Your body's defences

Toxins are substances that can harm us when they are ingested into the body. If asked to name some toxins, most people would mention alcohol, tobacco and caffeine first, and they would be right in so far as these are all substances that can cause significant harm to the body. They are deliberately ingested toxins, but there are many more that we don't consume deliberately and may not even be aware of. Some are in the air we breathe, the water we drink and the foods, even seemingly healthy ones, that we eat.

When you eat a strawberry that has been sprayed with pesticide to kill any bugs in the strawberry patch, you ingest the pesticide along with the vitamin C and antioxidants of the fruit. When you stand on a city street and breathe in, your lungs have to cope with a cocktail of exhaust fumes and other gases, among which is the oxygen we need to stay alive. When you drink mineral water, you could be consuming traces of antimony, a poison that has been found in plastic bottles, alongside the water we need for survival.

We are surrounded by toxins at every turn, no matter how hard we try to be healthy. Fortunately, however our bodies have ways of dealing with most of the substances they come into contact with.

To get into the body, toxins have to be inhaled, eaten or absorbed through the skin. The first-line defences try to prevent entry in the first place but, if they fail, there are second and third lines in waiting.

Respiratory System

When you breathe through your nose, some tiny hairs- cilia- filter out particles of dust and soot, which will be expelled the next time you sneeze or blow your nose. The mucous membranes lining the mouth and nose contain chemicals called lactoferrin, which destroys bacteria, and saliva also has a host of antibacterial ingredients. As air travels down the respiratory tract, more cilia and mucous membranes remove any unwanted particles and phlegm is produced to ferry them upwards, triggering sensors that induce us to cough.

Once in the lungs, the air enters sacs known as alveoli, and there the white blood cells identify any dust or potential toxins that have made it through the other defences and they release the appropriate toxin-killing cells. At least, this is the case in normal, healthy adults; those with asthma or other lung problems don't fight toxins quite so successfully.

Digestive System

When you eat or drink something, the antibacterial compounds in the mouth work on it first, and then stomach acid kills off a lot of potentially dangerous toxins before they get further down the intestine. Once in the intestine, beneficial bacteria help to defend the system from poisons while microscopic villi- little fingers which are lined with capillaries- absorb nutrients into the blood stream. The small intestine, which is 6m (20ft) in length, filters out any larger molecules and undigested foods and carries them down to be excreted when you have a bowl movement. Smaller molecules that are absorbed are carried in the first instance to the liver.

Liver and Gall Bladder

The liver is a multi-tasking organ which produces and processes hundreds of chemicals everyday. When blood arrives from the small intestine, the liver secretes enzymes that process vital nutrients into a form in which they can be used by the cells of the body. It stores excess glucose (sugar) as glycogen and produces cholesterol, a substance that helps the blood to carry fats around the body. It also clears the blood of drugs and poisons, breaking them down to neutralize them or turning them into a form in which they can be secreted as bile fluid.

Bile is transported from the liver to the gall bladder. When you next eat something containing fat, the bile is excreted into the small intestine to help the digestive process and, if the system is functioning effectively, the bile will then pass from your body in faeces.

Kidneys

The kidneys filter about 200 litres of blood everyday, sifting out waste products and excess water. A series of tiny tubes, called nephrons are the filtering units. Most of us will form about 2 litres (3 ½ pints) of urine a day from substances that are no longer needed by the body.

Spleen

Another of the body's filtering systems, the spleen removes worn-out red blood cells from circulation and recycles then into iron to build the blood. It also gets rid of any unhealthy bacteria, so it can stop you coming down with colds or flu when it is functioning efficiently.

Lymphatic System

White blood cells (the ones that fight diseases) are stored in lymph nodes situated under your arms, in your neck, around your spine and in your groin. You may be able to feel that your lymph nodes are swollen when you are fighting off an infection. A watery fluid called lymph is circulated round the body, mainly by the action of your muscles. The lymphatic system does not have a pump- in the way that the blood circulates due to the action of the heart- so it can be sluggish if you don't get much exercise.

In the cells, lymph is responsible for filtering out the waste products of cellular reactions and other toxins that have got into the tissues. It also carries white blood cells to sites of infection, where they adhere to and break down micro-organisms and debris that they recognize as foreign.

Skin

Some chemicals can pass through unbroken skin, but only very slowly. Thus the nicotine in nicotine patches makes its way into the bloodstream, and so do certain toxic chemicals, such as insecticides and solvents, which can cause problems.

The skin is also an organ for the secretion of waste products. As you heat up and perspire, you release a mixture of urea along with other toxins from the fatty tissues. The more you sweat, the more you release, which is why saunas can be an effective part of a general detox programme.