Internal Regulation PDF

Internal Regulation Chapter 9 W hat is life? You could define life in many ways depending on whether...

Internal Regulation Chapter 9 W hat is life? You could define life in many ways depending on whether your purpose is medical, legal, philosophical, or poetic. Biologically, the necessary condition for life is a coordinated set of chemical reactions. Chapter Outline Module 9.1 Temperature Regulation Homeostasis and Allostasis Controlling Body Temperature Not all chemical reactions are alive, but all life has well-regulated chemical In Closing: Combining Physiological and reactions. Behavioral Mechanisms Module 9.2 Every chemical reaction in a living body takes place in a water solution at Thirst Mechanisms of Water Regulation a rate that depends on the types of molecules, their concentration, and their Osmotic Thirst temperature. Our behavior is organized to keep the right chemicals in the Hypovolemic Thirst and Sodium-Specific Hunger right proportions and at the right temperature. In Closing: The Psychology and Biology of Thirst Module 9.3 Hunger Digestion and Food Selection Short- and Long-Term Regulation of Feeding Brain Mechanisms Eating Disorders In Closing: The Multiple Controls of Hunger Learning Objectives After studying this chapter, you should be able to: 1. List examples of how temperature regula- tion contributes to behaviors. 2. Explain why a constant high body tem- perature is worth all the energy it costs. 3. Describe why a moderate fever is advanta- geous in fighting an infection. 4. Distinguish between osmotic and hypovo- lemic thirst, including the brain mecha- nisms for each. 5. Describe the physiological factors that influence hunger and satiety. Opposite: All life on Earth requires water, and animals drink it wherever they can find it. (© iStock.com/StockPhotoAstur) 289 Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-203 Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.  Module 9.1 Temperature Regulation H ere’s an observation that puzzled biologists for years: The Japanese giant hornet sometimes invades bee colo- When a small male garter snake emerges from hibernation nies, kills one or more bees, and takes them to feed to in early spring, it emits female pheromones for the first day or its larvae. When one of these hornets invades a hive of two. The pheromones attract larger males that swarm all over Japanese honeybees, the bees form a tight swarm of more him, trying to copulate. Presumably, the tendency to release than 500, surrounding the hornet in a tiny ball. Why? The female pheromones must have evolved to provide the small combined body heat of all those bees raises the tempera- male some advantage. But what? Biologists speculated about ture to a level that is lethal to the hornet, but not to the ways in which this pseudo-mating experience might help the bees (Ono, Igarashi, Ohno, & Sasaki, 1995). small male attract real females. The truth is simpler: A male Migratory birds do most of their migratory flying at night. that has just emerged from hibernation is so cold that it has Why? The nights are cooler. A bird flying in midday trouble slithering out of its burrow. The larger males emerged would overheat and frequently have to stop for a drink, from hibernation earlier and already had a chance to warm often in places where fresh water is difficult to find. themselves in a sunny place. When the larger males swarm all over the smaller male, they warm him and increase his activity level (Shine, Phillips, Waye, LeMaster, & Mason, 2001). Here are more examples that temperature regulation helps to explain: Have you ever noticed gulls, ducks, or other large birds standing on one leg (see Figure 9.1)? Why do they do that, when balancing on two legs would seem easier? One reason is to conserve body heat on cold days. By standing on one leg, they protect the heat in the other leg (Ehrlich, Dobkin, & Wheye, 1988). Vultures sometimes defecate onto their own legs. Are they just careless slobs? No. They defecate onto their legs on hot days so that the evaporating excretions will cool their legs (Ehrlich, Dobkin, & Wheye, 1988). For many years, biologists puzzled about the function of toucans’ huge, clumsy bills (see Figure 9.2). The answer is temperature regulation (Tattersall, Andrade, & Abe, 2009). While flying on hot days, a toucan directs more blood flow to the beak, where the passing air cools it. At night the toucan tucks its bill under a wing to prevent undue loss of heat. Most lizards live solitary lives, but Australian thick-tailed geckos sometimes form tight huddles. Why? They live in an environment with rapid temperature fluctuations. They huddle only when the environmental temperature is falling rapidly. By huddling, they increase insulation and Figure 9.1 Why do birds sometimes stand on one foot? prevent a rapid drop in body temperature (Shah, Shine, One reason is that holding one leg next to the body keeps it warm. (F1online digitale Bildagentur GmbH/Alamy Stock Photo) Hudson, & Kearney, 2003). 290 Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-203 Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.  9.1 Temperature Regulation 291 The point is that temperature affects behavior in many ways that we easily overlook. The modules on thirst and hunger, later in this chapter, present further examples of how temper- ature control affects behavior. Homeostasis and Allostasis Physiologist Walter B. Cannon (1929) introduced the term homeostasis (HO-mee-oh-STAY-sis) to refer to tempera- ture regulation and other biological processes that keep hironai/Shutterstock.com body variables within a fixed range. The process resembles the thermostat in a house with heating and cooling systems. Someone sets the minimum and maximum temperatures on the thermostat. When the temperature in the house drops below the minimum, the thermostat triggers the furnace Figure 9.2 Why do toucans have such huge bills? They use their bills to radiate heat when they need to cool the body. to provide heat. When the temperature rises above the They cover the bill at night to decrease heat loss. maximum, the thermostat turns on the air conditioner. For another example, stand and balance on one foot. Whenever your weight happens to shift left, right, forward, or backward, you quickly correct your position to maintain balance. Decades ago, psychologists reported that infant rats Homeostatic processes in animals trigger physiological appeared deficient in certain aspects of learning, eating, and behavioral activities that keep certain variables within a and drinking. Later results showed that the real problem set range. In many cases, the range is so narrow that we refer was temperature control. Researchers generally test ani- to it as a set point, a single value that the body works to main- mals at room temperature, about 208 to 238C (68 to 738F), tain. For example, if calcium is deficient in your diet and its which is comfortable for adult humans but dangerously concentration in the blood begins to fall below the set point cold for an isolated baby rat (see Figure 9.3). Infant rats of 0.16 g/L (grams per liter), storage deposits in your bones that seem incapable of some task in a cold room do much release additional calcium into the blood. If the calcium level better in a warmer room (Satinoff, 1991). in the blood rises above 0.16 g/L, you store part of the excess Certain studies found that female rats learned best dur- in your bones and excrete the rest. Similar mechanisms main- ing their fertile period (estrus), but in other studies, they tain constant blood levels of water, oxygen, glucose, sodium learned best a day or two before their fertile period (pro- chloride, protein, fat, and acidity (Cannon, 1929). Processes estrus). The difference depended on the temperature of that reduce discrepancies from the set point are known as the room. Rats in estrus do better in a cooler environment, negative feedback. Much of motivated behavior can be de- presumably because they are generating so much heat on scribed as negative feedback: Something causes a disturbance, their own. Rats in proestrus do better in a warmer envi- and behavior proceeds until it relieves the disturbance. ronment (Rubinow, Arseneau, Beverly, & Juraska, 2004). However, the concept of homeostasis is not fully satisfac- tory, because the body does not maintain complete constancy. For example, your body temperature is about half a Celsius degree higher in mid-afternoon than in the middle of the night. Most animals maintain a nearly constant body weight from day to day, but add body fat in fall and decrease it in spring. (The increased fat is a good reserve in preparation for probable food shortage during the winter. It also provides insulation against the cold.) We can describe these altera- tions as changes in the set point, but even changes in the set point don’t fully account for many observations. Much of our behavior anticipates a need before it occurs. For example, a sign of danger provokes a sudden increase in heart rate, blood pressure, and sweating, preparing the body for vigorous activ- Figure 9.3 Difficulties of temperature regulation for a newborn ity. Similarly, as the air is starting to warm up, a hiker increases rodent thirst and decreases urine production by the kidneys, antici- A newborn rat has no hair, thin skin, and little body fat. If left exposed to pating probable sweating and dehydration. (Other animals do the cold, it becomes inactive. the same.) To describe these dynamic changes, researchers use (A. Blank/NAS/Science Source) the term allostasis (from the Greek roots meaning “variable” Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-203 Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 292 CHAPTER 9 Internal Regulation and “standing”), which means the adaptive way in which the Mammals and birds are endothermic, meaning that they body anticipates needs depending on the situation, avoid- generate enough body heat to remain significantly above the ing errors rather than just correcting them (McEwen, 2000; temperature of the environment. A synonym is homeothermic, Sterling, 2012). We shall encounter additional examples of al- from Greek roots meaning “same heat.” Endothermic animals use lostasis later in this chapter. Homeostasis and allostasis don’t physiological mechanisms to keep their core temperature nearly work perfectly, of course. If they did, we would not have prob- constant. Endothermy is costly, especially for small animals. lems such as obesity, high blood pressure, or diabetes. An animal generates heat in proportion to its total mass, but it radiates heat in proportion to its surface area. A small mammal or bird, such as a mouse or a hummingbird, has a high surface- STOP & CHECK to-volume ratio and therefore radiates heat rapidly. Such animals need much fuel each day to maintain their body temperature. 1. How does the idea of allostasis differ from homeostasis? To cool ourselves when the air is warmer than body tem- advance to prevent or minimize changes. perature, we have only one physiological mechanism, evapo- ANSWER ration. Humans sweat to expose water for evaporation. For fixed range by reacting to changes. Allostasis acts in 1. Homeostasis keeps certain body variables within a species that don’t sweat, the alternatives are licking them- selves and panting. As water evaporates, it cools the body. However, if the air is humid as well as hot, the moisture does not evaporate. Furthermore, you endanger your health if you Controlling Body Temperature cannot drink enough to replace the water you lose by sweat- ing. If you sweat without drinking, you become dehydrated If you were to list your strongest motivations in life, you might (low on water). You then protect your body water by sweating not think to include temperature regulation, but it has a high less, despite the risk of overheating (Tokizawa et al., 2010). priority biologically. An average young adult expends about Several physiological mechanisms increase your body heat 2600 kilocalories (kcal) per day. Where do you suppose all that in a cold environment. One is shivering. Any muscle contrac- energy goes? It is not to muscle movements or mental activ- tions, such as those of shivering, generate heat. Second, de- ity. Most of it goes to basal metabolism, the energy used to creased blood flow to the skin prevents the blood from cooling maintain a constant body temperature while at rest. Maintain- too much. The consequence is warm internal organs but cold ing your body temperature uses about twice as much energy skin. A third mechanism works well for most mammals, though as all other activities combined (Burton, 1994). We produce not humans: When cold, they fluff out their fur to increase in- that much heat largely by metabolism in brown adipose cells, sulation. (We humans also fluff out our “fur” by erecting the tiny cells that are more like muscle cells than like white fat cells. hairs on our skin—“goose bumps.” That mechanism was more They burn fuel as muscle cells do, but release it directly as heat useful back when our remote ancestors had a fuller coat of fur.) instead of as muscle contractions. We also use behavioral mechanisms, just as ectothermic Amphibians, reptiles, and most fish are ectothermic, animals do. In fact, we prefer to rely on behavior when we can. meaning that they depend on external sources for body The more we regulate our temperature behaviorally, the less heat instead of generating it themselves. A synonym is energy we need to spend physiologically (Refinetti & Carlisle, poikilothermic, from Greek roots meaning “varied heat.” 1986). Finding a cool place on a hot day is much better than An ectothermic animal’s body temperature is nearly the sweating (see Figure 9.4). Finding a warm place on a cold day is same as the temperature of its environment. People often call such animals “cold-blooded,” but they are cold only when the environment is cold. Poikilothermic animals lack physiological mechanisms of temperature regulation such as shivering and sweating, but they can regulate their body temperature behaviorally. A desert lizard moves between sunny areas, shady areas, and burrows to maintain a fairly steady body temperature. However, behavioral methods do not enable animals to maintain the same degree of con- stancy that mammals and birds have. Although nearly all fish, amphibians, and reptiles are ectothermic, a few exceptions to that rule do occur. A few large fish, including sharks and tuna, maintain their core body temperature well above that of the surrounding water most of the time (Bernal, Donley, Shadwick, & Syme, 2005). The tegu lizards of South America, about the size of a large rabbit, increase their metabolism during the mating season, raising Figure 9.4 One way to cope with the heat their body temperature to sometimes 108C above that of the On a hot day, wouldn’t you do the same? (Sun-Journal/Ken Love/AP Images) environment (Tattersall et al., 2016). Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-203 Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.  9.1 Temperature Regulation 293 chemicals at the start of the winter (Liou, Tocilj, Davies, & Jia, 2000). Wood frogs actually do freeze, but they have several mechanisms to reduce the damage. They start by withdrawing most fluid from their organs and blood vessels and storing it in extracellular spaces. Therefore, ice crystals have room to expand when they form, without tearing blood vessels or cells. Also, the frogs have chemicals that cause ice crystals to form gradually, not in chunks. Finally, they have extraordinary blood-clotting capacity that quickly repairs any blood vessels that do rupture (Storey & Storey, 1999). Aaron Lang/USFWS The Advantages of Constant High Body Temperature Figure 9.5 Behavioral regulation of body temperature As mentioned, we spend about two-thirds of our total energy Spectacled eiders pool their body heat to melt holes in the ice of the maintaining body temperature (basal metabolism). An ecto- Arctic Ocean, thereby surviving the winter without migrating. thermic animal, with a much lower level of basal metabolism, needs far less fuel. If we didn’t maintain a constant, high body temperature, we could eat less and spend less effort finding food. Given the substantial costs of maintaining our body much smarter than shivering. Here are a few other behavioral temperature, it must provide an important advantage, or mechanisms of temperature regulation: we would not have evolved these mechanisms. What is that advantage? Put on more clothing or take it off. This human strategy For the answer, think back to the chapter on movement: accomplishes what other mammals accomplish by fluffing As the water gets colder, a fish recruits more and more fast- out or sleeking their fur. twitch muscle fibers to remain active, despite the risk of rapid Become more active to get warmer or less active to avoid fatigue. The same is true for amphibians and reptiles. On a overheating. very cold day, a lizard has to change its defense strategy: If To get warm, huddle with others. If you are waiting at a it ran away from a predator, it would either run more slowly bus stop on a cold day, you might feel shy about suggest- than usual or recruit all of its fast-twitch muscles and fatigue ing to a stranger that you hug each other to keep warm. rapidly. So, instead of running, it tries to fight the predator— Other species have no such inhibitions (see Figure 9.5). an act requiring a briefer burst of activity, though it is often a Emperor penguin chicks huddle together to pool their losing battle (James, 2013). heat, increasing their insulation enough to survive an Birds and mammals keep their bodies warm at all times Antarctic winter. Spectacled eiders (in the duck family) and therefore stay constantly ready for vigorous activity, spend their winters in the Arctic Ocean, which is mostly regardless of the temperature of the air. In other words, we eat covered with ice. When more than 150,000 eiders crowd a great deal to support our high metabolism so that even if the together, they not only keep warm but also melt a big hole weather is cold, we can still run rapidly without great fatigue. in the ice where they can dive for fish (Weidensaul, 1999). Let’s qualify this point, however: On a cold day, you divert blood away from the periphery to protect the internal organs and to avoid losing too much heat to the surrounding air. The Surviving in Extreme Cold result is that your muscles are not quite as warm as usual. A If the atmospheric temperature drops below 08C (328F), you competitive athlete needs to warm up, literally, to increase the maintain your body temperature by shivering, shifting blood muscles’ temperature on a cold day. flow away from the skin, and so forth. However, an ectother- Why did mammals evolve a body temperature of 378C mic animal, which by definition takes the temperature of its (988F) instead of some other value? From the standpoint of environment, is vulnerable. If its body temperature drops muscle activity, we gain an advantage by being as warm as below the freezing point of water, ice crystals form. Because possible. A warmer animal has warmer muscles and therefore water expands when it freezes, ice crystals would tear apart runs faster with less fatigue than a cooler animal. When a rep- blood vessels and cell membranes, killing the animal. tile has a choice of environments at different temperatures, Many amphibians and reptiles avoid that risk by bur- it usually chooses to warm itself to 378 to 388C (988 to 1008F) rowing or finding other sheltered locations. However, some (Wagner & Gleeson, 1997). frogs, fish, and insects survive through winters in northern If warmer is better, why not heat ourselves to an even Canada where even the underground temperature approaches higher temperature? First, maintaining a higher temperature –408 C (which is also –408 F). How do they do it? Some insects requires more fuel and energy. Second, and more importantly, and fish stock their blood with glycerol and other antifreeze beyond about 418C (1058F), proteins begin to break their Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-203 Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 294 CHAPTER 9 Internal Regulation bonds and lose their useful properties. Birds’ body tempera- tures are in fact about 418C. STOP & CHECK It is possible to evolve proteins that are stable at higher 2. What is the primary advantage of maintaining a constant temperatures; indeed, odd microscopic animals called ther- high body temperature? mophiles survive in boiling water. However, to do so, they need 3. Why did mammals evolve a temperature of 378C (988F) many extra chemical bonds to stabilize their proteins. The instead of some other temperature? enzymatic properties of a protein depend on its flexibility, so above 378C (988F). making proteins rigid enough to withstand high temperatures ANSWERS However, proteins lose stability at temperatures much makes them inactive at more moderate temperatures (Feller, warm as possible and therefore as fast as possible. 2010). In short, our body temperature of 378C is a trade-off weather. 3. Animals gain an advantage in being as between the advantages of high temperature for rapid move- ready for rapid, prolonged muscle activity even in cold ment and the disadvantages of high temperature for protein 2. A constant high body temperature keeps an animal stability and energy expenditure. Reproductive cells require a cooler environment than the rest of the body (Rommel, Pabst, & McLellan, 1998). Birds lay eggs and sit on them, instead of developing them internally, Brain Mechanisms because the birds’ internal temperature is too hot for an em- bryo. Similarly, in most male mammals, the scrotum hangs The physiological changes that regulate body temperature— outside the body, because sperm production requires a cooler such as shivering, sweating, and changes in blood flow to temperature than the rest of the body. (It’s not just for decora- the skin—depend on areas in and near the hypothalamus tion.) A man who wears his undershorts too tight keeps his (see Figure 9.6), especially the anterior hypothalamus and testes too close to the body, overheats them, and produces the preoptic area, located just anterior to the anterior hypo- fewer healthy sperm cells. Pregnant women are advised to thalamus. (It is called preoptic because it is near the optic avoid hot baths and anything else that might overheat a chiasm, where the optic nerves cross.) Because of the close developing fetus. relationship between the preoptic area and the anterior Third Anterior ventricle commissure Pineal body Hypothalamus Mamillary Pituitary body Paraventricular nucleus Dorsal of hypothalamus hypothalamus Anterior commissure Lateral hypothalamus Dorsomedial (behind plane of view) hypothalamus Posterior hypothalamus Anterior hypothalamus Preoptic area Suprachiasmatic Mamillary body nucleus Ventromedial Arcuate nucleus Optic chiasm hypothalamus Figure 9.6 Major subdivi- sions of the hypothalamus and pituitary Anterior pituitary Posterior (Based on Nieuwenhuys, Voogd, & pituitary vanHuijzen, 1988) Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-203 Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.  9.1 Temperature Regulation 295 Temperature receptors in skin Figure 9.7 Integration of temperature information by the POA/AH Control of shivering, If the brain and skin are overheated, the POA/AH sweating, heart rate, sends signals that lead to sweating and other meth- Temperature receptors POA/AH blood flow to skin, ods of heat loss. If the brain and skin are cooled, or if in brain and other organs metabolism in brown adipose tissue, etc. prostaglandins and histamine indicate an infection, the POA/AH initiates shivering, increased heart rate, decreased blood flow to the skin, and increased Immune Prostaglandins metabolism by brown adipose tissue. Infection response and histamine hypothalamus, researchers often treat them as a single area, Fever the preoptic area/anterior hypothalamus, or POA/AH. The POA/AH and a couple other hypothalamic areas send output A fever represents an increased set point for body tempera- to the hindbrain’s raphe nucleus, which controls the auto- ture. Just as you shiver or sweat when your body temperature nomic responses such as shivering, sweating, changes in heart goes below or above its usual 378C, when you have a fever of, rate and metabolism, and changes in blood flow to the skin say, 398C (1028F), you shiver or sweat whenever your tem- (Morrison, 2016; Yoshida, Li, Cano, Lazarus, & Saper, 2009). perature deviates from that level. In other words, fever is The POA/AH integrates several types of information not something an infection does to the body; it is something (Nakamura, 2011). It receives input from temperature receptors the hypothalamus directs the body to produce. Moving to a in the skin, in the organs, and in the hypothalamus (Song et al., cooler room does not lower your fever. Your body just works 2016). If either the skin or the hypothalamus is hot, an animal harder to keep its temperature at the feverish level. sweats or pants vigorously and seeks a cooler location. If either Because newborn rabbits have an immature hypothal- is cold, the animal shivers and seeks a warmer location. The amus, they do not shiver in response to infections. If they animal reacts most vigorously if the skin and hypothalamus are are given a choice of environments, however, they select both hot or both cold. The POA/AH also receives input from a spot warm enough to raise their body temperature and the immune system, which reacts to an infection by sending produce a fever by behavioral means (Satinoff, McEwen, & prostaglandins and histamines to the POA/AH (Ek et al., 2001; Williams, 1976). Fish and reptiles with an infection also Leon, 2002; Tabarean, Sanchez-Alavez, & Sethi, 2012). Those choose a warm enough environment, if they can find one, chemicals are the cause of shivering, increased metabolism, and to produce a feverish body temperature (Kluger, 1991). other processes that produce a fever. People lacking the appro- Again, the point is that fever is something the animal does priate receptors for those chemicals fail to develop a fever, even to fight an infection. when they have pneumonia or similar diseases (Hanada et al., Does fever do any good? Certain types of bacteria grow 2009). Figure 9.7 summarizes the role of the POA/AH. less vigorously at high temperatures than at normal mam- The POA/AH is not the only brain area that detects tem- malian body temperatures. Also, the immune system works perature, but it is the primary area for controlling physiological more vigorously at an increased temperature (Skitzki, Chen, mechanisms of temperature regulation such as sweating or Wang, & Evans, 2007). Other things being equal, develop- shivering. After damage to the POA/AH, mammals can still ing a moderate fever increases an individual’s chance of regulate body temperature, but less efficiently. They also use surviving a bacterial infection (Kluger, 1991). However, a fe- the behavioral mechanisms that a lizard might use, such as ver above about 398C (1038F) in humans does more harm seeking a warmer or colder location (Satinoff & Rutstein, than good, and a fever above 418C (1098F) is life-threatening 1970; Van Zoeren & Stricker, 1977). (Rommel, Pabst, & McLellan, 1998). STOP & CHECK 4. What are the sources of input to the POA/AH? 5. If you had damage to your POA/AH, what would happen to STOP & CHECK your body temperature? 6. What evidence indicates that fever is an adaptation to fight illness? to your normal temperature. ANSWERS try to find a place in the environment that keeps you close surviving a bacterial infection. that control body temperature. However, you could still ANSWER its bacterial growth and increases the probability of shiver, sweat, or control other physiological mechanisms a feverish level. Furthermore, a moderate fever inhib- detects an infection. 5. You would be much less able to use behavioral means to raise their temperature to prostaglandins and histamines when the immune system fish, reptiles, and immature mammals with infections skin, the organs, and the hypothalamus. It also receives elevated temperature at a nearly constant level. Also, 4. The POA/AH receives input from temperatures in the 6. The body will shiver or sweat to maintain its Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-203 Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 296 CHAPTER 9 Internal Regulation Module 9.1 In Closing Combining Physiological and Behavioral Mechanisms Physiological mechanisms and behavioral mechanisms work mechanism fails, another mechanism comes to your rescue. It together. Your body has physiological mechanisms to maintain is not, however, a true redundancy in the sense of two mecha- constant body temperature, including shivering, sweating, and nisms doing exactly the same thing. Each of your mechanisms changes in blood flow. You also rely on behavioral mechanisms, of temperature regulation solves an aspect of the problem in a such as finding a cooler or warmer place, adding or removing different way. We shall see this theme again in the discussions clothing, and so forth. Redundancy reduces your risk: If one of thirst and hunger. Summary 1. It is easy to overlook the importance of temperature regu- needed to maintain body temperature. Mammalian body lation. Many seemingly odd animal behaviors make sense temperature of 378C is a compromise between these com- as ways to heat or cool the body. 290 peting considerations. 293 2. Homeostasis is a tendency to maintain a body variable 5. The preoptic area and anterior hypothalamus (POA/AH) near a set point. Temperature, hunger, and thirst are are critical for temperature control. Cells there moni- almost homeostatic, but the set point changes in varying tor both their own temperature and that of the skin and circumstances. 291 organs. When they receive input indicating an infection, 3. A high body temperature enables a mammal or bird to they initiate responses that produce a fever. 294 move rapidly without excessive fatigue even in a cold 6. All animals rely partly on behavioral mechanisms for environment. 293 temperature regulation. 295 4. From the standpoint of muscle activity, the higher the 7. A moderate fever helps an animal combat an body temperature, the better. However, as temperatures infection. 295 increase, protein stability decreases, and more energy is Key Terms Terms are defined in the module on the page number indi- page 589. Interactive flash cards, audio reviews, and crossword cated. They are also presented in alphabetical order with defi- puzzles are among the online resources available to help you nitions in the book’s Subject Index/Glossary, which begins on learn these terms and the concepts they represent. allostasis 291 endothermic 292 preoptic area/anterior hypothala- basal metabolism 292 homeostasis 291 mus (POA/AH) 295 ectothermic 292 negative feedback 291 set point 291 Thought Question Speculate on why birds have higher body temperatures than mammals. Module 9.1 End of Module Quiz 1. What is meant by allostasis? A. Processes that react to any change to bring the body C. Random changes in the internal processes of the body back to equilibrium D. The ideal levels of all body variables B. Processes that anticipate future needs 2. Well over half of the human body’s energy is devoted to which of the following? A. Basal metabolism C. Brain activity B. Muscle contractions D. Keeping the heart going Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-203 Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.  9.1 Temperature Regulation 297 3. How do ectothermic animals regulate their body temperature, if at all? A. They move to a location with a more favorable C. They increase their metabolic rate. temperature. D. They do not regulate their body temperature at all. B. They use physiological mechanisms such as shivering and sweating. 4. Which of the following is an ectothermic animal? A. Penguin C. Mouse B. Human D. Snake 5. What is the primary advantage of maintaining a constant high body temperature? A. It saves us the energy from having to look for a com- C. It enables the digestive system to process a greater fortable temperature. variety of nutrients. B. It keeps the muscles ready for rapid, prolonged activity D. It enables us to survive in warmer climates. even in cold weather. 6. If we inserted a probe into your POA/AH and heated it, what would happen? A. You would sweat. C. You would seek a warmer environment. B. You would shiver. D. Your skin receptors sensitive to temperature would become more sensitive. 7. When you have an infection, what causes the fever? A. The infective agent stimulates the heart to beat faster. C. The immune system delivers prostaglandins and his- B. The infective agent impairs the activity of the tamine to the hypothalamus. hypothalamus. D. The immune system decreases blood flow to the brain. 8. Which of the following is the most correct description of a fever? A. Fever is one way in which the body fights against C. Fever indicates that the POA/AH is not functioning bacteria. properly. B. Fever is one way in which bacteria cause damage to D. Fever is a result of synchrony between the heart and the body. the lungs. Answers: 1B, 2A, 3A, 4D, 5B, 6A, 7C, 8A. Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-203 Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.  Module 9.2 Thirst W ater constitutes about 70 percent of the mammalian body. Because the concentration of chemicals in water determines the rate of all chemical reactions in the body, you STOP & CHECK 7. If you lacked vasopressin, would you drink like a beaver or like need to maintain the water in your body within narrow limits. a gerbil? Why? The body also needs enough fluid in the circulatory system to maintain normal blood pressure. You could survive for days, would need to drink an equal amount to replace it. ANSWER more like a beaver. You would excrete much fluid, so you maybe weeks, without food, but not long without water. 7. If you lacked vasopressin, you would have to drink Mechanisms of Water Regulation Species differ in their strategies for maintaining water. Beavers and other animals that live in rivers or lakes drink plenty of Osmotic Thirst water, eat moist foods, and excrete dilute urine. In contrast, We distinguish two types of thirst. Eating salty foods causes most gerbils and other desert animals go through life without osmotic thirst, and losing fluid by bleeding or sweating drinking at all. They gain water from their food and they have induces hypovolemic thirst. many adaptations to avoid losing water, including the ability The combined concentration of all solutes (molecules in to excrete dry feces and concentrated urine. Unable to sweat, solution) in mammalian body fluids remains at a nearly con- they avoid the heat of the day by burrowing under the ground. stant level of 0.15 M (molar). (Molarity is a measure of the Their highly convoluted nasal passages minimize water loss number of particles per unit of solution, regardless of the size when they exhale. of each particle. A 1.0 M solution of sugar and a 1.0 M solution We humans vary our strategy depending on circum- of sodium chloride have the same number of molecules per stances. If you cannot find enough to drink or if the water tastes liter.) This fixed concentration of solutes is a set point, simi- bad, you conserve water by excreting more concentrated urine lar to the set point for temperature. Any deviation activates and decreasing your sweat, somewhat like a gerbil, although not mechanisms that restore the concentration of solutes to the to the same extreme. Your posterior pituitary (see Figure 9.6) set point. releases the hormone vasopressin that raises blood pressure by Osmotic pressure is the tendency of water to flow across constricting blood vessels. (The term vasopressin comes from a semipermeable membrane from the area of low solute con- vascular pressure.) The increased pressure helps compensate centration to the area of higher concentration. A semiper- for the decreased blood volume. Vasopressin is also known as meable membrane is one through which water can pass but antidiuretic hormone (ADH) because it enables the kidneys solutes cannot. The membrane surrounding a cell is almost a to reabsorb water from urine and therefore make the urine semipermeable membrane because water flows across it freely more concentrated. (Diuresis means “urination.”) You also in- and various solutes flow either slowly or not at all between crease your secretion of vasopressin while sleeping so that you the intracellular fluid inside the cell and the extracellular fluid can preserve your body water while you cannot drink (Trudel & outside it. Osmotic pressure occurs when solutes are more Bourque, 2010). Vasopressin helps you get through the night concentrated on one side of the membrane than on the other. without going to the toilet. If you eat something salty, sodium ions spread through In most cases, our strategy is closer to that of beavers: We the blood and the extracellular fluid but do not cross the drink more than we need and excrete the excess. (However, if membranes into cells. The result is a higher concentration of you drink extensively without eating, as many alcoholics do, solutes (including sodium) outside the cells than inside. The you may excrete enough body salts to harm yourself.) Most resulting osmotic pressure draws water from the cells into the of our drinking is with meals or in social situations, and most extracellular fluid. Certain neurons detect their own loss of people seldom experience intense thirst. water and then trigger osmotic thirst, a drive for water that 298 Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-203 Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.  9.2 Thirst 299 (a) Greater concentration of (b) Water flows out of the solutes (green dots) outside cell, equalizing the solute the cell than inside. concentration and shrinking the cell. Figure 9.8 The consequence of a dif- ference in osmotic pressure (a) Suppose a solute such as NaCl is more concentrated outside the cell than inside. (b) Water flows by osmosis out of the cell until the concentrations are equal. Neurons in certain brain areas detect their own dehydration and trigger thirst. helps restore the normal state (see Figure 9.8). The kidneys in the digestive tract, enabling it to anticipate an osmotic need also excrete more concentrated urine to rid the body of excess before the rest of the body experiences it (Bourque, 2008). sodium and maintain as much water as possible. The brain areas surrounding the third ventricle are in How does the brain detect osmotic pressure? It a good position to monitor the contents of the blood, be- has receptors around the third ventricle, including the cause the blood–brain barrier is weak in this area, enabling OVLT (organum vasculosum laminae terminalis) and the chemicals to enter that would not reach neurons elsewhere subfornical organ (SFO) (Hiyama, Watanabe, Okado, & Noda, in the brain. The danger, of course, is that a weak blood– 2004) (see Figure 9.9). Those receptors detect osmotic pres- brain barrier exposes neurons to potential harm. At least sure and the sodium content of the blood (Tiruneh, Huang, & in mice, new neurons form in this area, replacing ones that Leenen, 2013). The OVLT also receives input from receptors may have died (Hourai & Miyata, 2013). Other species have not yet been tested. The subfornical organ has one population of neurons that increases thirst and another population that suppresses it (Abbott, Machado, Geerling, & Saper, 2016; Oka, Ye, & Zuker, 2015). Those axons combine with input from the OVLT, the stomach, and elsewhere to provide input to the hypothala- mus. The lateral preoptic area and surrounding parts of the hypothalamus control drinking (Saad, Luiz, Camargo, Renzi, & Manani, 1996). The supraoptic nucleus and the paraventricular nucleus (PVN) control the rate at which the posterior pituitary releases vasopressin. All of this is true, so far as it goes: When your cells start to become dehydrated, they stimulate osmotic thirst. However, Subfornical organ remember the concept of allostasis: Your body does not just react to needs, but also it anticipates needs. For example, when you eat a meal, especially a salty meal, your cells are going to OVLT Third ventricle need water, but you drink at once instead of waiting until your osmotic pressure changes. Also, as a study with mice showed, shortly before time to go to sleep, the body’s circadian rhythm triggers increased secretion of vasopressin, which inhibits the Figure 9.9 The brain’s receptors for osmotic pressure and blood need to urinate and therefore helps retain water when drink- volume ing cannot occur. At the same time, vasopressin stimulates These neurons are in areas surrounding the third ventricle of the brain, thirst (Gizowki, Zaelzer, & Bourque, 2016). That is why you where no blood–brain barrier prevents blood-borne chemicals from often feel an urge to drink something shortly before going entering the brain. to sleep, even if your cells’ osmotic pressure is quite normal (Based in part on DeArmond, Fusco, & Dewey, 1974; Weindl, 1973) at the time. Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-203 Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 300 CHAPTER 9 Internal Regulation When you are thirsty, how do you know when to stop angiotensinogen, a large protein in the blood, to form angio- drinking? You do not continue drinking while the digestive tensin I, which other enzymes convert to angiotensin II. Like system absorbs the water and then the circulatory system vasopressin, angiotensin II constricts the blood vessels, com- pumps it to the hypothalamus. That process takes 15 minutes pensating for the drop in blood pressure (see Figure 9.10). or more, and if you continued drinking for that long, you would Angiotensin II also helps trigger thirst, in conjunction drink far more than you need. Again, allostasis to the rescue: with receptors that detect blood pressure in the large veins. Not only do you start when you anticipate a future need, but However, this thirst is different from osmotic thirst, because also you stop drinking when you anticipate that you have ful- you need to restore lost salts and not just water. This kind of filled a need. Researchers recording activity from mouse brains thirst is known as hypovolemic (HI-po-vo-LEE-mik) thirst, found that one minute of drinking suppressed the activity of meaning thirst based on low volume. When angiotensin II thirst-sensitive neurons in the subfornical organ, long before reaches the brain, it stimulates neurons in areas adjoining the water reached the blood, much less the brain (Zimmerman third ventricle (Fitts, Starbuck, & Ruhf, 2000; Mangiapane & et al., 2016). Cooling the tongue also suppressed activity in Simpson, 1980; Tanaka et al., 2001). Those neurons send ax- the subfornical organ. Thus we may conclude that drinking ons to the hypothalamus, where they release angiotensin II as can serve two purposes, the need for water and the need for