Jeff Baier MS DVM Birds of Prey Foundation Broomfield, CO drjeffbaier@gmail.com
Squamates Chelonians Snakes Lizards Varanids Monitor Lizards Crocodilians
Reptilian adaptations Anaerobic glycolysis Low metabolic rate Cardiovascular system Renal portal system
Based on aerobic metabolism reptiles are weaker than their mammalian counterparts Anaerobic glycolysis allows reptiles to exceed the strength of mammals for periods of time
Aerobic metabolism 70 kg human is five times stronger than 700 kg crocodilian Anaerobic metabolism Allows crocodilian to develop the strength of 20 humans
Anaerobic metabolism allows for the quick utilization of stored energy Lactic acid is produced No carbon dioxide is produced
Reptiles may utilized anaerobic metabolism when hospitalized Physical examination Restraint for diagnostic sampling
Fluid replacement considerations Patient likely to have significant lactate levels Fluid replacement using fluids containing lactate may be contraindicated
Suggestions for fluid replacement 2.5% Dextrose in 0.45% Saline Mixture of equal parts 5% Dextrose with Normosol
Suggestions for fluid replacement Slightly hypotonic fluids may be preferred Reptiles have higher intracellular volumes and lower plasma volume than mammals Replacement of intracellular volume appears to be important.
Metabolic rate is not constant for all reptilian species Trends As the size of the animal increases metabolic rate decreases Alligators have lower metabolic rate than anoles Cattle have lower metabolic rate than shrews
Trends As an individual grows and ages the metabolic rate decreases Neonates have higher metabolic rates than adults
Generally the metabolic rate of reptiles is lower than that of mammals of considerable size
Differences in metabolic rate Mammals Body temperature is constant Body temperature maintained internally
Differences in metabolic rate Reptiles Body temperature is not constant Body temperature maintained by a combination of metabolic heat and environmental heat
Activity temperature range Range of temperatures in which a reptilian species conducts normal activities At or above the upper limit animals cannot survive At or below lower limit animals can survive, if proper conditions exist
Within the activity temperature range for a species the animal will be able to maintain its preferred body temperature The temperature at which all physiological functions are optimal
Temperature preferences and disease state Reptiles in acute stages tend to seek out warm areas in their environment Reptiles in chronic stages of disease tend to seek out cooler areas in their environment
Metabolic rate and induction of anesthesia Induction with inhalant anesthetics is a slow process Respiration may be slowed due to presence of anesthetic agent Respiration may be slowed due to the high oxygen content
Oxygen consumption increases with temperature
Stroke volume in iguanas decreases as temperature increases Heart rate and oxygen delivery to tissues increases to compensate
Organ perfusion Perfusion of heart and kidney increase with temperature Once activity temperature range is exceeded, perfusion to these organs decreases
Antibiotics Volume of distribution Clearance rate MIC
Digestion Rate of passage Nutrient absorption, assimilation and utilization
Preferred body temperature Typically 28-34 O C Maintained through physical, behavioral and physiological factors Preferred activity range
Acid-Base Balance ph varies inversely with temperature
Water regulation Increased ambient temperature increases water loss
Adaptations of the cardiovascular system have allowed snakes to become a highly successful group Snakes utilize terrestrial, arboreal and aquatic habitats
Three Chambers Atria Left - filled by sinus venousum Right - filled by pulmonary veins Ventricle Subdivided into 3 interconnecting cava
Ventricular Cava Cavum arteriosum supplies blood to systemic circuit Cavum pulmonale supplied blood to pulmonary circuit Cavum venosum interconnects the c. arteriosum and c. pulmonale
The ventricle is considered a single pressure pump Pressure in each of the cava is equal during systole
Squamates - systemic and pulmonary circuits are in parallel arrangement Mammals - systemic and pulmonary circuits are in series
Cavum venousum reduced Admixture and intracardiac shunting of blood still possible Functions similar to mammalian heart
Right to left shunting of blood can occur during periods of apnea Shunting occurs through Foramen Panizzae
Shunting is controlled by systolic pressure differences Normal left sided pressure is higher than that of the right Apnea Right and left pressures equalize
Shunting Shunts can occur simultaneously in both directions Direction of the net shunt is determined by which circuit receives the majority of total cardiac output
Right to left shunting Diving Cooling Left to right shunting Basking Temporary L-R shunts occur during apnea Anticipatory L-R shunt prior to end of dive
Most commonly functions similar to four chambered heart Controlled shunting does occur
Control of shunting Regulation of peripheral resistance increased pulmonary resistance - right to left shunt increased systemic resistance - left to right shunt
Control of shunting Adjustments of cardiac excitation Ventilation - low velocity right to left depolarization Apnea - high velocity left to right depolarization
Matched ventilation and perfusion Right to left shunting during apnea allows ventilation and perfusion to remained matched, while maintaining systemic perfusion
Shunting does not save cardiac energy during apnea Right to left shunting during apnea does not allow for oxygen metering
Pulmonary bypass reduces plasma filtration into lungs Left to right shunting facilitates CO 2 elimination
Maintenance of core body temperature Right to left shunting facilitates warming Left to right shunting in conjunction with panting facilitates cooling
Arboreal Snakes must deal with the effects of gravity on their circulatory system
Arboreal snakes have the following adaptations Higher blood pressure Heart is located closer to the head Tightly adherent skin Good muscle tone The vascular lung is cranial to the heart and short in comparison with other snakes
Sea snakes live in an environment of near neutral buoyancy
Sea snakes have the following adaptations to their environment The heart is located near the mid-point of the body The vascular portion of the lung extends nearly the entire length of the body
Sea snakes lack the ability to compensate for gravitational effects on their circulatory system
Reptilian Kidney Unable to concentrate urine nephron lacks loop of Henle Glomerular filtration rate determined by the number of nephrons perfused
Veins arising in the caudal half of the body pass through the kidney prior to passing through the liver Blood passes over the renal tubules
Functions Water conservation Perfusion of the kidney
Thoughts on the renal portal system Therapeutic agents injected in the caudal half of the body may be cleared more rapidly Injections of potentially nephrotoxic agents made in the caudal portion of the body may increase the likelihood of nephrotoxicity
Blood in the renal portal system does not necessarily enter the kidney
Injection site does not appear to have clinically significant effect on pharmacokinetics
There does not appear to be elimination on first pass through the kidney
There does not appear to be accumulation of substances in the kidney
UV light is necessary for the synthesis of vitamin D Vitamin D is necessary for calcium absorbtion
Due to a lack of commercially formulated complete diets herpetoculturists must rely on UV lighting to meet the vitamin D requirements of captive reptiles
Light in the UVB spectrum is necessary for animals to produce Vitamin D Wavelength of approximately 290-320 nm
The amount of UV produced by a fluorescent tube decreases over time Fluorescent tubes should be replaced every six months
Fluorescent tubes do not produce UVB along their entire length Only 50% of the tube produces UVB
The portion of the tube that produces UVB is in the center of the bulb There is no UVB production at the ends of the tube
UV light transmission Window glass blocks nearly all UVB Acrylic panels block nearly all UVB UV transmissible Plexiglas blocks nearly 40% of UVB A typical screen aquarium top blocks approximately 30% of UVB
Intensity of UV light is affected by distance Inverse Square Law
Typical fluorescent light tubes used to provide UV light to reptiles have an effective distance of 18 inches
UVB Irradiance Distance from Light Source Light Source 6 inches 12 inches 24 inches Reptile Daylight 35.9 14.0 4.0 Sun Lamp (New) 460.0 175.2 55.0 Sun Lamp (Used) 249.0 100.4 33.7 Wonder Light (160) N/A 211.0 72.0 Wonder Light (300) N/A 400.0 130.0 Measurements in microwatts/cm 2
UVB Irradiance Distance from Light Source Light Source 6 inches 12 inches 24 inches Vitalight 4.7 2.0 0.9 Black Light 5.2 2.0 0.4 Cool White 5.6 0.9 0.0 Experimental Lamp 69.9 27.3 8.3 Reptisun 109.7 43.0 14.4 Measurements in microwatts/cm 2