Thermoregulation Objectives 1. Measure the thermal status of terrestrial and marine mammals. 2. Compare the effectiveness of fur, blubber, skin, and neoprene as insulators. 3. Evaluate the effect of exercise on thermoregulation. 4. Identify thermal windows for terrestrial and marine mammals. Background One of the biggest challenges for mammals as homeotherms is maintaining a stable core body temperature. Because water can transfer heat 25 times faster than air of the same temperature, thermoregulation is particularly challenging for aquatic species. Wild mammals retain heat by using blubber or fur as a thermal barrier between their core body temperature and the environment. In comparison, humans rely on insulating materials such as down jackets in polar climates or neoprene suits in water. Insulation can lead to a build-up of body heat if it is too efficient. For many wellinsulated animals, thermal windows are used for the release of excess heat when the animals encounter warm environments or during high levels of activity. In this lab, we will compare the effectiveness of different types of insulation and the use of thermal windows in terrestrial and marine mammals. Skin temperature measurements will be taken using infrared thermometry and students will identify thermal windows. Part 1: Comparative Insulation Skin temperature is a good indicator of the quality of insulation of an animal. By measuring differences in the environmental temperature of the medium (air or water) and surface temperature, we can assess the gradient for heat loss. For example, surface temperatures that approximate environmental temperatures indicate better insulation by the tissues lying below the surface. To compare the quality of insulation provided by different thermal barriers, we will measure surface temperature for animals using different insulation and living in different thermal environments. Fill in the following table (on the next page) as these measurements are made for terrestrial and marine mammals. 1
Table 1: Temperature of insulated areas at rest. Temperature ( C) Air/Water Temperature ( C) Ambient Conditions (sun, shade, rain, wind, etc.) Thermal Gradient (skin temp air/water temp) Dog Fur Dolphin Blubber skin wetsuit Subjects: For each class group you will compare the surface temperature and thermal gradient on the mid-dorsal surface (mid-back) for 1) a dog resting in air, 2) dolphins resting in water, 3) humans resting in air with normal clothing, and 4) humans resting in air with a wetsuit. Ambient conditions should be noted for each subject. Your group should select one individual for the wetsuit tests. The wetsuit subject should change at the beginning of class and will be used throughout the session. In addition, each person should record their own skin temperature and calculate the thermal gradient from heat transfer using the following equation: Thermal Gradient ( C) = surface temperature air/water temperature Note: the larger the heat gradient, the higher the capacity for heat transfer. For these measurements you will be using an infared thermal sensor. When you depress the trigger, the infared temperature sensor will provide a digital read-out of the temperature in Celsius. Take 3-5 readings for each subject and average the results for the table. Air temperature and water temperature can be obtained by aiming the sensor at a neutral surface (water surface, classroom wall, shaded surface, etc.). SAFTEY WARNING: the infared sensors have a laser guide to help you make measurements of precise locations on the body. NEVER point the laser into anyone s eyes (human or animal)!!!! 2
Below: draw 2 bar graphs comparing the pre-exercise surface temperature and the thermal gradient values for each type of surface measured. Temp. ( C) SKIN WETSUIT BLUBBER FUR Thermal Gradient ( C) SKIN WETSUIT BLUBBER FUR 3
Based on the graphs drawn on the previous page, which material provided the best insulation? Part 2: Thermal Windows For well-insulated animals, several anatomical sites may serve as thermal windows. These are poorly insulated areas such as the periphery that are often associated with counter-current vascular arrangements. When the thermal windows are open, surface temperatures of these areas are higher than the remainder of the body, indicating high levels of heat flow. Note that thermal windows may be preferentially open or shut, depending on the thermal status of the animal. If the animal is trying to retain heat, it will reduce blood flow to the thermal windows, and those areas will become cooler. If the animal is able to or needs to dump heat, it will increase blood flow to the thermal windows, and those areas will become warm. With the same subjects as Part 1, you will identify each subject s thermal windows by infrared thermometry using an infrared thermal sensor. Remember: NEVER point the laser into anyone s eyes (human or animal). For the following animals, indicate the surface temperatures of the measurement sites on the drawings. For each animal, you will measure the surface temperatures for the following sites: side, belly, axillary, ear, foot/fin, tail/fluke. These measurements will be take pre- and postexercise. For HUMAN SUBJECTS (with and without wetsuit): take all pre-exercise measurements then have the human subject jump-rope for 3 minutes. Record the temperature along those same 6 locations again. For the DOG SUBJECT: once all the groups have completed the resting measurements, the dog will then go for a short jog with a handler and then post-exercise measurements will be taken. For the DOLPHIN SUBJECT: once all the groups have completed the resting measurements, the trainers will have the animals perform a series of high energy jumps and the post-exercise measurements will be taken. 4
PRE-EXERCISE SURFACE TEMPERATURES: POST-EXERCISE SURFACE TEMPERATURES 5
Table 2: Identify the location of the thermal window(s) for each subject. Record pre-exercise and post-exercise temperatures at each thermal window and the thermal gradient calculated for each thermal window. Subject (form of insulation) Thermal Window Location(s) Air/Water Temp ( C) Temp ( C) Post-Exercise Temp ( C) Thermal Gradient (skin temp air/water temp) Post-Exercise Thermal Gradient (skin temp air/water temp) Dog (fur) Dolphin (blubber) (skin) (wetsuit) On the graph below, create a line plot for the surface temperatures for each of the subjects measured at rest. Use a different color for each subject. (Note that a grouped bar graph would be more appropriate, but a line plot is easier to draw by hand.) Circle the names of the sites for each species that appeared to serve as thermal windows. Side Belly Axillary Ear Foot/Fin Tail/Fluke 6
1. Did the thermal windows appear to be open or shut for the different animals? Why? Did this differ between pre- and post- exercise? 2. Would you expect other anatomical areas to serve as thermal windows? Which ones? 3. What was the overall effect of exercise on the thermal windows? Be sure to discuss thermal gradients in your answer. 7