Inside the liver—the body's refinery

Nutrition Health Review, Fall, 2002 by Gail Gorman

The liver is the largest gland in the human body. Located behind the lower ribs on the right side of the abdomen, in healthy adults it weighs about 3 pounds and is roughly the size of a football. At any moment in time, it holds about 13% of the total blood supply, and yet we still do not fully understand all that this organ does for us or exactly how it does it. More than 500 functions have been identified to date, for example:

* Filtering and refining ingested substances

* Storing iron and certain vitamins, minerals, and sugars

* Removing bacteria from the bloodstream

* Neutralizing and destroying poisonous substances, such as converting ammonia to urea

* Maintaining hormonal balance and blood glucose levels

* Regulating transport of chemicals and nutrients used by the body for energy

* Controlling blood clotting

* Managing production and excretion of cholesterol

* Serving as the main organ of blood formation before birth

* Regenerating its own damaged tissue (the liver is the only organ to do so)

* Producing bile, which enables the digestion of fats

The liver is soft and solid in consistency, dark reddish-brown, and indispensable to life. It is uniquely positioned between the intestines and the heart in such a way that all blood, thick with nutrients, bacteria, and potential toxins from the digestive process, passes through the liver before being sent to the heart for general circulation.

Here, in our chemical processing plant, everything we eat (except for long-chain fatty acids) is processed into the essential chemicals of life. Toxins are removed and converted so that they can be eliminated. Bile is produced to be stored in the gallbladder for use later in processing fats and fat-soluble vitamins (A, D, E, and K).

Internally, the liver has more than 100,000 hepatic lobules, each of which is a small six-sided structure composed of cells (hepatocytes) packed in slabs.

Eighty-five to ninety percent of all blood that leaves the stomach and intestines carries ingested substances directly to the liver, where macrophages (Greek for "big eaters") or Kupffer cells remove large amounts of debris and bacteria. In the liver, drugs are chemically modified, thus defining the system's reaction to them.

Liver Diseases

Because the liver is our body's central refinery, it is affected by ingested chemicals whether they are prescription drugs, street drugs, or an over-the-counter product. In fact, almost every known pharmaceutical has, at one time or another, been implicated as a cause of liver damage. Every drug, industrial solvent, and pollutant, whether inhaled or swallowed, presents a challenge to our metabolism, sometimes resulting in damage to the liver.

Chemicals that damage the liver fall into two groups: predictable toxins and unpredictable ones. Predictable liver toxins regularly cause damage after exposure of a certain strength or duration in a large percentage of the population.

Unpredictable toxins cause damage in only a small percentage of the general public or in people with existing liver disease. Unpredictable damage appears to result from an allergic reaction that targets liver cells. A surprisingly large number of prescription drugs that are considered safe and currently in general use have been shown to cause significant liver damage in some people.

Predictable damage seems to be the result of ingestion of certain chemicals, specifically those that are difficult for the kidneys to excrete. The liver tries to clean up the blood by modifying those chemicals. During the process, other more dangerous toxins are formed and they then attack the liver and damage the cells. Injury can range from destruction of a few cells, which the liver can usually replace, to sudden and acute liver failure that calls for immediate hospitalization and eventual liver transplantation. Examples of known predictable liver toxins are the cleaning solvent carbon tetrachloride and the pain killer acetaminophen.

Acetaminophen is present in many over-the-counter and prescription drugs (e.g., Tylenol[R], Nyquil[R], Excedrin[R]) and is safe for most people when taken as prescribed. When it is taken in excess or over a long period of time, however, serious liver damage is the predictable result. Acetaminophen is toxic at lower doses in individuals who regularly consume more than two drinks a day or in those who may experience an allergic reaction.

Excessive exposure to certain other chemicals, in particular synthetic hormones or steroids, can result in a tumor, an abnormal mass of tissue that forms when cells begin to reproduce at an uncontrolled rate. Of course, the liver can be invaded by both noncancerous (benign) and cancerous tumors; in fact, benign tumors are quite common and usually produce no symptoms.

There are several types of benign tumors, including hepatocellular adenoma, which occurs most often in women of childbearing age and is associated primarily with the use of oral contraceptives, and hemangioma, a mass of abnormal blood vessels. Up to 5 percent of adults are believed to have small liver hemangiomas that are asymptomatic and require no treatment. Cancerous tumors are discussed later.