Any substance that causes injury, illness, or death, especially by chemical means. In biology, the word poison is reserved for substances that are most likely to enter the body via the mouth or airways. Poisonous substances injected by biting or stinging animals are called venom, while those released by bacteria in an infection are known as toxins. The liver removes some poisons from the blood. The majority of poisons may be divided into corrosives, such as sulphuric, nitric, and hydrochloric acids; irritants, including arsenic and copper sulphate; narcotics, such as opium and carbon monoxide; and narcotico-irritants, from any substances of plant origin including phenol acid and tobacco.
How poisons work Corrosives all burn and destroy the parts of the body with which they come into contact; irritants have an irritating effect on the stomach and bowels; narcotics affect the brainstem and spinal cord, inducing a stupor; and narcotico-irritants can cause intense irritations and finally act as narcotics.
At the molecular level, many poisons address one specific biochemical receptor, transporter, or channel. For instance, both carbon monoxide and cyanide ions bind irreversibly to the oxygen transporter haemoglobin, and thereby lead to internal suffocation.
Treatment In noncorrosive poisoning every effort is made to remove the poison from the system as soon as possible, usually by gastric lavage (stomach ‘washout’). For some corrosive and irritant poisons there are chemical antidotes, but for recently developed poisons in a new category (for example, the weedkiller paraquat) that produce proliferative changes in the system, there is no specific antidote. In the UK, the National Poisons Information Service, which was founded in 1963, provides eight regional centres in major city hospitals, where data on cases of poisoning is collected. Poisoning incidents (mostly self-poisonings) are a major cause of admission to acute medical wards.
Legislation and disposal In most countries the sale of poison to individuals is carefully controlled by law and, in general, only qualified and registered pharmacists and medical practitioners may dispense them. However, industrial and agricultural poisons are dumped into rivers and seas and on land, entering the food chain.
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