Regulating Body Temperature (1972)

[Applause] Okay. Check that probe. Make sure it's comfortable. >> That's all right. >> You'll be carrying that all day long. Now, will it be on your way for work? >> It feels pretty good. Pretty good. >> Go ahead. Get dressed and bring your Parker when you come back. See that? [Music] There you go. >> Okay. That holding on tight. >> Mhm. That's pretty good. >> You see your temperature coming out here already recording? >> Yeah. >> I don't want it coming loose. Now, you keep this Parker with you at all times, even when you're in your room tonight, cuz we'll be listening in on the air temperature on your radio there. >> Okay. I'll be in tomorrow morning. >> Okay. See you then. First pop. >> Okay. [Music] [Applause] [Music] Woo! [Music] Woo! How's the record look? >> Are you sure we're going in and out yesterday morning? Look at the >> We take it for granted that our body temperature will remain nearly constant no matter how much the air temperature may change. >> Jogging. Oh, no wonder. In fact, our body temperature seldom moves more than 1°ree above or below its normal temperature of about 37° centigrade. >> Our temperature yesterday, your body temperature didn't shift more than a degree and a half in spite of all the jogging. >> Yet, consider the range in environmental temperatures within which we and other animals must function. Some animals are often exposed to temperatures of more than 50° centigrade below freezing. Others live where temperatures may rise higher than 45° above freezing. Both kinds of animals share the ability to maintain a fairly high and nearly constant body temperature throughout life. How to explain this remarkable constancy? The heat that warms our bodies and those of other animals is produced by the cells. Heat is released during metabolism, the chemical reactions of life. If the temperature rises or falls, cell functions speed up or slow down. So the more constant body temperature remains, the better the cells and therefore an animal can function. Animals differ in how efficiently they are able to regulate their body temperature. This catfish, for example, normally it prefers a body temperature of around 27° centigrade. But in this divided tank, the water on one side is much colder and on the other much warmer than the animal prefers. Watch how the fish behaves when it is allowed to move at will between the two sides. The gate is triggered by an electric eye. Evidently, the fish is able to sense the difference between the two sides because it moves from side to side so that the body temperature remains nearly constant. In other words, the animal behaves in a way that will preserve its normal body functions. But if the animal is not allowed to leave the cold water. Soon the animal's body temperature cools to that of the environment. As a result, its body processes have slowed down. And it's the same with amphibians and reptiles. None of these animals produces enough heat in its cells to raise body temperature much above that of the environment. They must rely on external heat sources to keep warm and to maintain normal body functions. For this reason, they're called ectotherms, meaning heat from outside. With a few exceptions, only birds and mammals produce heat at such a high rate that they can keep their bodies warm even in cold surroundings. Such animals are called endootherms, meaning heat from within. Usually the bodies of endurms are warmer than their surroundings. As a result, they are continually losing heat to the cooler environment. So, if body temperature is to remain nearly constant, the body must lose heat no faster than it can produce heat from its food. In other words, heat loss must be balanced by heat gain. To maintain this balance, the body continually exchanges heat with the environment. The ways in which heat is gained or lost can be shown with a heat flow sensor. Okay, >> let's put on the heat flow sensor. >> The sensor measures calories of heat flowing into or out of the body. >> Let's try radiant heat gain from the heat lamp. Put your hand right up in front of the lamp. >> Heat is exchanged in a number of ways. By radiation, heat flowing through space. >> Okay. Yeah, fair enough. [Music] Let's try conductive now. Okay. >> Press your hand right onto the table. [Music] >> Oh, that's good. Table feels >> by conduction where the body is in contact with a cool or warm object. [Music] >> What happens if you blow on it? Let's try convective loss. Okay. >> By convection, cool or warm air blowing past the body. >> The body can lose or gain heat by any of these ways depending on which is warmer, body or environment. I'm just going to put a little bit of water on there. And then that was cooling from the water. Now it's watch evaporative cooling. If here's where it was no evaporation. This is due to evaporation. >> On the other hand, evaporation of moisture from the skin always results in heat loss. Heat exchange occurs in all ways simultaneously and changes from moment to moment. The body monitoring these changes by way of signals in the nervous system and the bloodstream makes continual adjustments in a large variety of ways. Through behavior, for example, when we or other animals feel hot or cold, we do something about it. behavior is the most common way of adjusting to heat or cold. Another way is by insulation. Fur and feathers insulate on the outside, fat on the inside. Man, basically a tropical animal survives in cold regions because he can change his insulation at will. But sometimes behavior and insulation are not sufficient to cope with the effects of a cold or hot environment. So to maintain its temperature constant, the body also makes delicate physiological adjustments. How and when these adjustments are made can best be studied in the laboratory. Note the conditions at the start of the experiment. >> Rectal temperature all right? >> Yes. >> Rectal temperature normal 36.8°. Room temperature a comfortable 28° centigrade. >> Time for the skin temperatures. Skin temperature about 36.5° nearly as high as the rectal temperature. [Applause] >> The metabolic rate, a measure of the total heat production of the cells, is computed from the amount of oxygen consumed and is measured in kilo calories per hour. >> Very good recording. >> At rest, this man's heat production is about 60 kilo calories. The man is continually losing heat to the cooler room. But even while resting, he is producing enough heat to replace all the heat is losing. Now the room will be cooled. Even after being in the cold for over 2 hours, this man's internal temperature has climbed a fraction of a degree. The additional heat is the result of shivering, an involuntary increase in the work of muscle cells. More cellular work, more heat production. This is the body's only way of producing heat to offset heat losses. While the internal temperature remained nearly constant, however, skin temperature has dropped sharply, especially in the arms and legs. It's as though the body were trying to keep a constant temperature inside the trunk where the vital organs are while allowing the extremities to get cold. The temperature changes in the extremities are directly related to the amount of blood flowing in them. Circulating through the open vessels, warm blood from deep inside the body conveys heat to the extremities. If the air temperature drops, many vessels in the extremities constrict. Less blood flow near the skin, less heat loss from the body. Control of blood flow in the extremities is of vital importance to animals which live in cold regions such as the Arctic wolf. This sensor measures the temperature of the wolf's unprotected foot pad. In this experiment, the animals foot will be immersed in a bath of antifreeze to simulate the conditions of the Arctic winter well below the freezing point of the cells. The bath is cooled by dry ice >> is minus 34. >> Okay, back to the foot. >> You ready to dip? >> Yeah. >> Okay, let's dip. Go. The animal is losing heat very rapidly to the cold bath leveling out at zero. >> Yet within seconds, the foot temperature levels off just above freezing and remains there indefinitely. Rather than constricting the blood vessels, the wolf has pumped more warm blood from the trunk to the foot to keep it from freezing. The animal is controlling its blood flow so precisely that only the exact amount of blood needed to keep the foot from freezing is allowed to leave the trunk in cold environments. Then animals can use two physiological mechanisms to adjust to heat losses. One is to control blood flow by constricting blood vessels near the body surface. Animals keep heat within the trunk. By dilating the vessels, many animals exposed to extreme cold keep unprotected parts of the body from freezing. The other mechanism is to increase metabolism, producing more heat. The result is a constant internal temperature. In some situations though, the body must get rid of excess heat. Excess heat presents a particular problem because a rise in body temperature of only a few degrees will seriously disrupt biochemical reactions. We have a rectal reading. >> Thank you. Good recording. Now >> turn the treadmill on. Exercise, an increase in cellular work, produces excess heat. In response, blood vessels dilate to increase blood flow to the skin from where heat can be lost to the environment. But since the room is warmer than the body, the blood picks up heat. Body temperature rises. So to balance heat gain with heat loss. The body activates another mechanism, sweating. Sweat evaporates quickly in low humidity, cooling the skin and thereby the blood flowing near the skin. So even though this man continues to produce heat at a high rate, his internal temperature has stabilized at a safe level. The situation is different when the air is very humid. In a humid environment, sweat cannot evaporate efficiently. Evaporative cooling is ineffective. Under these conditions, the body's mechanisms are unable to keep the internal temperature from rising to a dangerous level. Time to stop. Jim, >> can you get that switch, please? >> Very good. Usually, however, the temperature within the trunk fluctuates less than one degree. The main heat control center, the body's thermostat, so to speak, is located in the hypothalamus near the base of the brain. The function of the hypothalamus in regulating body temperature, can be shown with the help of a specially prepared animal. The temperature of the hypothalamus is measured through the sealed tubing implanted in the head. Water circulating through the tubing can be warmed or cooled to simulate the flow of warm or cool blood through the hypothalamus. The normal temperature of the hypothalamus is about 38.6° 6° centigrade. Room temperature is about 25°. The animal is resting comfortably. First, the hypothalamus will be warmed. Even though room temperature remains constant, warming the hypothalamus causes the dog to pant, the typical response to heat in many animals. Now the hypothalamus will be cooled. All other conditions will remain the same. Cooling the hypothalamus causes the animal to shiver. Evidently, there's a narrow temperature range which the body considers normal and within which no observable adjustments are made. But if this range is exceeded, the hypothalamus senses the change and triggers an appropriate response. The greater the change, the more intense the response. To adjust to the wide variety of conditions in which the body may find itself, the hypothalamus can reset its neutral temperature range. Higher as in a cold environment or during a fever, or lower as when exercising. This in turn triggers the body's responses at a higher or lower temperature. Thus, the hypothalamus has the flexibility needed to achieve a delicate balance that enables the body to function normally under a wide variety of conditions. The capability to maintain a high body temperature represents one of the supreme achievements in the evolution of life. Only animals with this capability can overcome the heating and chilling effects of their immediate environment and so can maintain peak physical and mental efficiency virtually at all times. It can be truly said of these animals that though it be winter outside, the fire of life burns steadfast within. [Music] [Music]