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about the liver

Your liver is for life. You have only one and though it is unique in its ability to regenerate, it can only survive limited damage – so it does need looking after.

Place your right hand over the area under your ribs on the right side of your body and it will just about cover the area of the liver. The liver is the largest gland, and solid organ in the body, weighing some 1.8 kgs in a men and 1.3 kgs in women. It holds approximately 13% (about one pint or 0.57 litres) of the total blood supply at any given moment, and it has over 500 estimated functions.

Position of the liver in the body      Image of the liver

Position of the liver in the body


The liver is dark reddish brown in colour and is divided into two main lobes (the much larger right and the smaller left), which are further subdivided into approximately 100,000 lobules. About 60% of the liver is made up of liver cells (hepatocytes), and each of these have an average lifespan of 150 days. In every milligram of liver tissue there are approximately 202,000 cells. Two-thirds of the body of the liver is the parenchyma, which contains the hepatocytes, and the remainder is the biliary tract. The liver receives its blood supply via the hepatic artery and portal vein (which transports nutrients from the intestine (gut)).

 The Biliary System
The Liver and Biliary Tract

The biliary tract contains the right and left hepatic ducts, which meet to form the common hepatic duct. This is joined by the cystic duct from the gall bladder, which then forms the common bile duct. The common bile duct joins the intestine at the duodenum through a valve called the Sphinter of Oddi.

The gall bladder is a pear-shaped bag 9cm long with a capacity of about 50ml. Breakdown products, such as bile salts, bilirubin, cholesterol, phospholipids, proteins, electrolytes and water are secreted by hepatocytes, and they are eventually transported down the bile ducts (this is bile and it is modified by cholangiocytes lining the bile ducts). The gall bladder stores bile, a greenish-yellow coloured liquid, which is delivered during a meal into the gut to assist with the breakdown (emulsifying) of fat in the food digested to allow easier absorption of fat and vitamins A, D,E and K. The liver produces approximately one pint (or 0.57 litres) of bile a day.

Disease of the biliary tract will interfere with this important function, as well as causing damage to the hepatocytes producing the breakdown products. About 10% of the populations of Western countries suffer with Gallstones, but less common diseases, such as Primary Biliary Cirrhosis and Primary Sclerosing Cholangitis can cause serious liver disease in some people suffering from them.

The parenchyma contains the hepatocytes, which absorb nutrients, and also detoxify and remove harmful substances from the blood. This is a relatively soft tissue, with a unique ability to regenerate after injury. Approximately three-quarters of the parenchyma needs to be damaged before sufficient hepatocytes are lost to impair liver function. When the liver suffers long term damage, scar tissue (fibrosis) forms and this disturbs hepatocyte function further. 

Normal liver under a microscope Fibrosed liver under a microscope
The Normal Liver under a Microscope   The Fibrosed Liver Under a Microscope

                 
If the whole of the liver is scarred (fibrosed), then this is known as cirrhosis. Initially a cirrhosed liver will continue to function, and this is known as compensated cirrhosis. If the liver function fails this is known as decompensated cirrhosis and without transplantation the outcome is likely to be fatal. Alcohol induced liver disease accounts for half of all adult liver disease, with about a third caused by viral hepatitis, and the remainder caused by a significant variety of diseases related to dysfunctional immune responses, metabolic disorders and inherited diseases.

functions of the liver

there are over 500 functions of the liver so here are a few of the more important functions:

  • processing digested food from the intestine

  • controlling levels of fats, amino acids and glucose in the blood

  • combating infections in the body

  • clearing the blood of particles and infections including bacteria

  • neutralising and destroying drugs and toxins

  • manufacturing bile 

  • storing iron, vitamins and other essential chemicals

  • breaking down food and turning it into energy

  • manufacturing, breaking down and regulating numerous hormones including sex hormones

  • making enzymes and proteins which are responsible for most chemical reactions in the body, for example those involved in blood clotting and repair of damaged tissues.

Some of the most important functions include:

Producing quick energy
One of the liver’s most important functions is to break down food and convert it into energy when needed. When energy is required in an emergency the liver rapidly converts its store of glycogen back into glucose ready for the body to use. Carbohydrates such as bread and potatoes from our diet are broken down to glucose and stored mainly in the liver and muscles as glycogen.

The liver also helps the body to get rid of waste products. Waste products which are not excreted by the kidneys are removed from the blood by the liver. Some of them pass into the duodenum and then into the bowel via the bile ducts.

People with liver damage may sometimes lose the ability to control glucose concentration in the blood and need a regular supply of sugar.

Fighting infections
The liver plays a vital role in fighting infections, particularly infections arising in the bowel. It does so by mobilising part of the body’s defence mechanism called the macrophage system. The liver contains over half of the body’s supply of macrophages (known as Kuppfer cells) which literally destroy any bacteria that they come into contact with.

disorders

What can go wrong?
The liver is a very uncomplaining organ with an enormous reserve. There is very little evidence of an ageing problem and in the absence of disease the liver functions fully right into old age. Most liver disease is symptomless and when there are symptoms they are often vague. There are hundreds of liver disorders but some are quite rare. The commonest ones are:

(To read in more depth see the liver 2.)

Hepatitis
Hepatitis literally means inflammation of the liver. Viruses are the commonest cause but there are others which are non viral, such as alcohol excess, the side effects of some drugs, both illegal and prescribed medicines. There is also a disease called autoimmune hepatitis.

Viral hepatitis
The liver can fall prey to an alphabet of viruses, namely hepatitis A, B, C, D, E and possibly G. There isn’t a hepatitis F - it’s been missed out so far! The main difference between the viruses is how they are spread and the effects they have on your health. Hepatitis A, B and C are the most common in the UK.

Hepatitis A is spread by eating food or drinking water which is contaminated with the hepatitis A virus, usually in countries where hygiene standards and sanitation are poor. There is a vaccine for this virus.

Hepatitis B is mainly passed on by blood to blood contact (blood borne) but also sexually. Worldwide hepatitis B kills between 1 - 2 million people annually, yet there is a vaccine to prevent infection. Blood transfusions have been screened in the UK since the 1970s. Hepatitis B is considerably more infectious than HIV.

Hepatitis C is also a blood borne virus. Prior to September 1991 a few people were infected by contaminated blood transfusions and blood products. Since then all blood donations have been screened for the virus. In some people the route of infection is not known but in many others injecting drugs is the cause. Users are thought to become infected by sharing injecting equipment. It takes just a tiny amount of blood from someone who carries the virus to spread the infection if it gets into someone else’s bloodstream.

Most people recover from hepatitis A with no lasting liver damage but B and C can cause long term liver disease, leading to cirrhosis and even liver cancer. In many cases there are no early warning symptoms until liver damage is far advanced.

Autoimmune hepatitis
This disease mainly affects women, usually just after the onset of puberty or around the time of the menopause. It is thought to be caused by the body’s defence system malfunctioning and attacking the liver. The commonest symptom in the early stages is fatigue and generally feeling unwell. However, the condition can be controlled with drugs which work by dampening down the immune system’s reaction to the liver.

Cirrhosis
It is a popular misconception that cirrhosis and hence liver disease only affects men who drink too much alcohol over the years. Cirrhosis can affect both men and women and can result from long term infection with hepatitis B and C viruses, inherited liver disorders such as haemochromatosis, bile duct diseases like primary biliary cirrhosis, as well as alcohol misuse.

The onset of cirrhosis is usually silent with few early warning symptoms. Cirrhosis is a result of long term continuous liver damage. If the liver is damaged for a short time some of the cells die and the liver regrows to its original size and shape. When the inflammation is severe and continuous, scar tissue called fibrosis develops. Smooth liver tissue is replaced by irregular nodules and the liver becomes much harder than normal. The combination of modules and fibrosis is called cirrhosis.

Once cirrhosis has developed it is usually considered irreversible, even if the inflammation which caused it improves. Recent studies in treating hepatitis C with interferon alpha or pegylated interferon alpha have suggested that there can be some reversal in fibrosis and even cirrhosis, but more studies are required and it is not known if this also applies to other liver diseases.

Alcoholic liver disease
Not everyone who drinks too much alcohol develops liver damage. It is still unclear why only some do but there is some evidence that it could be due in part to a combination of factors including a genetic susceptibility.

Consistent heavy drinking can lead to what is known as a fatty liver in which the liver cells become engorged with excess fat, more seriously an inflamed liver - alcoholic hepatitis - or, most seriously, a permanently scarred and damaged liver - cirrhosis.

In general the more you drink, and the greater the frequency and duration of heavy drinking, the more likely you are to develop cirrhosis.

Gallstones and gallbladder disease
Around 5 million people in the UK, approximately 10 per cent of the population, develop gallstones or another gallbladder disease at some time in their lives. Gallstones are lumps of solid material that form in the gallbladder and usually resemble small stones or gravel, although some can be as large as pebbles. Most are the size of a pea and may take many years to grow.

Anyone can get gallstones but middle aged, overweight women have the highest risk - fair, fat and forty traditionally describes a typical patient!

Inherited liver disease
It is possible to be born with a liver disease which may not produce symptoms until adulthood.

Haemochromatosis is an inherited metabolic disorder in which the body absorbs and stores more iron from food than it actually needs. It can prove fatal if not recognised and treated early enough. For many years haemochromatosis was thought to be rare. But recent research has discovered that the disease is much more common than first realised. In fact it is one of the commonest inherited disorders among people of Northern European origin and is estimated to affect 1 in 300.

Wilson's disease is also inherited and causes excessive amounts of copper to accumulate in the body. Copper, unlike other damaging metals such as lead and mercury, is essential to health. However, in Wilson’s disease the body’s inability to get rid of the excess results in an accumulation of copper in several organs. The liver is the first organ to store copper. When its storage capacity is exhausted, the overflow passes from the liver to the bloodstream and is carried to other organs, including the brain and the cornea of the eye. In a few cases the copper accumulation can result in psychiatric disorders or physical symptoms such as slurred speech, drooling or tremors.

Primary sclerosing chlangitis
Primary sclerosing cholangitis (PSC) is a bile duct disease in which the bile ducts inside and outside the liver become narrower because of inflammation and scarring. This causes the bile normally carried away by the ducts to stay within the liver, resulting in damage. It is not known what causes PSC but it often occurs in people with an inflammatory bowel disease, usually ulcerative colitis. Men are twice as likely to be affected as women, usually between the ages of 25 and 45, but it can also affect children as young as two years.

 

Primary Biliary Cirrhosis

In primary biliary cirrhosis (PBC) the patient’s immune system damages the small bile ducts inside the liver, so that bile cannot be efficiently secreted. The term PBC is really a misnomer because cirrhosis does not always follow, and if it does it can take many years to develop. Middle-aged women are most commonly affected, but the disease can affect anyone.

Paracetamol poisoning
Accidental or deliberate self-poisoning with paracetamol has been a serious cause of liver disease and transplantation in the UK, but in recent years it has declined - possibly due to a change in pack sizes on sale to the general public. A useful resource on this issue is the Paracetamol Information Centre.


Cancer of the liver
Cancer of the liver is divided into two main types: Primary Cancer (hepatocellular carcinoma) which means cancer that starts in the liver, and Secondary or Metastatic Cancer which means cancer that spreads to the liver from another part of the body. There is estimated 2,500 new cases of Primary Liver Cancer and 70,000 new cases of Secondary Liver Cancer every year in the UK.

In the UK most people who develop primary liver cancer have cirrhosis which can be from any cause. Primary liver cancer is not easy to diagnose in the early stages because its symptoms are usually vague. Typical symptoms include loss of appetite, weight loss, a general feeling of poor health, jaundice, fever, fatigue and weakness.

 

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