Liver diseases and conditions
This article is the continuation of a previous article on liver.
The liver is a vital organ with over 500 functions, each one of which could malperform. As it supports almost every other organ in the body, its illnesses are never localized, but rather have a widespread effect. In addition, these effects can manifest in a myriad of ways precisely due to its widespread reach and involvement, making the diagnostics complicated.
A filter and a barrier
As the liver is both a filter and a barrier from the abdominal to the thoratic cavity, it is suceptible to infections. Moreover, one of its primary goals is to filter the blood in search for bacteria and viruses. Usually the immune system neutralizes any threat detected, however, a large enough wave of infectuous material can cause hepatitis.
Hepatitis is the inflammation of the liver, and the most usual cause is viral. Named after this condition is a family of viruses, hepatitis A, B, C, D and E (some of which are sexually transmissive). Chronic infection with hepatitis B and C is the main cause of liver cancer, with 248 million people globally having chronic hepatitis B infection, and 142 million having chronic hepatitis C infection. Other usual suspects of hepatitis are from a family of Herpesviridae, such as the herpes simplex virus. Hepatitis A and E viruses seldom cause chronic inflammations, while hepatitis D can only infect a cell in the presence of hepatitis B.
Extreme hepatitis can cause hepatic encephalopathy, an accumulation of toxins in the bloodstream usually removed by the liver. This condition is the final stage of liver failure, and can be fatal, or result in a coma.
Liver tumors, while usually suspected to come from a viral infection, can also be attributed to a variety of internal and external factors. Genetic predisposition always plays a role in formation of tumors, but is not the only intrinsic factor. Hormones and especially growth factors can accelerate, and even ignite tumorogenesis as well.
External factors can range from exposure to radiation and chemicals, to smoking, nutrient imbalance, alcoholism and overall bad lifestyle – all have a profound impact on the formation of liver tumors. Liver is especially succeptible to external stimuli as it is both a blood funnel and a sieve, and the only tissue in the adult human that can reasonably and on a continual basis regenerate itself. So no matter where the toxin comes from – inhaling tobacco smoke, drinking heavy liquors or eating processed food – it will end up in the liver. And chances are, one of those regenerating cells will have its DNA altered into a tumorous cell.
Excessive alcohol consumption diseases are grouped under the term alcoholic liver disease, and include alcoholic hepatitis, fatty liver and cirrhosis.
Many diseases of the liver are accompanied by jaundice caused by increased levels of bilirubin in the system. The bilirubin results from the breakup of the hemoglobin of dead red blood cells; normally, the liver removes bilirubin from the blood and excretes it through bile, but a damaged liver, or otherwise occupied with hepatitis, is not able to fulfill that role.
Such is the case in alcoholic hepatitis, where the patients also experience hepatomegaly (enlargement of liver tissue), ascites (fluid retention in the abdominal cavity) and fatigue.
Fatty liver, also known as hepatic steatosis is usually the first step in alcoholic hepatitis, where fatty cells replace, or are introduced besides the functioning cells of the liver. It is accompanied by mild symptoms, the most prominent being mild hepatomegaly.
Cirrhosis is the end result of a liver mistreatment or illness, with the liver functions being impaired due to scar tissue formation where regenerated cells should be. Such fibrous tissue replaces normal, functioning liver tissue over time, rapidly rendering the liver useless.
Picture 1: Micrograph showing cirrhosis with trichrome staining. By Nephron, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=7844681.
The most common cause of cirrhosis in the Western world is alcohol abuse - the cause of cirrhosis in this case.
Besides these, there are many other, less prevalent hepatic diseases. And as is the case with most conditions, the best treatment is prevention. To keep the liver functional and useful for many years, it is important to know how it functions. With that knowledge, we can avoid excessive smoking, drinking and any drug abuse, as well as eat a diet with balanced nutrients.
To determine the well being of a liver, a doctor will usually perform a liver function test, also called a hepatic panel. It is a group of blood tests specifically aimed at liver enzymes and byproducts.
Bilirubin is the byproduct of heme, a hemoglobin precursor responsible for oxygen distribution. The liver is responsible for its clearance, and any value above 17 μmol/L indicates liver disease. When total bilirubin levels exceed 40 μmol/L, bilirubin deposits at the sclera, skin, and mucous membranes will give these areas a yellow colour, also called jaundice.
ALT is short for alanine transaminase, enzyme found in the muscle energy cycles (specifically the Cahill and Cori cycles). Any kind of liver injury will cause elevated ALT. However, lower ALT elevations (up to 300 IU/L) might indicate problems with other organs, such as kidneys or heart, whereas higher ALT values are tied to liver damage, reduced insulin response, reduced glucose tolerance, and increased free fatty acids and triglycerides.
AST, aspartate transaminase, is paired with ALT in liver tests due to it being almost exclusively found in the liver, while AST is found in the liver, heart (cardiac muscle), skeletal muscle, kidneys, brain, and red blood cells. As a result, ALT is a more specific indicator of liver inflammation than AST, as AST may be elevated also in diseases affecting other organs.
Ongoing search for diagnostic tools
Scientists are always on the lookout for better, easier, non-invasive methods of disease detection, and for liver that would mean tests that could be done without drawing blood. For example, a test that could determine the well being of a liver from urine or saliva would both diminish its cost and the discomfort (and potential complications) some patients might have with drawing blood. Several tests are in the testing phase, ranging from skin patch diagnostics to organ imaging, but they will yet have to see wide application.
- Evaluating intrinsic and non-intrinsic cancer risk factors. Song Wu, Wei Zhu, Patricia Thompson and Yusuf A Hannun. NATURE COMMUNICATIONS| (2018) 9:3490 |DOI: 10.1038/s41467-018-05467-z|www.nature.com/naturecommunications
- Mengel, Mark B.; Schwiebert, L. Peter (2005). Family medicine: ambulatory care & prevention. McGraw-Hill Professional. p. 268. ISBN 978-0-07-142322-9.
- Lisa B, VanWagner (3 February 2015). "Evaluating Elevated Bilirubin Levels in Asymptomatic Adults". Journal of the American Medical Association. 313 (5): 516–517. doi:10.1001/jama.2014.12835. PMC 4424929. PMID 25647209.
- Abdel-Misih, Sherif R.Z.; Bloomston, Mark (2010). "Liver Anatomy". Surgical Clinics of North America. 90 (4): 643–653.
- Zakim, David; Boyer, Thomas D. (2002). Hepatology: A Textbook of Liver Disease (4th ed.). ISBN 9780721690513.
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