Venomous Reptiles

Most people know that some species of snakes are venomous, but a lot of people don't know about the venomous lizards - the Gila Monster (Heloderma suspectum) and Bearded Lizard (Heloderma horridum). These lizards mostly eat eggs and young animals, which do not need venom to subdue. Their venom is instead used to defend themselves against predators. These lizards are not built to run away from predators, so they use venom as a last resort. Their venom includes compounds that cause severely reduced blood pressure, inflammation, and excruciating pain. Even though the venom isn't used to catch prey, it might still play some role in digestion. Certain peptides, or small chains of amino acids, in Heloderma venom mimic vertebrate hormones that, in mammals at least, help the animals digest food and metabolize carbohydrates (Beck, 1990). Unlike snakes whose venom is produced in a gland in the upper jaw, Gila monsters' and bearded lizards' venom is produced in a venom gland in the lower jaw. Venom ducts then transport the venom to the vicinity of the venom-conducting teeth. The capillary action of liquid then causes the venom to creep up the grooves in the teeth, where it is delivered to the target through a bite (Russell & Bogert, 1981). 

A baby bearded lizard (Image 1).

A bearded lizard (Image 2).

A gila monster (Image 3).

Snakes use venom for killing prey and defending themselves against predators. As I mentioned in my first post, snake venoms can either paralyse the target by disrupting its nervous system or coagulate the target's blood, which would disturb the cardiovascular system (Calvete, et al., 2009). The venom flows from the venom gland through the venom duct and to the fang. However, the venom duct is not physically attached to the fang.  Despite this, no leakage occurs when the venom is flowing to the fang. A seal is made by the tensed dental sheath stretching tightly around the fang base. This tension is formed when the fang pushes forwards during a bite, by the contraction of tendons running into the dental sheath and by the hydraulic pressure building up in the cavity. This tension causes the fang to slip forward between two hardened pads situated within the dental sheath wall, one on either side of the venom duct opening. This action seals the lateral sides of the fang and aligns it with the venom duct opening (Schaefer, 1976). 

A red-sided garter snake (Image 4). 

A diagram showing the location of the venom glands, venom ducts and fangs (Image 5).

References

Beck, D. (1990). Ecology and Behavior of the Gila Monster in Southwestern Utah. Journal of Herpetology , 54-68.

Calvete, et al. (2009). Venoms, venomics, antivenomics. FEBS Letters , 583 (11), 1736-1743.

Russell, F., & Bogert, C. (1981). Gila Monster: Its Biology, Venom and Bite -A Review. Toxicon , 19 (3), 341-359.

Schaefer, N. (1976). The Mechanism of Venom Transfer from the Venom Duct to the Fang in Snakes. Herpetologica , 71-76.

Images

Image 1 - http://www.animalfactguide.com/wp-content/uploads/2011/01/beaded-lizard-detail.jpg. Accessed on 08/04/14.

Image 2- http://www.helodermahorridum.com/images/large/lizardndetail.jpg. Accessed on 08/04/14.

Image 3 -https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhKr70tTXyJttkaDjK_xpwLYRLek36WeOosVl4pFZbk7K6JeFQPgLDd_Z_s26b9AxD-qBpm3Cte5iOTfN84LlF6toMwXnF2k8Z9g_aKe4K60K-a-JN0jFVX_DsmS30k9FiAuzl0sk2SFVg9/s1600/gila+monster.jpg. Accessed on 08/04/14.

Images 4 - http://images.nationalgeographic.com/wpf/media-live/photos/000/641/overrides/2013-year-of-the-snake-list_64139_600x450.jpg. Accessed on 08/04/14.

Image 5 - http://jeanbont.pbworks.com/f/1299294821/snake%20fangs%20and%20venom.png. Accessed on 08/04/14.