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Pharmacology => Poison => Venom
Venom
Venom, poison of animal origin, usually restricted to poisons that are administered by biting or stinging and used to capture-and, sometimes, aid in digesting-prey, or for defense. Thus the poisons secreted by the skin of some toads, or accumulated in the bodies of numerous inedible animals, are ordinarily not considered venoms. The most familiar venomous animals are certain snakes and insects and the spiders and other arachnids. Venomous species occur throughout the animal kingdom, however, including the mammals. Some shrews, for example, have venomous saliva, and the platypus bears poison spurs on its hind legs.
The severity of a venom's effects depends on several factors, such as its chemical nature, the stinging or biting mechanism involved, the amount of venom delivered, and the size and condition of the victim. For example, all spiders are venomous, but the venoms of most are too weak or minute in quantity to have noticeable effects on humans; in addition, many spiders cannot even puncture human skin. Thus, few of them are poisonous to humans, but their venoms are quite effective on insect prey.
Chemically, venoms vary greatly across the animal kingdom and are not readily defined. Snake venoms, for example, are complex mixtures of enzymatic proteins and different toxins. In terms of their effects, however, they may be broadly categorized as hemotoxic (damaging blood vessels and causing hemorrhage) or neurotoxic (paralyzing nerve centers that control respiration and heart action); they may also contain agents that promote or prevent blood clotting. Sometimes a combination of these effects is involved, however, and variations may occur within genera or even within species. Among snakes, cobras and coral snakes may be singled out as having a particularly neurotoxic venom; among other animals, the venom of arachnids also falls into the neurotoxic category. The effects of insect stings are usually the result of histamines that produce local irritation and swelling.
Serums against various venoms can be produced by injecting animals such as horses with sublethal doses and extracting the immune serum, or antivenin, that the animal body produces. Venoms themselves have occasional medicinal uses; for example, some are used as painkillers in cases of arthritis or cancer, and some serve as coagulants for people with hemophilia. See also Poison.
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