Reviewed by: BD Editors

Liver Definition

The liver is a vital organ found in humans and other vertebrates. It is a large organ, with its major lobe occupying the right side of the abdomen below the diaphragm, while the narrower left lobe extends all the way across the abdomen to the left. The liver is the dark pink organ in this image:

Liver animation
(click to play animated GIF)

The liver performs many vital functions without which humans cannot survive.

Presently, there is no way to replace a liver with an artificial one in the long-term, although partial liver donations in which a donor gives part of their liver to someone in need of a transplant have been successful. The liver has a remarkable regenerative capacity, and can grow back most of its tissue if it is removed or damaged.

Despite the success of partial transplants in some cases, liver failure is an important cause of death among people with chronic alcohol and drug use.

Liver failure can also occur accidentally as a result of an accidental overdose of acetaminophen – a medicinal compound found in many over-the-counter and prescription medications. Because acetaminophen is found in so many different medications, people often don’t realize that two or more medicines they’re taking together contain the same compound, which can overwhelm the liver and lead to potentially fatal liver damage.

This is why it’s always important to tell your doctor about all medications you are taking, and check the labels of different medications for common ingredients. We will talk more about acetaminophen toxicity, and how to avoid it, below.

Liver Function

The liver serves many vital functions in the body, including:

Detoxifying the Blood

The liver’s most well-known role is as a detoxifier of the blood. It contains cells with special enzymes that can break down toxic substances into non-toxic forms.

These enzymes explain why certain medications, foods, and supplements can interact with each other. Some liver enzymes break down multiple types of toxic substances; if the enzymes are “busy” with one substance, they might not be able to break down the other substance as they usually do.

This is why you should always tell your doctor about all medications and supplements you are taking, and why some medications require that you avoid certain substances like alcohol or grapefruit.

Without these enzymes to break down toxic substances, the body slowly poisons itself. It doesn’t even need to consume anything toxic from the environment – the chemicals produced by the body’s own cells are sufficient to cause fatal toxicity over time.

Fortunately, the liver is very good at what it does. We rarely have to feel the effects of these toxins, unless we ingest large quantities of substances that can damage the liver, such as alcohol, acetaminophen, or anti-freeze.

Our livers can also run into trouble if we contract viruses that damage liver cells, such as hepatitis.

Making Blood Clotting Factors

The liver uses Vitamin K to produce proteins that are important for blood clotting. Without these proteins, the multi-step process of blood clotting may not be able to get started.

This is why people with severe liver disease or Vitamin K deficiency often develop bleeding disorders. With the body unable to clot to repair even tiny, routine injuries, people with these conditions can appear to bruise and bleed for no reason.

This can be a very serious complication in the treatment of severe liver disease, since transplantation is a surgical procedure with a risk of severe bleeding.

Making Digestive Chemicals

The liver produces bile, which is a little-known but vital ingredient to the digestive process. Bile helps the body to break down and absorb fats, and also uses it to help get rid of certain waste products.

Problems with the liver are occasionally signaled by changes in fecal matter resulting from a lack of bile in the digestive tract. That’s one reason why it’s recommended to see a doctor if you experience changes to the color, consistency, or frequency of your bowel movements that last for several weeks.

Making Energy from Protein

Under normal circumstances, the body tries not to digest proteins for energy. That’s because there are so many better uses for protein and its building blocks, such as making enzymes and other essential cellular machinery.

However, under starvation conditions where there are not sufficient stores of carbohydrates or fats to meet the body’s needs, the liver can turn amino acids into fuel for our cells to make ATP.

The liver does us a double favor here. Not only does it make it possible for our cells to survive off of proteins – it also detoxifies the toxic byproduct of this process, which is ammonia. The liver turns ammonia into urea, which can be safely eliminated by the kidneys, before releasing it into the blood.

Storing Glycogen

The liver also serves another purpose that is useful when food is scarce. It stores carbohydrates in the form of a high-density, high-calorie substance called glycogen.

Our body’s normal order of priority for digestion is: carbs, fats, protein. Our body will metabolize any carbohydrates we eat first; if it runs out of carbs, then it will turn to metabolizing our long-term fat stores.

But in between those steps, it has the liver’s glycogen. This acts as a “quick release” fuel that is easier to release and replenish than fat. Only after depleting our liver’s glycogen reserves will our body normally start digesting fat.

Breaking Down Red Blood Cells

Red blood cells die more often than any other cell type in the body. This is because red blood cells do not have nuclei, so they cannot make their own proteins. When the proteins they had at maturity wear out, they break down and are replaced by new blood cells.

Without the liver, this process would lead to severe toxicity in the blood. Dying cells release toxic compounds, which must be processed by the liver in order to keep the body safe.

Thanks to the action of the liver’s cells and enzymes, the materials from dying red blood cells are broken down into harmless forms, or even recycled for later use in new red blood cells.

Producing Hormones

The liver produces several chemical messengers that help the body to coordinate its activities. These include:

  • Insulin-like growth factor 1 – A hormone that prompts tissue to grow, and is especially important in childhood.
  • Thrombopoietin – A hormone that tells the bone marrow how many platelets to produce to help with blood clotting.
  • Hepcidin – A hormone that tells the body whether iron should be absorbed, or eliminated as waste.
  • Angiotensinogen – A pro-hormone that increases blood pressure.
  • Carrier proteins – The liver also produces carrier proteins, which bond to other hormones including sex hormones, thyroid hormone, stress hormones, and vitamins and minerals to specified destinations.

Liver Location

The liver is found within the lower ribcage, under the diaphragm which separates the heart, lungs, and stomach from the abdominal cavity.

It is located in the upper abdomen, with the bulk of the liver contained on the right side of the body. Its smaller lobe extends all the way to the left side of the diaphragm.

The liver normally cannot be felt, as it is shielded by the lower ribs. However, blows to the solar plexus – the soft part of the upper abdomen where the ribcage parts – can injure the liver.

Liver pain may appear as pain in the upper abdomen. It is usually on the left side or in the center, but can sometimes appear on the right or even seem to come from lower in the abdomen.

Doctors will often examine the abdomen if liver abnormalities are suspected, as a swollen liver can often be felt despite the ribcage.

Acetaminophen Toxicity

Some medicinal compounds are considered so safe and effective that they are used in dozens of different medications. Acetaminophen is one of these. The main ingredient in Tylenol, it relieves pain and reduces fever with a very good safety profile – as long as you take it in the correct doses.

Unfortunately, because acetaminophen is so effective, it is found in many, many medications. One of the most common causes of liver damage in the U.S. is people taking two or more of these medications at once, not realizing that they all contain the same ingredient. This can result in an overdose, especially if multiple medications containing acetaminophen are taken over long periods of time.

Acetaminophen is processed by the liver into a toxic product, which can poison the liver. In the proper doses, the liver can eliminate this byproduct without any problem, but when people take more acetaminophen than they should over a period of days or weeks, the product can build up and kill liver tissue.

This is unfortunately common since acetaminophen is included in some medications which are advertised to treat joint pain, fever, heartburn, flu symptoms, cough, menstrual cramps, and more. People often don’t think that these medications are related or that they might contain the same ingredients.

When taking multiple medications on the same day, it is a good idea to check the labels for shared ingredients. Taking a proper dose of acetaminophen is safe and effective – but taking two or three times the proper dose can cause very big problems.

Medications which contain acetaminophen and should not be taken together include:

Actifed Alka-Seltzer Plus Anacin
Bitartrate Butalbital Cepacol
Contac Coricidin Dayquil
Dimetapp Dristan Endocet
Excedrin Fioricet Feverall
Formula 44 Goody’s Powders Hycotab
Hydrocet Liquiprin Lortab
Midol MIDRIN Mucinex
NORCO Nyquil Oxycodone
Panadol Percocet Phenaphen
Robitussin ROXICET Saint Joseph Aspirin-Free
Sedapap Singlet Sinutab
Sudafed Tapanol Tramadol
Triaminic Tylenol Brand Products Tylox
Ultracet Vanquish Vicodin
Vicks Zydone


1. Which of the following is NOT a function of the liver?
A. Breaking down toxins into harmless substances
B. Breaking down old red blood cells
C. Metabolizing glucose for the body
D. Storing carbohydrates

Answer to Question #1
C is correct. The liver metabolizes protein when it is needed for fuel – not glucose. All cells are capable of metabolizing glucose for energy, while protein metabolism requires the liver because it produces toxic byproducts.

2. Which of the following is NOT a common cause of liver failure?
A. Chronic, heavy alcohol consumption
B. Viral hepatitis
C. Too much exercise
D. Acetaminophen toxicity

Answer to Question #2
C is correct. A, B, and D are common causes of liver failure.

3. Pain in which of the following areas might originate with the liver?
A. Right upper quadrant of the abdomen
B. Central upper quadrant of the abdomen
C. Right upper quadrant or lower abdomen
D. All of the above

Answer to Question #3
D is correct. While the liver is primarily located in the right and central upper parts of the abdomen, the path of nerves in the abdomen can sometimes cause liver pain to manifest on the left side, or even in the lower abdomen.


  • Boron, W. F., & Boulpaep, E. L. (2009). Medical physiology: a cellular and molecular approach. Philadelphia, PA: Saunders/Elsevier.
  • Common Medicines With Acetaminophen. (n.d.). Retrieved July 11, 2017, from
  • Acetaminophen Toxicity. (2017, January 06). Retrieved July 11, 2017, from
  • Hoffman, M. (n.d.). Picture of the Liver. Retrieved July 11, 2017, from
  • How does the liver work? (2016, August 22). Retrieved July 11, 2017, from

Cite This Article

MLAAPAChicago Editors. "Liver." Biology Dictionary,, 26 Jul. 2017, Editors. (2017, July 26). Liver. Retrieved from Editors. "Liver." Biology Dictionary., July 26, 2017.

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