Detoxification (biotransformation)

The liver is the organ of the body that is particularly capable of breaking down toxins. Like a sewage treatment plant, all substances from food must pass through the liver before they enter the general bloodstream. However, not only nutrients but also the body’s own metabolic products can become toxic.

They are also converted into less toxic substances in the liver. Alcohol, which is a strong cell poison, is almost exclusively broken down in the liver (detoxification). By means of special proteins (enzymes), the alcohol is chemically modified in such a way that it is no longer harmful but, on the contrary, useful.

At the end of the alcohol degradation process, a substance is produced which directly supplies energy. Before you misunderstand this fact, however, there is more to consider: the liver does not manage to break down all the alcohol directly on the first passage; thus the poison reaches all the cells of the body via the bloodstream. Furthermore, alcohol is also poisonous to the liver cells themselves; this is where the liver cells die.

In addition, when alcohol is broken down, so much energy is produced that the liver can no longer keep up with it. It then stores the energy in the form of fat. If too much of this fat accumulates, a fatty liver (steatosis hepatis) develops; the precursor of liver cirrhosis.

The same principle applies to drugs: as they flow through the liver, the substances are chemically altered by special proteins to such an extent that they lose their effect (first-pass effect). In drug therapy, this effect is always taken into account when choosing the dosage. This can be so pronounced that some drugs cannot be administered in tablet form.

In rare cases, however, more toxic substances are formed by these processes. An important example is the combination of alcohol and paracetamol (painkiller), which can lead to the formation of a carcinogenic substance. A detoxification reaction of the liver, which is particularly important for medical diagnosis, is the conversion of bilirubin.

Bilirubin is formed wherever red blood cells are broken down or die. In both cases, this poisonous bilirubin, known as unconjugated or indirect, binds to a special protein in the blood, albumin. When this complex of protein and bilirubin finally reaches the liver, this bilirubin is released from its transport protein and remodeled in the liver cells so that it becomes non-toxic.

After its conversion it is called direct or conjugated. From the ratio of direct and indirect bilirubin, the physician can determine where damage may have occurred. Another important detoxification reaction of the liver is the formation of urea. Urea contains ammonia, a substance from protein metabolism, which in its natural form damages the brain, but is non-toxic in its compound as urea. This means that the body can simply excrete the previously toxic ammonia in the urine (hence the name).