Toxin

Image:BlackWidowSpider.jpeg

For a list of biologically injurious substances, including toxins and other materials, as well as their effects, see poison.

A toxin (Gk.toxikon "(poison) for use on arrows,") is a poisonoussubstance produced by living cells or organisms. Toxins are nearly always proteinsthat are capable of causing disease on contact or absorption with body tissuesby interacting with biological macromoleculessuch as enzymesor cellular receptors. Toxins vary greatly in their severity, ranging from usually minor and acute (as in a beesting) to almost immediately deadly (as in botulinum toxin).

Biotoxins vary greatly in purpose and mechanism, and can be highly complex (the venom of the cone snailcontains dozens of small proteins, each targeting a specific nerve channel or receptor), or relatively small protein.

Use

Biotoxins are used in nature for two primary reasons:

• Predation (spider, snake, jellyfish, wasp)
• Defense (poison dart frog, deadly nightshade, honeybee, wasp)

Some of the more well known types of biotoxins include:

• Hemotoxins target and destroy red blood cells, and are transmitted through the bloodstream. Organisms that possess hemotoxins include:
  • Many vipers including rattlesnakes.
• Necrotoxins cause necrosis (i.e., death) in the cells they encounter and destroy all types of tissue. Necrotoxins spread through the bloodstream, but infect all tissues. In humans, skinand muscletissues are most sensitive to necrotoxins. Organisms that possess necrotoxins include:
  • The brown recluseor "fiddle back" spider.
  • Necrotizing fasciitis(the "flesh eating" bacteria)
• Neurotoxins primarily affect the nervous systems of animals. Organisms that possess neurotoxins include:
  • The black widowand other widow spiders.
  • The box jellyfish.
  • Elapidsnakes.

When toxins are generated by bacteria, they are called toxoids. The toxins may be produced either in the living body during infection(for instance, by tetanus) or by bacteria in dead biological material.

In the context of complementary medicinethe term is often used as a broader category of any harmful substance claimed to cause ill health, though mainstream scientists argue that the nature of such substances is usually unproven. Many publishers of non-technical material, such as the BBC, also follow this usage to refer to toxicsubstances in general, though some such as The Guardianmaintain the distinction that toxins are only those produced by living organisms.

Non-technical usage

When used non-technically, the term "toxin" is often applied to any toxicsubstances. Toxic substances not of biological origin are more properly termed poisons.

Practitioners of alternative medicineoften apply the term in a non-specific manner to refer to a broad category of harmful substances claimed to cause ill health.

See also

• Apitoxin
• Hemotoxin
• Neurotoxin
• List of fictional toxins

External links

• Society of Toxicology
• Cycad toxicity
• Corrections and clarifications, The Guardian, 30 May, 2005.fr:Toxine

he:רעלן ja:毒素 nl:Toxine

This article is licensed under the GNU Free Documentation License.
It uses material from the http://en.wikipedia.org/wiki/Toxin Wikipedia article Toxin.