Snake venoms are generally produced in specific venom glands, derived from
salivary glands, the exception being Duvernoys glands in some Colubrid
species. The venom, once produced, is delivered by a duct to the fang base,
where it is transported into the victim either by a groove in the fang, or through
a fang duct. Contraction of muscles around the gland producing intra-glandular
pressure are the usual mode of venom transport, often allowing the snake to
fine-tune how much venom is expended in a given bite. This may explain,
in part, why many venomous snakes exhibit the dry bite phenomenon,
whereby a bite fails to inject enough venom to cause medically significant envenoming.
Snake venoms generally consist of a complex mixture of substances, each of which
may exhibit one or more distinct toxic actions. Many of the most potent snake
toxins have evolved highly specific targets, such as the neuromuscular junction
or components of the haemostatic system. It is likely all snake venoms fulfil
multiple functions for the snake, principally:
Defense against predators
There are many ways of classifying snake venoms; some still frequently used
in medical texts are misleading or inaccurate. Foremost amongst these is the
old aphorism that Elapids are neurotoxic and Viperids are haemorrhagic, a classification
that is quite inaccurate and should be abandoned. Some of the most potent toxins
active against human haemostasis are found in some Elapid venoms, while some
other Elapid species cause major local tissue injury at the bite site. Conversely,
there are a number of Viperid species whose principal clinical effect is neurotoxic
paralysis and which produce no or minimal effect on either local tissues at
the bite site or on the haemostatic system. From a medical perspective, a classification
based on clinical effects is generally useful and will be adopted widely on
this site, but the user should be aware that more biochemically based classifications
of venoms yield a quite different picture and that some medically important
toxins from snake venoms have several physiologically distinct actions, each
caused by separate regions of the toxin structure.
Various; interfere with haemostasis, necrotic, haemolytic
Various; autonomic etc
Nerve growth factors
Various or ill-defined
Nucleosides & nucleotides
It is also important to understand that there may be considerable variability
in venom composition even within a species, let alone between closely related
species, and even within an individual animal over time.
It is also important to understand that there are several different ways of
measuring venom toxicity that may yield quite different
comparitive results. Also, choice of animal for lethality studies can be crucial,
as can route of injection, again making comparisons between species difficult.
IMPORTANT INFORMATION FOR ALL SITE USERS
: The principle aim of this site is to provide
information useful to improving outcomes for humans suffering from envenoming or poisoning by
animals, plants or mushrooms. We make a reasonable attempt to verify accuracy of information
listed on this site. However, we cannot access every published paper of potential relevance,
either because they are not available to us or are in a language we cannot translate internally.
Equally, we cannot list knowledge which is not yet reported or known. It should not be assumed
that humankind currently knows all there is to know about any species, even for common species.
Further, we cannot control how users will interpret the information provided on this site. We
therefore do not accept legal responsibility for use of the information provided and we require
that all users use information from this site at their own risk.
The following should also be noted when reading information contained within the databases on this website: italics for scientific nomenclature cannot be displayed, and superscripting and subscripting is absent in some instances.