used in the production of energy, recirculated or utilized in the production of needed body proteins, explains the medical reference text "Harrison's Principles of Internal Medicine."
The liver produces many types of proteins, including albumin, globulins, fat-transporting proteins and an array of proteins called clotting factors that work together to halt bleeding. Severe liver damage may critically impair the protein-producing capacity of the organ, causing widespread metabolic disturbances in the body.
Drug and Toxin Metabolism and Detoxification
The liver possesses a variety of mechanisms to deactivate, detoxify and eliminate drugs and toxins from the body. A diverse group of liver enzymes called the cytochrome P450 system interacts with drugs, changing the chemical structure of the drug as it passes through the liver, as explained on the University of Nottingham School of Nursing, Midwifery and Physiotherapy educational website.
In most cases, the drug-enzyme interaction in the liver deactivates the drug. Less commonly, liver metabolism is required to activate a drug into a therapeutic form. In addition to deactivation, drug metabolism in the liver typically alters medications such that they can be eliminated through the urine or bile. Toxins, including alcohol, are metabolized by the liver using many of the same mechanisms utilized for drug deactivation and elimination.
Patients with severe liver disease often have a limited capacity to metabolize medications. The dosages of medications that undergo liver metabolism must be decreased to accommodate for the diminished rate of drug deactivation and elimination.
References
- The Medical Biochemistry Page: Gluconeogenesis
- "Harrison’s Principles of Internal Medicine, 16th Edition"; Dennis L. Kasper, M.D., et al., Editors; 2004
- Colorado State University Hypertexts for Biomedical Sciences: Metabolic Functions of the Liver
- The University of Nottingham School of Nursing, Midwifery and Physiotherapy: The Liver and Drug Metabolism
- University of Maryland Medical Center: Liver Disease, The Liver
