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18/04/12 Regula=ng and Conforming • A regulator uses internal control mechanisms to moderate internal change in the face of external, environmental fluctua=on • A conformer allows its internal condi=on to vary with certain external changes • Animals may regulate some environmental variables while conforming to others © 2011 Pearson Education, Inc. Figure 40.7 Homeostasis • Organisms use homeostasis to maintain a steady state or internal balance regardless of external environment • In humans, body temperature, blood pH, and glucose concentra=on are each maintained at a constant level © 2011 Pearson Education, Inc. 1 18/04/12 Mechanisms of Homeostasis • Mechanisms of homeostasis moderate changes in the internal environment • For a given variable, fluctua=ons above or below a set point serve as a s2mulus; these are detected by a sensor and trigger a response • The response returns the variable to the set point Anima=on: Nega=ve Feedback Anima=on: Posi=ve Feedback © 2011 Pearson Education, Inc. Figure 40.8 Feedback Control in Homeostasis • The dynamic equilibrium of homeostasis is maintained by nega2ve feedback, which helps to return a variable to a normal range • Most homeosta=c control systems func=on by nega=ve feedback, where buildup of the end product shuts the system off • Posi2ve feedback amplifies a s=mulus and does not usually contribute to homeostasis in animals © 2011 Pearson Education, Inc. 2 18/04/12 Altera7ons in Homeostasis • Set points and normal ranges can change with age or show cyclic varia=on • In animals and plants, a circadian rhythm governs physiological changes that occur roughly every 24 hours © 2011 Pearson Education, Inc. Figure 40.9 Figure 40.9a 3 18/04/12 Figure 40.9b • Homeostasis can adjust to changes in external environment, a process called acclima2za2on © 2011 Pearson Education, Inc. Concept 40.3: Homeosta=c processes for thermoregula=on involve form, func=on, and behavior • Thermoregula2on is the process by which animals maintain an internal temperature within a tolerable range © 2011 Pearson Education, Inc. 4 18/04/12 Endothermy and Ectothermy • Endothermic animals generate heat by metabolism; birds and mammals are endotherms • Ectothermic animals gain heat from external sources; ectotherms include most invertebrates, fishes, amphibians, and nonavian rep=les © 2011 Pearson Education, Inc. • In general, ectotherms tolerate greater varia=on in internal temperature, while endotherms are ac=ve at a greater range of external temperatures • Endothermy is more energe=cally expensive than ectothermy © 2011 Pearson Education, Inc. Figure 40.10 5 18/04/12 Varia=on in Body Temperature • The body temperature of a poikilotherm varies with its environment • The body temperature of a homeotherm is rela=vely constant • The rela=onship between heat source and body temperature is not fixed (that is, not all poikilotherms are ectotherms) © 2011 Pearson Education, Inc. Balancing Heat Loss and Gain • Organisms exchange heat by four physical processes: radia=on, evapora=on, convec=on, and conduc=on © 2011 Pearson Education, Inc. Figure 40.11 6 18/04/12 • Heat regula=on in mammals o`en involves the integumentary system: skin, hair, and nails • Five adapta=ons help animals thermoregulate: – Insula=on – Circulatory adapta=ons – Cooling by evapora=ve heat loss – Behavioral responses – Adjus=ng metabolic heat produc=on © 2011 Pearson Education, Inc. Insula7on • Insula=on is a major thermoregulatory adapta=on in mammals and birds • Skin, feathers, fur, and blubber reduce heat flow between an animal and its environment • Insula=on is especially important in marine mammals such as whales and walruses © 2011 Pearson Education, Inc. Circulatory Adapta7ons • Regula=on of blood flow near the body surface significantly affects thermoregula=on • Many endotherms and some ectotherms can alter the amount of blood flowing between the body core and the skin • In vasodila=on, blood flow in the skin increases, facilita=ng heat loss • In vasoconstric=on, blood flow in the skin decreases, lowering heat loss © 2011 Pearson Education, Inc. 7 18/04/12 • The arrangement of blood vessels in many marine mammals and birds allows for countercurrent exchange • Countercurrent heat exchangers transfer heat between fluids flowing in opposite direc=ons and reduce heat loss © 2011 Pearson Education, Inc. Figure 40.12 • Some bony fishes and sharks also use countercurrent heat exchanges • Many endothermic insects have countercurrent heat exchangers that help maintain a high temperature in the thorax © 2011 Pearson Education, Inc. 8 18/04/12 Cooling by Evapora7ve Heat Loss • Many types of animals lose heat through evapora=on of water from their skin • Pan=ng increases the cooling effect in birds and many mammals • Swea=ng or bathing moistens the skin, helping to cool an animal down © 2011 Pearson Education, Inc. Behavioral Responses • Both endotherms and ectotherms use behavioral responses to control body temperature • Some terrestrial invertebrates have postures that minimize or maximize absorp=on of solar heat © 2011 Pearson Education, Inc. Figure 40.13 9 18/04/12 Adjus7ng Metabolic Heat Produc7on • Thermogenesis is the adjustment of metabolic heat produc=on to maintain body temperature • Thermogenesis is increased by muscle ac=vity such as moving or shivering • Nonshivering thermogenesis takes place when hormones cause mitochondria to increase their metabolic ac=vity • Some ectotherms can also shiver to increase body temperature © 2011 Pearson Education, Inc. Figure 40.14 Figure 40.15 10 18/04/12 Acclima=za=on in Thermoregula=on • Birds and mammals can vary their insula=on to acclima=ze to seasonal temperature changes • When temperatures are subzero, some ectotherms produce an=freeze compounds to prevent ice forma=on in their cells © 2011 Pearson Education, Inc. Physiological Thermostats and Fever • Thermoregula=on is controlled by a region of the brain called the hypothalamus • The hypothalamus triggers heat loss or heat genera=ng mechanisms • Fever is the result of a change to the set point for a biological thermostat © 2011 Pearson Education, Inc. Figure 40.16 11 18/04/12 Figure 40.16a Figure 40.16b Concept 40.4: Energy requirements are related to animal size, ac=vity, and environment • Bioenerge2cs is the overall flow and transforma=on of energy in an animal • It determines how much food an animal needs and it relates to an animal s size, ac=vity, and environment © 2011 Pearson Education, Inc. 12 18/04/12 Energy Alloca=on and Use • Animals harvest chemical energy from food • Energy-‐containing molecules from food are usually used to make ATP, which powers cellular work • A`er the needs of staying alive are met, remaining food molecules can be used in biosynthesis • Biosynthesis includes body growth and repair, synthesis of storage material such as fat, and produc=on of gametes © 2011 Pearson Education, Inc. Figure 40.17 Quan=fying Energy Use • Metabolic rate is the amount of energy an animal uses in a unit of =me • Metabolic rate can be determined by – An animal s heat loss – The amount of oxygen consumed or carbon dioxide produced © 2011 Pearson Education, Inc. 13 18/04/12 Figure 40.18 Minimum Metabolic Rate and Thermoregula=on • Basal metabolic rate (BMR) is the metabolic rate of an endotherm at rest at a comfortable temperature • Standard metabolic rate (SMR) is the metabolic rate of an ectotherm at rest at a specific temperature • Both rates assume a nongrowing, fas=ng, and nonstressed animal • Ectotherms have much lower metabolic rates than endotherms of a comparable size © 2011 Pearson Education, Inc. Influences on Metabolic Rate • Metabolic rates are affected by many factors besides whether an animal is an endotherm or ectotherm • Two of these factors are size and ac=vity © 2011 Pearson Education, Inc. 14 18/04/12 Size and Metabolic Rate • Metabolic rate is propor=onal to body mass to the power of three quarters (m3/4) • Smaller animals have higher metabolic rates per gram than larger animals • The higher metabolic rate of smaller animals leads to a higher oxygen delivery rate, breathing rate, heart rate, and greater (rela=ve) blood volume, compared with a larger animal © 2011 Pearson Education, Inc. Figure 40.19 Figure 40.19a 15 18/04/12 Figure 40.19b Ac7vity and Metabolic Rate • Ac=vity greatly affects metabolic rate for endotherms and ectotherms • In general, the maximum metabolic rate an animal can sustain is inversely related to the dura=on of the ac=vity © 2011 Pearson Education, Inc. Energy Budgets • Different species use energy and materials in food in different ways, depending on their environment • Use of energy is par==oned to BMR (or SMR), ac=vity, thermoregula=on, growth, and reproduc=on © 2011 Pearson Education, Inc. 16 18/04/12 Figure 40.20 Figure 40.20a Figure 40.20b 17 18/04/12 Torpor and Energy Conserva=on • Torpor is a physiological state in which ac=vity is low and metabolism decreases • Torpor enables animals to save energy while avoiding difficult and dangerous condi=ons • Hiberna2on is long-‐term torpor that is an adapta=on to winter cold and food scarcity © 2011 Pearson Education, Inc. Figure 40.21 • Summer torpor, called es=va=on, enables animals to survive long periods of high temperatures and scarce water • Daily torpor is exhibited by many small mammals and birds and seems adapted to feeding paierns © 2011 Pearson Education, Inc. 18 18/04/12 Figure 40.UN01 19