Anatomy and Function of the Liver

The liver is a large, meaty organ that sits on the right side of the belly. The liver has two large sections, called the right and the left lobes.

• The liver is an essential organ that has many functions in the body, including making proteins and blood clotting factors, manufacturing triglycerides and cholesterol, glycogen synthesis, and bile production.
• The liver is a large organ that sits on the right-hand side of the belly.
• The liver is the body's largest internal organ.
• Many different disease processes can occur in the liver, including infections such as hepatitis, cirrhosis (scarring), cancers, and damage by medications or toxins.
• Symptoms of liver disease can include
  • jaundice,
  • abdominal pain and swelling,
  • confusion,
  • bleeding,
  • fatigue, and
  • weight loss.
• Alcohol can be toxic to the liver (hepatotoxic), especially in high doses, and long-term alcohol abuse is a common cause of liver disease.
• The liver is involved in metabolizing many toxins, including drugs and medications, chemicals, and natural substances.

The liver's main job is to filter the blood coming from the digestive tract, before passing it to the rest of the body.

The liver has multiple functions. It makes many of the chemicals required by the body to function normally, it breaks down and detoxifies substances in the body, and it also acts as a storage unit.

Hepatocytes (hepar=liver + cyte=cell) are responsible for making many of the proteins (protein synthesis) in the body that are required for many functions, including blood clotting factors, and albumin, required to maintain fluid within the circulation system. The liver is also responsible for manufacturing cholesterol and triglycerides. Carbohydrates are also produced in the liver and the organ is responsible for turning glucose into glycogen that can be stored both in the liver and in the muscle cells. The liver also makes bile that helps with food digestion.

The liver plays an important role in detoxifying the body by converting ammonia, a byproduct of metabolism in the body, into urea that is excreted in the urine by the kidneys. The liver also breaks down medications and drugs, including alcohol, and is responsible for breaking down insulin and other hormones in the body.

The liver is also stores vitamins and chemicals that the body requires as building blocks. These includes:

• vitamin B12,
• folic acid,
• iron required to make red blood cells,
• vitamin A for vision,
• vitamin D for calcium absorption, and
• vitamin K to help the blood to clot properly.

Is the liver a gland or an organ?

The liver is one of the vital organs of the body, responsible for hundreds of chemical actions that the body needs to survive. It is also a gland because it secretes chemicals that are used by other parts of the body. For these reasons the liver is both an organ and a gland; in fact, it is the largest internal organ in the body.

The liver is a large organ and a significant amount of liver tissue needs to be damaged before a person experiences symptoms of disease. Symptoms also may depend upon the type of liver disease.

• The inflammation of hepatitis may be associated with pain in the right upper quadrant of the abdomen, nausea and vomiting. This may also be seen in people with gallstones.
• People may have jaundice (have a yellow-orange hue to their skin) because the liver cannot metabolize bilirubin (the normal breakdown product of old red blood cells).
• There may be a tendency to bleed excessively or bruise easily because the liver is unable to manufacture blood clotting factors in adequate amounts.
• Fatigue, weakness, weight loss, and shortness of breath because of muscle wasting; due to the inability of the liver to manufacture proteins.
• Because the liver is involved in the metabolism of sex hormones, gynecomastia (enlarged breast tissue in men) and impotence may occur.
• In end-stage liver disease, ascites (fluid accumulation in the abdominal cavity), and leg swelling may occur because of inadequate production of albumin by the liver.
• There also may be difficulty in metabolizing ammonia causing its levels in the blood to rise, resulting in confusion due to encephalopathy (encephala=brain + pathy=dysfunction).

The liver is the largest internal organ of the body and is located in the right upper quadrant of the abdomen, beneath the diaphragm and is protected by the lower right ribs.

The liver is divided into two lobes and has a rich blood supply obtained from two sources: 

1. the portal vein delivers blood from the gastrointestinal tract (stomach, intestine, colon) and spleen, and
2. the hepatic artery supplies blood from the heart.

The biliary tree describes a system of tubes that collect bile, used to help digest food, and drains it into the gallbladder or the intestine. Intrahepatic ducts are located inside the liver (intra=inside + hepar=liver) while extrahepatic ducts are located outside the liver.

Many diseases may affect the liver directly or as a consequence of an illness or disease that begins in another organ.

Fatty liver disease

• Fatty liver disease, caused by accumulation of cholesterol and triglycerides within the liver is not associated with alcohol abuse. Fatty liver disease is also referred to as nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH).

Cirrhosis

• Cirrhosis of the liver describes a condition of scarring in the liver that is not reversible and may lead to liver failure.
• Alcohol abuse causes cirrhosis of the liver and is the most common cause of liver disease in North America.

Hepatitis

Hepatitis is an infection of the liver that causes liver inflammation.

• Hepatitis A is often spread by poor sanitary habits including poor handwashing and may be transmitted by food handlers. It tends to be self-limited.
• Hepatitis B and hepatitis C are spread by contact with infected body fluids.
• Hepatitis D is spread in conjunction with hepatitis B and needs the B virus for it to survive in the body and cause liver damage.
• Hepatitis E is a food or water borne infection.
• There are vaccinations available to prevent hepatitis A and hepatitis B.

Infections

Infections may affect the liver, including:

• Epstein Barr virus that causes infectious mononucleosis
• Adenovirus
• Cytomegalovirus
• Toxoplasmosis
• Rocky Mountain spotted fever

Medications or drug-induced liver inflammation

Liver inflammation is a relatively common side effect of medications. Some commonly prescribed medications include the following:

• acetaminophen over the counter (Tylenol, Panadol) but also in prescription pain medications (hydrocodone/acetaminophen (Lortab, Vicodin, Norco)
• Statins (medications used to control elevated blood cholesterol levels)
• Antibiotics (amoxicillin-clavulanic acid [Augmentin, Augmentin XR], nitrofurantoin [Macrodantin, Furadantin, Macrobid], tetracycline, isoniazid)
• methotrexate (Trexall, Rheumatrex)
• disulfiram (Antabuse)
• Herbal remedies, for example, kava kava, mahuang, comfrey

Toxins

• Poisonous mushrooms may damage the liver and cause liver failure.
• Alcohol in large doses can be toxic for the liver and damages the liver over time.
• Aflatoxins produced by certain fungi are toxic to the liver
• Industrial chemicals may be toxins that affect the liver, such as arsenic and carbon tetrachloride

Genetic disorders

Genetic disorders can affect the liver, examples include the following:

• Hemochromatosis with abnormal iron storage
• Wilson's Disease with abnormal copper storage
• Gilbert's Disease with abnormal bilirubin metabolism

Cancer

• Primary liver cancers arise directly from cells within the liver.
• Metastatic liver disease describes cancer that arises from another organ and invades the liver

Abnormalities of bile flow from the liver

Abnormalities of bile flow from the liver may lead to liver inflammation, for example:

• Gallstones (the most common disease)
• Primary biliary cirrhosis
• Primary sclerosing cholangitis.

Decrease in blood flow draining from the liver

Decrease in blood flow draining out of the liver may cause the liver to become congested and inflamed, two examples include:

• Congestive heart failure (CHF) is a condition in which the heart is not strong enough to pump all of the blood it receives, and that blood can back up into the liver.
• Budd Chiari syndrome is a disease in which blood clots form in the hepatic veins, preventing blood from leaving the liver.

The liver is located in the abdomen but the health care professional will want to examine the whole body to look for the consequences of liver disease.

• The abdomen may be palpated to feel for an enlarged liver. As it grows, the liver edge may be felt below the right rib margin. An inflamed liver in acute hepatitis may be tender but a liver that is cirrhotic, small and shrunken, may not be able to be felt.
• If liver disease is a consideration, the health care professional also may feel for an enlarged spleen and assess whether excess fluid is present in the abdomen (ascites), perhaps indicating the presence of portal hypertension.
• The skin, including the sclera of the eyes, may be assessed for color looking for jaundice. Spider nevi, or angiomata, are a collection of blood vessels under the skin and may be normal, but in the proper setting may indicate liver disease.
• If the person is confused (hepatic encephalopathy), the doctor may attempt to illicit asterixis, or flap on the physical examination. These people may not be able to keep their wrists cocked when their arms are held outstretched but instead see their wrists rhythmically flapping.
• Blood tests may be ordered to help make the diagnosis. Liver enzymes levels may reveal liver inflammation. However, in patients with end-stage liver disease, the liver can burn itself out and the enzymes may be normal even in the face of severe disease. Other blood tests that may be appropriate include a complete blood cell count (CBC), hepatitis virus screen, and blood clotting tests (a sensitive way to measure function since the liver is responsible for manufacturing the proteins involved in the blood clotting mechanism).
• On occasion, ultrasound may be helpful in assessing the anatomy of the liver and this may lead to other tests including CT scan to further assess the anatomy and structure of the liver and surrounding tissues.

Most often, diseases of the liver can be diagnosed by history, physical examination, and blood tests. On occasion, should the diagnosis be unclear or to assess the degree of damage to the liver, a liver biopsy may be necessary.

Using a very thin needle, a gastroenterologist or hepatologist (two types of liver specialists) or an interventional radiologist will insert a very fine needle through the skin and into the liver, to retrieve a small bit of tissue. This can then be examined under the microscope by a pathologist to help make the diagnosis. This procedure is done under sterile conditions to prevent infection, and a local anesthetic is injected into the skin to decrease the potential for pain.

If there is concern about only one area of the liver, instead of a disease that would affect the whole organ, an ultrasound may be used to help guide the needle into the proper position.

• Moderate alcohol consumption to decrease the risk of the most common cause of liver disease in North America.
• The risk of contracting hepatitis B and hepatitis C can be decreased by minimizing exposure to body fluids.
• As mentioned previously, vaccinations are available for hepatitis A and B.
• Maintain a healthy weight and eat a balanced diet to decrease the risk of developing fatty liver disease.

• Diseases of the liver may be treated by primary care or internal medicine specialists.
• Gastroenterologists are specialists that focus on the digestive organs and liver.
• A hepatologist is a specialist focused exclusively on the liver.
• Depending upon the exact type of liver disease, other specialists may be involved in the care of patients with liver disease, including infectious disease specialists, surgeons, oncologists, critical care specialists, hematologists, and emergency medicine specialists.