Hello everyone and welcome to this week's article, which is the first in a two-part series about the liver. In this week's article, I will be discussing the main functions of the liver and how the liver can be damaged. In next week's article, I will be exploring the possible treatments for damage to this organ.
What is the liver?
The liver is a human organ, which is found just underneath the rib cage. According to the British Liver Trust, the liver is the largest solid organ in the body (weighing around 1.8kg in men and 1.3kg in women). It is one of the most important organs in the body, due to the number of important roles it carries out.
One of the liver's most important functions is to remove toxins and other harmful substances from the body. The liver can either break down these toxins or modify them (e.g. by adding a methyl group). For example, following deamination of amino acids in the liver, the ammonia generated is converted to urea by the liver. The urea is then excreted through the kidneys. In addition, the liver is also involved with the endocrine system, as it breaks down hormones - if these hormones weren't removed from the blood, then they would continue to affect target organs for much longer than intended.
Furthermore, the liver also acts as a store of blood, as it is an expandable organ. This means that, by dilating blood vessels inside the liver, it can act as a reservoir for blood. Indeed, some sources estimate that as much as 10% of the body's total blood volume can be stored in the liver. This is incredibly important, as it can release this blood in times of low blood volume (e.g. after excessive blood loss), thus allowing the blood pressure and volume to remain high.
The liver also plays a significant role in metabolism, particularly carbohydrate metabolism. This is due to the fact that the liver converts glucose to glycogen. When we eat food, most of the carbohydrates we ingest are digested and hydrolysed into small, simpler sugars such as glucose.
Unfortunately, storing sugars can cause two main problems. Firstly, glucose is very reactive, which means that it can interfere with the reactions taking place in the cell. Additionally, glucose would also dissolve in the water inside cells, thus reducing the water potential of the cells. Water then moves into the cells by osmosis, causing them to burst.
This problem can be overcome by converting the glucose into glycogen - a dense and inert polysaccharide that can be hydrolysed when necessary to release glucose molecules for respiration. The synthesised glycogen is then stored in the liver and muscle cells. The liver is responsible for both of these conversions - insulin causes the liver to convert glucose to glycogen, while glucagon converts glycogen back into glucose.
In addition, the liver also has a variety of other functions. These functions include the production of bile (which is essential for the digestion of lipids), the synthesis of clotting factors, the production of cholesterol and triglycerides, and the fighting of infections.
Damage to the liver caused by toxins
One of the main ways that damage can be caused to the liver is by the ingestion of toxins (including alcohol and paracetamol). This can be through the ingestion of a large amount of a toxin at once, or by the build-up of these toxins in the liver. When these toxins build up, they damage the liver tissue. This damage is in the form of cirrhosis, which is where the healthy liver tissue is replaced by scar tissue, thus severely restricting the liver's ability to carry out its functions.
Additionally, drinking excess alcohol can also cause the build-up of fats in the liver. According to the NHS, fatty liver disease does not usually have symptoms and can be reversed by abstaining for alcohol for a few months.
There are many different causes of alcohol-related liver disease. People can be driven to drink excessively for a variety of reasons, including significant life events such as bereavement or divorce. In addition, recent years have seen a rise in depression and anxiety amongst young people, which could also increase the prevalence of excessive drinking. Furthermore, there are many other factors which can increase the chances of someone contracting alcohol-related liver diseases, including obesity and genetic factors.
Non-alcoholic fatty liver disease
According to the NHS, non-alcoholic fatty liver disease is used to describe a range of liver diseases, caused by the build-up of fat in the liver. In healthy people, the liver contains very little fat. Non-alcoholic fatty liver disease occurs when fat accumulates over time in the liver, causing inflammation and scarring.
Symptoms of non-alcoholic fatty liver disease include tiredness, weakness, unexplained weight loss and a dull pain around the liver. There are many risk factors which make non-alcoholic fatty liver disease more likely. These include having high blood pressure, having high cholesterol, being obese and smoking. Consequently, those who are at risk of suffering from this disease are encouraged to avoid high-cholesterol foods and exercise regularly.
Viral causes of liver diseases
Liver disease can also be caused by viral agents. There are five main viruses that cause damage to the liver - hepatitis A, hepatitis B, hepatitis C, hepatitis D and hepatitis E. These viruses all cause inflammation of the liver (i.e. hepatitis). Furthermore, other common symptoms of hepatitis infection include dark urine, itchy skin, jaundice (the yellowing of the eyes and skin), and muscle and joint pain. In the most severe cases, hepatitis infection can also cause scar tissue forming in the liver, leading to a loss of liver function.
The most common type of viral hepatitis in the UK is hepatitis C. This virus has been in the news recently, as The Nobel Prize in Physiology or Medicine 2020 was award to three people responsible for discovering this virus - Harvey Alter, Michael Houghton and Charles Rice. The discovery of the hepatitis C virus was a remarkable achievement, as it allowed highly sensitive blood tests for the virus to be developed. It also allowed for the development of specific antiviral drugs for hepatitis C.
Hepatitis viruses are some of the most deadly viruses in the world. According to the World Health Organisation, there are roughly 500 million people worldwide infected with this disease. Additionally, these viruses also kill approximately 1.5 million people each year. Consequently, governments across the globe invest huge amounts of resources in restricting the spread of this disease. For example, all babies in the UK are now provided with a vaccine against hepatitis B.
Liver cancer
Liver cancer occurs when a cell in the liver mutates, causing it to divide uncontrollably by mitosis. These dividing cells are sometimes not removed by the body, allowing them to continue to divide and form a tumour. Eventually, this tumour will grow so large that it invades other tissues and restricts the liver from carrying out its functions. In addition, liver cancer can also be caused by a group of cancerous cells from somewhere else in the body breaking off and attaching themselves to the liver.
There are many causes of liver cancer. These include lifestyle choices such as smoking, excessive alcohol consumption, lack of exercise and obesity. Additional causes include genetic predispositions and age. Furthermore, the diseases already mentioned in this article can also increase the chance of liver cancer occurring.
Inherited liver diseases
The functions of the liver can also be compromised through inherited liver diseases. One of these diseases is called haemochromatosis. Haemochromatosis is an inherited, recessive, genetic condition that changes how your body absorbs iron from food. This prevents sufferers from controlling the iron level in their blood, thus causing iron to build up in their organs (including the liver).
I hope you enjoyed this week's article which summarised the main functions of the liver and how the liver can be damaged. Make sure to subscribe to the mailing list below, so that you get notified when I publish next week's article, which will be about treating liver damage.
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