Medical Matters: When we think of the body getting rid of waste products, our kidneys and bowels come most readily to mind. However there are other excretory organs in the body which go about their business in a less obvious way.
George Best's most recent troubles - he was given a 20-month driving ban for being two and a half times over the legal alcohol limit last week - are a reminder of the importance of the liver to human functioning. Despite receiving a liver transplant in July 2002, one of the greatest footballers of all time continues his battle with alcohol addiction.
Best needed a new liver because the one he was born with failed under the strain of years of abuse. Now there are fears the donor organ could go the same way, leading to his premature death.
The liver is a truly multifaceted organ. It produces proteins for the body; makes a substance called bile by breaking down part of the blood pigment (haemoglobin); stores iron and vitamins; destroys old blood cells; and makes the clotting agents that ensure blood clots.
One of the organ's main functions - and one that is central to human life - is its role in inactivating hormones. Some are broken down completely by the liver, others are combined in the liver with other substances to render the hormone harmless.
Many drugs, including alcohol, are also processed by the liver. After paracetamol and other medications have performed their desired function, it is the liver that inactivates them. If a person has liver disease, drug dosages must be modified to take into account the fact that they will be broken down at a different pace than usual. A normal dose may be an overdose for the patient with liver disease because of an inability to destroy the drug properly.
The liver is the most important site in the body for the metabolism of drugs. They are converted from fat-soluble to water-soluble substances that can be excreted in urine or via bile from the liver itself. Drug breakdown takes place in two stages: enzymes, and in particular a series called cytochrome P450, first of all break the drug down into its constituent parts.
In the second phase, these "bits" are joined up with other chemicals. Referred to as conjugates, the drug products are now in a form that prevents their re-absorption by the body. They can pass freely from the body in urine or bile.
There are a number of important factors influencing how the liver processes alcohol and other drugs: the health of the enzyme system within the liver cells; whether the drug was given orally, rectally or intravenously; the flow of blood through the liver; and whether different medications are competing for the organ's capacity to deal with them.
About one litre of bile flows from the liver every day, with 50 per cent flowing directly into the small intestine. The other 50 per cent is diverted into the gall bladder. Much of the bile is reabsorbed, but in the case of the breakdown products of drugs with the bile, these are excreted in the stools.
Alcohol increases the storage of fat in the liver. Over a period of over-indulgence, liver function begins to decrease. Eventually cirrhosis sets in, leading to liver failure. However, the organ maintains an amazing capacity for regeneration right up to end-stage liver failure.
Skin is an even more unlikely excretory organ. In fact, after the liver, it is the body's largest organ of elimination. We actually sweat water and salts from our skin pores. This is not just a random act but part of the body's regulatory armamentorium.
It explains why drinking lots of water helps our skin complexion and how skin responds so quickly to a change in diet or a period of detoxification. The teenager with acne is a victim of the body's desire to excrete oily substances.
Liver and skin play a vital role in keeping our bodies healthy. Both deserve to be treated with respect. Unfortunately for George Best, his addiction has made this a difficult goal and he is at real risk of destroying a second liver.
Dr Muiris Houston is pleased to hear from readers at mhouston@irish-times.ie. He regrets he cannot answer individual medical queries.