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Life Lines The Science Podcast from The American Physiological Society Questions and Answers From Episode 3 Physiology of the Season The American Physiological Society 9650 Rockville Pike • Bethesda, MD 20814 • 301-634-7171 Life Lines, Episode 3 Physiology of the Season lifelines.tv Question Sheet Physiology of the Season 1) Name 3 physiological adaptations that reindeer have which enable them to survive frigid conditions during a long period of time during the winter and explain how the adaptations work. 2) “Rudolf the red-nosed reindeer” according to the song, was said to have a red and shiny nose.” Do reindeer have red noses? 3) Reindeer stand on ice and snow much of the time, which causes their limbs to be colder due to the ambient temperature which is conductive. What is a mechanism that helps to prevent membranes in their limbs from freezing? 4) Reindeer may travel large distances with widely fluctuating temperatures. In traveling to warmer temperatures, what limits their ability to get rid of excess heat and could impede their function? 5) If temperatures keep getting hotter, reindeer respond by “blowing off” as much heat as possible by panting. How does panting, which is a physiological adaptation, help to get rid of heat and keep animals like reindeer, cool? 6) In addition to removing excess heat, what is another consequence of panting that can be a problem for the animal? Life Lines, Episode 3 Physiology of the Season lifelines.tv 7) What are examples of adaptations that humans have to help them to deal with the cold? Think about Santa’s physical appearance living in the North Pole, being exposed to the elements, doing work and probably eating well. 8) What are behavioral adaptations that humans use to minimize heat loss? 9) Adaptations help in dealing with the cold, but they don’t mean that one is not getting cold. What physiological adaptation might Santa’s red rosy cheeks indicate? 10) In thinking about ‘”Santa” who lives in the North Pole, what are some behavioral adjustments that people who are well-adapted for living in a cold climate can do when they have to go to a warm climate and need to cool off? 11) Give two examples of physiological adaptations to a warm environment and explain how they cool the body. 12) How do humid conditions affect the ability to regulate body temperature? 13) During hot temperatures, how can one stay cool and prevent dehydration? 14) What happens if you get severely dehydrated? Life Lines, Episode 3 Physiology of the Season lifelines.tv 15) Sweating is a primary mechanism that humans use to cool down in the heat. When you start getting low on water, name a hormone that the body releases which tells you that you are getting thirsty and explain one way that it helps you to conserve water. Life Lines, Episode 3 Physiology of the Season lifelines.tv Question and Answer Sheet Physiology of the Season 1) Name 3 physiological adaptations that reindeer have which enable them to survive frigid conditions during a long period of time during the winter and explain how the adaptations work. Answer: Reindeer have: 1) a thick subcutaneous fat layer underneath the skin that may be as much as 2 inches thick. This thick store of fat insulates the reindeer from the outside cold and helps to keep the core body temperature warm. 2) a thick hair coat which provides substantial insulation from the cold and helps conserve body heat. The insulating ability of the thick hair coat is improved by their hollow-fibered hair which traps air within the hair follicle, as well as within the under-fur. 3) a countercurrent mechanism for heat exchange which reduces the flow of cold blood from extremities that are exposed to warm blood coming from their core. This allows them to conserve the heat in blood by decreasing the rate at which the cold blood returning from the limb draws heat from the incoming blood. These 3 mechanisms all act to decrease heat loss from the reindeer. Additionally, the fat also serves as an energy reserve. Reindeer don’t eat as much in the winter and their metabolic rate is less. Teacher note: It may be interesting to note sex differences with regard to body fat reserve. After mating season, male reindeer go into winter in relatively poor condition with approximately 5% body fat at a time when they have to deal with 45°F temperatures, which can be more challenging for male compared to female reindeer. 2) “Rudolf the red-nosed reindeer” according to the song, was said to have a red and shiny nose.” Do reindeer have red noses? Answer: Reindeer are covered in fur except for their hoofs and eyes. They have furry noses that are usually the white and grey colors of their snout. Fur provides good insulation which is important in a cold environment, since anything moist and exposed is likely to freeze unless there is very good blood flow to the exposed tissue. Note that there would be a high metabolic cost to maintain the blood flow under the frigid conditions. 3) Reindeer stand on ice and snow much of the time, which causes their limbs to be colder due to the ambient temperature which is conductive. What is a mechanism that helps to prevent membranes in their limbs from freezing? Life Lines, Episode 3 Physiology of the Season lifelines.tv Answer: Fatty acids in membranes in reindeer limbs become more and more unsaturated closer to the hoofs. The change in the composition of the membranes prevents membranes from freezing. Additionally, this prevents reindeer from feeling the cold as much. 4) Reindeer may travel large distances with widely fluctuating temperatures. In traveling to warmer temperatures, what limits their ability to get rid of excess heat and could impede their function? Answer: It becomes more difficult for reindeer to function at higher temperatures and exercise in warmer environments causes the body to warm up even faster. Insulation that enables them to adapt to temperatures such as -45°F limits their ability to get rid of excess heat when it becomes considerably warmer. If reindeer have already developed the thick winter coat and thick fat pads, it is difficult for them to keep cool enough for their muscles to keep functioning. Although the countercurrent mechanism which allows them to conserve heat in a cold climate can be regulated to allow them to dump heat at the body surface, the amount of insulation that they have at the time is still going to limit the ability to get rid of excess heat. 5) If temperatures keep getting hotter, reindeer respond by “blowing off” as much heat as possible by panting. How does panting, which is a physiological adaptation, help to get rid of heat and keep animals like reindeer, cool? Answer: Panting allows heat to be lost through ventilation. The wet (moist) surfaces of the mouth, palate and tongue are lined with water. Panting allows the blood that is flowing under these surfaces to release heat to the surface and to cause evaporation, a cooling process. Surface areas that are wet or moist remove the heat and cool the blood. Because there is a good level of blood flowing to this area, it can be used to remove a lot of heat from the animal. It is important to have as large a surface area as possible for this loss of heat. When animals pant, they open their mouths as much as possible and the tongue comes out and also maximizes the surface area that allows for evaporation and removal of heat from the blood flowing in the tongue. Parts of the animal that are not sweating or moist, or that don’t have much blood flow, will gain or generate heat. Sweating is not very effective for losing heat in animals that are covered in fur, such as reindeer. 6) In addition to removing excess heat, what is another consequence of panting that can be a problem for the animal? Answer: Panting also causes evaporation of a lot of moisture (loss of water) from the body. If animals are exposed to higher temperatures, they will need more water to replace the increase in water lost through panting. Life Lines, Episode 3 Physiology of the Season lifelines.tv 7) What are examples of adaptations that humans have to help them to deal with the cold? Think about Santa’s physical appearance living in the North Pole, being exposed to the elements, doing work and probably eating well. Answer: Santa is a large man with a large amount of subcutaneous fat that insulates his internal organs and decreases heat loss to the environment. Heat loss also has to do with a relationship called the surface area to body mass ratio. A large body has a smaller surface area to body mass ratio than a small body. The smaller body surface to body mass ratio favors a slower loss of heat to the environment and is an advantage for living in the cold. Babies and small animals like rodents have a large surface area to body mass ratio which causes a more rapid loss of heat to the environment. The surface area to body mass ratio is a critical determinant for heat loss prevention. 8) What are behavioral adaptations that humans use to minimize heat loss? Answer: Humans can wear warm clothing. Santa wears a warm outfit including a hat, gloves, and boots. Behavioral adaptations like a beard which protects the face and cheeks also helps to minimize heat loss. Eating provides energy needed for the demands of living in the cold and is another adaptation. When you are cold, your metabolic rate increases. Expect people in a cold environment to have a greater food intake because they are using more energy to stay warm. 9) Adaptations help in dealing with the cold, but they don’t mean that one is not getting cold. What physiological adaptation might Santa’s red rosy cheeks indicate? Answer: The redness of the cheeks indicates a distribution of blood to the cheeks when this region of the face becomes cold. This is an example of a physiological response to the cold, which is an adaptation to help keep the face warm. Unlike a behavioral adaptation that occurs by a conscious behavior, this physiological response is an adaptation that occurs unconsciously and is an “automatic response.” In the cold, blood is normally shunted to the core of the body. However, the body can redistribute some blood flow to the surface of areas of the skin such as the cheeks by causing dilation of certain blood vessels. This mechanism helps to transfer heat from the body to protect the skin from getting too cold and to avoid frostbite. Teacher note: In animals or humans that are kept in the cold, shivering (which increases metabolic activity or rate) and vasoconstriction (which decreases blood flow to certain regions) are other examples of physiological responses to the cold. It is important to note that the physiological and behavioral adaptations are all related to one another and don’t occur separately. Instead, they occur in conjunction with one another to support the overall functioning of the body. Life Lines, Episode 3 Physiology of the Season lifelines.tv 10) In thinking about ‘”Santa” who lives in the North Pole, what are some behavioral adjustments that people who are well-adapted for living in a cold climate can do when they have to go to a warm climate and need to cool off? Answer: People can remove warm clothes. This is a behavioral adjustment that increases the amount of our body surface area that is exposed to a cooler temperature. Santa’s layer of fat limits his heat loss and makes him poorly adapted for migration to a warm climate. Santa could open his coat, take off his gloves and hat and remove his warm boots. The hands, feet and head have a large surface area that can be exposed to the air to help him cool off. Exposure of these areas of the skin helps cool the blood flowing through your hands and feet as it circulates to your core. 11) Give two examples of physiological adaptations to a warm environment and explain how they cool the body. Answer: Heat exposure leads to an increase in body temperature which acts to dilate blood vessels and shunt blood to the skin surface to dissipate the extra body heat by transferring it to the environment. This “vasodilation” is a physiological adaptation mediated by the autonomic nervous system (which you don’t have voluntary control over) that dissipates extra body heat. Blood is shunted from internal organs to the skin surface which transfers heat through the skin to the environment. The hands and feet are good for this because they have a high surface area for dissipating the heat. Sweating is a physiological adaptation that puts a “water” layer on the skin surface which evaporates and cools the skin, allowing heat to dissipate from the body. When water evaporates, it takes energy in the form of heat away from the body. In a hot environment it is important for the skin to “breathe.” Sweat that is stuck between the skin and fabric is not as effective in dissipating heat. Clothing that wicks moisture away from the skin surface helps the cooling process. Teacher note: Water is a good conductor of both heat and cold. In some conditions, when the skin is wet, heat energy can be transferred from the environment to the body, or cold can be transferred to the body. 12) How do humid conditions affect the ability to regulate body temperature? Answer: The humidity in the air affects the rate of evaporation. With a high humidity, the rate of evaporation is less and sweating is not as effective in cooling the body. 13) During hot temperatures, how can one stay cool and prevent dehydration? Answer: It is important to drink more fluids to maintain the hydration level and prevent dehydration. Drinking water frequently reduces the risk for heat stroke and dehydration. Since the body also loses electrolytes in hot temperatures, it is Life Lines, Episode 3 Physiology of the Season lifelines.tv important that minerals and salts are also replaced in addition to water. Drinking water with some electrolytes is good because you also lose salt in the sweat. People in many climates, especially if exercising rigorously, may need to think about drinking water or some sport drinks that replenish electrolytes. 14) What happens if you get severely dehydrated? Answer: Levels of dehydration seen in heat stroke can be 10-15%. This can cause the body to shut down because of the loss of water and a number of electrolytes necessary for cells and organs to function. Severe dehydration can also cause the blood to thicken or become more viscous which would make it more difficult for the heart to pump the blood to the body tissues and organs. Teacher note: Dehydration has many severe consequences and people who exercise can become chronically dehydrated if they don’t consume sufficient liquids. Behavioral adaptations are very important because the physiological mechanisms occur “automatically” and may become fatigued without sufficient support. This happens with heat stroke or with people who die from hyperthermia. Your body can adjust for some time, but it requires a significant amount of energy and that some other aspect of your functioning be shut off, at least partially and temporarily, to accommodate for the regulation of your core temperature. It is important to use the behavioral mechanisms that you have available in order to put less stress on your body for it to maintain temperature in either the heat or cold. Behavioral adaptations are more energetically efficient than physiological adaptations and provide an evolutionary advantage. For example, exposing the hands and feet and head to the environment by removing clothes can help dissipate heat to the environment and acts together with the physiological adjustments. 15) Sweating is a primary mechanism that humans use to cool down in the heat. When you start getting low on water, name a hormone that the body releases which tells you that you are getting thirsty and explain one way that it helps you to conserve water. Answer: Antidiuretic hormone (ADH) causes thirst and also prevents you from increasing your urine volume. ADH increases salt and water reabsorption and decreases fluid loss through the kidney. If you are dehydrated enough to stimulate this mechanism, you urinate less after you increase your drinking behavior. Teacher note: The body regulates many different variables such as temperature, electrolytes, and plasma or blood volume and maintains them in a very narrow range that we refer to as a set point.