Exotis ISSN 2398-2985

Reptiles

Snake anatomy and physiology

Contributor(s): Vetstream Ltd, David Perpinan

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Integument

  • As in mammals, the skin of snakes plays several crucial roles.
  • The skin is the cellular protective barrier against the external environment. By being a protective barrier, it serves to protect the body from microbes and parasites, resists abrasions, and buffers the internal environment from the extremes of the external environment.
  • The skin holds other tissues and organs in place while being elastic enough to allow for respiration, movement and growth .
  • The skin serves other roles such as physiologic regulation, sensory detection (eg pit organs in vipers and boas), respiration and coloration.
  • The snake’s skin consists of two main layers, the dermis and epidermis:
    • The epidermis is covered completely by keratin.
    • This layer of keratinous cells, stratum corneum, shields the living tissue below.
    • The stratum germinativum, the innermost layer of the epidermis, divides continuously to replace the outer layer of dead keratinous cells. As the cells in the stratum germinativum are pushed outward, they slowly flatten, die, and keratinize to form the stratum corneum.
    • The stratum corneum is composed of three layers, the Oberhautchen layer, the beta-keratin layer, and the alpha-keratin layer, from the surface inward, respectively.
    • The dermis consists of two layers, the stratum compactum and the stratum spongiosum. The stratum compactum is the inner most layer of the dermis and consists of densely knit connective tissue.
    • The stratum spongiosum consists of connective tissue, blood vessels, glands, nerve endings, and other cellular structures.
  • Ecdysis, or shedding of the skin, is a normal occurrence throughout the snake’s life:
    • Young snakes will shed much more often and begin to have a longer resting period as they reach adult size. Young snakes may shed every month.
    • Because the top layer of snake skin consists mostly of keratin, which is dead material, it is incapable of expanding during the snake’s growth process. Therefore, it needs to be shed every so often.
    • The cells of the upper stratum germinativum, the outer generation layer, begin to proliferate and differentiate. The germinative layer begins to divide producing new layers of cells. These new cells form the inner generation layer, which is the precursor to scales, or the outer generation layer, for the next ecdysis cycle. At this stage the new epidermal layer is ready. The Oberhautchen then fills with lymph and enzymatic action produces a cleavage zone and the old epidermis is shed.
    • Before a snake sheds, it secretes a lubricant underneath the outermost layer of skin. This is to assist with the shedding process. This lubricant is most noticeable on the snake’s eyes .
    • The eyes become opaque or blue in color due to this lubricant being secreted. Sometime after this optical opacity or dullness is noticed the snake will begin to shed its skin.
    • It can take a week or two before the entire shedding process is over; shedding should be repeated at regular intervals in a healthy adult.
    • The snake may attempt to use any furnishings in the enclosure to assist in removing the dead skin. For this reason, furnishings should not be so abrasive as to cause injury to the snake. The snake may also attempt to soak in its water bowl to assist in shedding. Water softens the old skin and makes it easier to remove.
    • If the humidity is too low, the snake may have problems shedding.
    • A snake sheds its entire outer layer of skin all at once. All snakes, with the exception of large boids, should shed in one piece. If there are numerous pieces of the snake’s shed skin or some still present on the snake, this is an abnormal shed . Snakes with abnormal shedding may need husbandry changes Snake husbandry or may have ectoparasites and should be checked thoroughly.
    • Age, nutrition, species, reproductive status, overall health, and hormonal balance also play a role in the frequency of ecdysis.
    • If some shedding is still present on the snake, soaking or spraying can be tried to assist in the removal of the skin. If skin is allowed to build up and not sloughed off naturally, infections can occur underneath the old skin.
    • While snakes are in shed, they should not be handled or fed. Their senses are dulled (eyes opaque) and because they feel vulnerable, they can also be very defensive. To avoid potential bites, handling is not recommended during this time. It is also unlikely the snake will eat, so feeding should not occur until after the snake has shed.
    • If offering live prey items, feeding should not occur while the snake is in shed due to the higher potential for rodent bites.
    • The external layer of the spectacle is also shed.
    • Shedding is mediated by the thyroid glands.
    • The shedding process usually takes about 2 weeks.
  • Snakes are either entirely or partially covered by overlapping scales. The surface of each scale is composed of beta-keratin while the interscalar space, or sutures, is composed of alpha-keratin. This distribution of keratin gives a protective covering while allowing for flexibility and expansion.
  • Certain mutations of colubrids are nearly scaleless; these animals may only have labial and ventral scales. The remainder of the body is covered in a smooth keratinous epidermis. This anomaly is a recessive homozygous trait. While these varieties are selected in captivity, they usually die much younger than the average for the species.
  • Snakes have paired scent glands at the base of their tails; these glands open at the outer edge of the cloaca. Other than these glands, the skin of snakes has practically no other gland.
  • A large amount of semi-solid, malodorous fluid is released for defensive behavior in some species and for courting behavior in other species.

Special cutaneous adaptations

  • There are a few special structures associated with the skin of snakes:
    • Male boids possess larger spurs  than the female .
    • Spurs are only present in members of the family Boidae (boas and pythons) and are vestigial pelvic structures.
    • Eyelids are transparent and fuse together, forming the spectacle .
  • Many snakes also have special sense organs on the head :
    • The older (in evolutionary scale) snake families such as the Boidae have labial pits , a series of depressions running along the dorsal border of the upper jaw. These function as rudimentary heat sensors.
    • In the more evolutionarily advanced species, such as the pit vipers, the heat sensing organs can actually focus on their prey, and are composed of bilateral, forward-facing pits midway between the nares and the eyes. They are supplied by branches of the trigeminal nerves, and, in the case of pit vipers, may be sensitive enough to detect changes of heat as small as 0.002°C/32°F.

Musculoskeletal system

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Cardiovascular system

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Respiratory system

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Nervous system

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Sensorial organs

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Digestive system

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Urinary system

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Endocrine and exocrine glands

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Reproductive

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Further Reading

Publications

Refereed papers

Other sources of information

  • Cheek R & Crane M (2017) Snakes. In: Exotic Animal Medicine for the Veterinary Technician. 3rd edn. Eds: Ballard B & Cheek R. Wiley-Blackwell. pp 137-181.
  • Girling S J (2013) Basic Reptile and Amphibian Anatomy and Physiology. In: Veterinary Nursing of Exotic Pets. 2nd edn. Wiley-Blackwell. pp 246-255.
  • Mader D R (2006) Ed Reptile Medicine and Surgery. Saunders Elsevier, USA. pp 1242.

Reproduced with permission from Bonnie Ballard & Ryan Cheek: Exotic Animal Medicine for the Veterinary Technician © 2017, and Simon J Girling: Veterinary Nursing of Exotic Pets © 2013, published by John Wiley & Sons.


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