Endotherm vs Ectotherm

12 Key excerpts on "Endotherm vs Ectotherm"

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  eBook - ePub

  Ecology

  From Individuals to Ecosystems

  • Michael Begon, Colin R. Townsend(Authors)
  • 2020(Publication Date)
  • Wiley

    (Publisher)

  But this distinction is not entirely clear‐cut. As we have noted, apart from birds and mammals, there are also other taxa that use heat generated in their own bodies to regulate body temperature, but only for limited periods; and there are some birds and mammals that relax or suspend their endothermic abilities at the most extreme temperatures. In particular, many endothermic animals escape from some of the costs of endothermy by hibernating during the coldest seasons: at these times they behave almost like ectotherms. endotherms: temperature regulation – but at a cost Birds and mammals usually maintain a constant body temperature between 35 and 42°C, and they therefore tend to lose heat in most environments; but this loss is moderated by insulation in the form of fur, feathers and fat, and by controlling blood flow near the skin surface. When it is necessary to increase the rate of heat loss, this too can be achieved by the control of surface blood flow and by a number of other mechanisms shared with ectotherms like panting and the simple choice of an appropriate habitat. Together, all these mechanisms and properties give endotherms a powerful (but not perfect) capability for regulating their body temperature, and the benefit they obtain from this is a constancy of near‐optimal performance. But the price they pay is a large expenditure of energy (Figure 2.12), and thus a correspondingly large requirement for food to provide that energy. Over a certain temperature range (the thermoneutral zone) an endotherm consumes energy at a basal rate. But at environmental temperatures further and further above or below that zone, the endotherm consumes more and more energy in maintaining a constant body temperature

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  Contributions to Thermal Physiology

  Satellite Symposium of the 28th International Congress of Physiological Sciences, Pécs, Hungary, 1980

  • Z. Szelényi, M. Székely(Authors)
  • 2013(Publication Date)
  • Pergamon

    (Publisher)

  Phylogenic aspects of temperature regulation Passage contains an image

  EVOLUTION FROM ECTOTHERMIA TOWARDS ENDOTHERMIA

  A.J. HULBERT,     Department of Biology, University of Wollongong, Wollongong, N.S.W., Australia, 2500

  Publisher Summary

  This chapter discusses the evolution from ectothermia toward endothermia. Many reptiles have been shown to possess a rate of heating different to their rate of cooling. It has been shown in a variety of lizards that vasomotor control of blood flow is a significant contributor to this difference between rates of heating and cooling. This has also been demonstrated in the tuatara and in turtles. Measurement of local cutaneous blood flow in a lizard has shown it to increase during heating. In view of the variety of reptiles in which it has been reported, it seems almost certain that the pre-mammalian reptiles possessed this vasomotor ability to alter their body conductance. Endotherms have a high level of metabolism compared to ectotherms. The resting mammal that is undergoing no extra expenditure of energy for thermoregulation will have a level of energy metabolism that is four to five times that of a similar sized resting reptile that is at the same body temperature. Mammals may have larger internal organs than reptiles and thus a larger resting metabolism. The reptile–mammal difference in standard metabolism also exists when levels of maximal metabolism are considered.

  We mammals, with our relatively constant body temperature possess one of the finest examples of physiological homeostasis being favoured by evolutionary selection. This review will concern itself with the evolutionary sequence in which the many different mechanisms that allow mammals to maintain a constant body temperature have occurred. It is limited to mammals and will also not be concerned with the evolutionary history of the central control of body temperature. Basic thermo-regulatory control is much older than the mammals, since ectothermic vertebrates have both thermal detectors and a central nervous system activator (Hammel 1968).

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  Sturkie's Avian Physiology

  • G. Causey Whittow(Author)
  • 1999(Publication Date)
  • Academic Press

    (Publisher)

  Development of Thermoregulation

  A. Embryo

  B. Hatchling

  C. Nestling

  XIII. Summary

  References

  I INTRODUCTION

  Birds are among a minority of animals capable of effective regulatory thermogenesis. Such endothermic capacities are also evident either bodywide or, in some cases, within particular tissues in various insects; some large, fast swimming fish; a few large reptiles; and, of course, mammals. Like the last group, birds show in-pressive homeothermic capacities involving the balancing of rates of thermolysis and thermogenesis. These homeotherms are thus able to regulate body temperature within a narrow range over a wide span of thermal conditions.

  There is evidence that the high metabolic rates permitting endothermy did not exist in the earliest known bird Archeopteryx lithographica and may not have been completely established in the Class Aves until midlate Cretaceous times. The elevated metabolic levels characterizing modern members of this class may have originally evolved in response to selection for an increased capacity for long-distance flight, rather than as a requisite for flight itself. Endothermic temperature regulation would have been a by-product of this development (Ruben, 1996 ).

  Despite the fact that homeothermy probably arose independently in the avian and mammalian lines (Ruben, 1995 ), the general features of thermoregulation in the two groups appear quite similar. Nonetheless there are some behavioral and functional differences between them that influence the manner in which this regulation proceeds. Birds, with some important exceptions, appear in winter to make far less use than mammals of the thermal protection provided by underground or subnivian burrows, nests, and cavities in trees. Significantly, seasonal dormancy (hibernation) is rare in birds. However, many of these animals surpass mammals in evasion of adverse thermal conditions by long-distance migration (

  Dawson et al. , 1983a)

  . The relation between hypothalamic and spinal thermosensitivity differs between these groups (Simon, 1989 ). Furthermore, nonshivering thermogenesis appears absent or less prominent in birds than in the array of mammals possessing brown adipose tissue (Marsh and Dawson, 1989 ; Marsh, 1993 ). There are also differing considerations affecting insulation in the two groups. One relates to the fact that the avian plumage, unlike the mammalian pelage, generally must meet aerodynamic as well as insulative needs. Additionally, distribution of subcutaneous fat tends to be more localized in many birds than in mammals, which affects tissue insulation (Marsh and Dawson, 1989 ). Sweat glands have not been found in the former group and avian cutaneous water loss, which can be substantial (Marder and Gavrieli-Levin, 1987 ), must therefore proceed by a different mechanism than that employed by sweating mammals. Additionally, virtually all birds appear able to enhance respiratory evaporation by panting, whereas this ability is more restricted among mammals. Finally, the contrasting developmental patterns of the two groups (oviparity versus viviparity, excepting the prototherians) have important thermoregulatory implications. The development of the avian egg outside the body of the hen ties one or both parents to the nest and, except for mound builders and brood parasites, necessitates effective incubation patterns serving to maintain embryonic temperature within a narrow range suitable for development. These patterns can expose the incubating parent to extremely demanding thermal conditions (see, for example, Morton, 1978 ; Grant, 1982

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  Thermofluids

  From Nature to Engineering

  • David Ting(Author)
  • 2022(Publication Date)
  • Academic Press

    (Publisher)

  Ganslosser and Jann (2019) . When the environment is warmer than desirable, creatures including humans, apes, monkeys, horses, and hippos sweat. Dogs do not sweat much, instead, they reject heat effectively via evaporative cooling, that is, panting. To stay warm when the environment is colder than thermally comfortable, mammals can increase their body temperature by developing goosebumps, creating added insulation to reduce heat loss.

  Endotherms are warm-blooded creatures that maintain their body at a metabolically favorable temperature, regardless of the environment. This is achieved primarily by the use of heat released by their internal bodily functions.

  Ectotherms are cold-blooded creatures that rely heavily on external heat sources to regulate their body temperature. The heat produced by internal physiological sources is relatively small. That being the case, their body temperature varies with the environment.

  From the basic understanding of how animals interact with their natural environment, we can draw a parallel in engineering to facilitate our acquisition of thermofluids knowledge. Upon being fully fledged with natural ecological thermofluids, we can better engineer a nature-friendly tomorrow.

  An everyday example of an ectotherm is a frog, as shown in Fig. 5.1 . Frogs belong to the group of small vertebrates that survive in a moist environment. This group of animals is called amphibians, animals that can live both on land and in water, and they are cold blooded. Cold blooded implies that frogs adjust their body temperature to that of the environment that they are in. To put it another way, they do not warm themselves, like warm-blooded animals, by generating heat via metabolism. Since we are talking about frogs, let us take a few minutes to revel in the “Boiling Frog” fable, as illustrated in Fig. 5.2 . The fable is credited to Edward Wheeler Scripture (1897) , where he cited and utilized frog kinetics studies by Sedgwick (1883)

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  Theory and Applications of Heat Transfer in Humans, 2 Volume Set

  • Devashish Shrivastava, Devashish Shrivastava(Authors)
  • 2018(Publication Date)
  • Wiley

    (Publisher)

  et al. (2008). Reproduced with permission of Elsevier.

  Some animals (e.g., reptiles) are thermal conformers in that they allow their body temperature to vary with ambient conditions; these are ectothermal species. Mammals, on the other hand, are regulators that evolved with effector mechanisms designed to achieve a relatively stable mean body temperature (Brown and Brengelmann, 1970; Jessen, 1996; Werner et al., 2008), with that level generally being associated with good health and optimal function. Endothermy, however, comes at a physiological cost, and the narrower the zone of thermal indifference (thermoneutrality), the more costly are the homeostatic processes recruited to sustain that state. Consequently, homeostasis does not imply absolute thermal constancy, for there are circumstances in which it can be advantageous, and sometimes even protective, to regulate body temperature above or below the normothermic state. For instance, when exercising in the heat, the typical body temperature of a regulating, resting person (normothermia) drifts upwards. This permissive, yet regulated, mild hyperthermia simultaneously reduces dry-heat gain and elevates the cutaneous water vapour pressure, thereby increasing evaporative cooling without increasing sweat flow. In some circumstances, the mean body temperature rises and stabilises at a higher steady state. In more stressful conditions, a thermal steady state may not eventuate, but its elevation rate is autonomically reduced. These are tolerable and regulated states, although they both have finite tolerance limits. In the cold, the opposite occurs, with mild hypothermia reducing heat loss, with an eventual physiological amputation at the hands and feet in more extreme states serving to protect vital structures (Taylor et al

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  Psychoendocrinology

  • F. Robert Brush, Seymour Levine(Authors)
  • 2013(Publication Date)
  • Academic Press

    (Publisher)

  CHAPTER NINE

  Temperature Regulation

  Lawrence C.H. Wang and T.F. Lee

  Publisher Summary

  This chapter describes temperature regulation in organisms. The quest of achieving an optimal internal-thermal state to maximize biochemical efficiency encompasses both behavioral and autonomic efforts. Although superficially divergent in an internal-thermal state among the vertebrates, both ectotherms and endotherms share many common neural elements in sensing, deciphering, and responding to environmental thermal challenges. In the endotherms, autonomic capabilities allow the maintenance of a relatively constant internal-thermal state independent of environmental fluctuations. Neuroendocrine regulation of hibernation represents an important adaptive strategy for energy conservation under adverse conditions in many birds and mammals Changes in electrophysiological properties of an organism elicited by temperature are typically consequent of ionic or metabolic alterations, including changes in electrogenic sodium-pump activity and passive ionic permeability. This provides a neurophysiological basis for the warm sensation experienced by humans following intravenous calcium administration.

  I Introduction

  The optimization of an internal thermal state for maximizing biochemical efficiency is of obvious survival value to organisms. In ectotherms (poikilotherms), the selection of a preferred thermal environment is accomplished mainly by behavioral means, whereas in endotherms (homeotherms), the maintenance of a relatively constant internal thermal state requires both behavioral and autonomic measures. Although they appear superficially divergent, both ectotherms and endotherms share many common neural elements governing thermoregulation; for instance, temperature transducers for the detection of ambient and internal thermal states, integrators or comparators for deciphering whether or not the internal thermal state is optimal, controllers for the activation or the inhibition of specific behavioral or autonomic measures, and effectors to carry out specific thermoregulatory tasks. To appreciate fully the neuroendocrine modulation of thermoregulatory functions, especially among the endotherms, it is perhaps beneficial to first have a firm grasp on the functional aspects of the individual neural elements followed by an understanding of their regulation by the neuroendocrine influences. Due to space constraint, only the most relevant points will be included, but recent reviews on specific topics will be listed wherever appropriate. Thermoregulation under modified physiological states, e.g., sleep, fever, and hibernation, will also be included to reflect species adaptations. An emphasis has been placed on neuroendocrine regulation of hibernation, not only because it represents an important adaptive strategy for energy conservation under adverse conditions in many birds and mammals, but also because it epitomizes the biochemical and physiological versatilities evolution is capable of amplifying to an existing thermoregulatory function.

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  Physiology of Marine Mammals

  Adaptations to the Ocean

  • Michael Castellini, Jo-Ann Mellish, Michael Castellini, Jo-Ann Mellish(Authors)
  • 2023(Publication Date)
  • CRC Press

    (Publisher)

  Humans cannot survive for long in the ocean outside of equatorial regions because the water is much cooler than our core body temperature and carries heat away from body surfaces faster than our normal air environment. Marine mammals often have very thick layers of fur or blubber that can protect them from water as much as 40°C cooler than their body temperature, but this has mixed consequences. What happens if animals are in warm water, swimming hard, or lounging on land under the sun? Marine mammals must be able to keep cool in warm waters and stay warm in the cold ocean. How do they do both?

  THERMOREGULATORY SYSTEMS

  The answer is a range of highly evolved

  thermoregulatory

  systems that can both conserve and dissipate heat. Of course, a species’ ability to do either varies widely given their global distribution. Some cetaceans spend their entire lives in ice-laden waters while others migrate regularly between polar and tropical waters. Many temperate pinnipeds spend considerable time in cold water but haul out onto hot beaches, while polar pinnipeds haul out on sea ice or land in air temperatures that are dramatically lower than the water. A combination of physical, biochemical, and behavioral tools allows these animals to move effectively between temperature conditions that would be challenging for many terrestrial mammals.

  If we back up for a moment to put this into a larger perspective, both terrestrial and marine mammals are considered

  endothermic homeotherms

  . They generate their own heat and can maintain a constant body temperature well above that of the environment. It is one of the main characteristics that define them as a “mammal”. These groups were called “warm-blooded” in older literature, to distinguish them from the “cold-blooded” reptiles, amphibians, etc. In modern terminology, lizards, snakes, fish, and other groups are considered

  ectothermic heterotherms

  . This means that these animals are dependent on external sources to regulate their body temperature.

  Hypothermia

  (body temperature too cold) and

  hyperthermia

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  Heating with Wolves, Cooling with Cacti

  Thermo-bio-architectural Framework (ThBA)

  • Negin Imani, Brenda Vale(Authors)
  • 2021(Publication Date)
  • CRC Press

    (Publisher)

  Seigel et al. 1987 ).
• Hibernation: Hibernation is a multi-day torpor which heterothermic mammals use, presumably as a strategy to conserve energy. Heterothermic mammals can change between self-regulating their body temperature and allowing the external environment to influence it.

6.3. Controlling heat: active methods of thermal adaptation in animals

This section covers the active thermal adaptation strategies used by animals with the hierarchical categorisation of these shown in Figure 6-3 . As discussed in Chapter 5, a thermal adaptation strategy can be called active when it is associated with a change taking place in the body of an organism. These changes are involuntarily and linked to the physiology of animals. These changes occur in the cells, tissues and organs of the body.

Figure 6-3. The hierarchical categorisation of active thermal adaptation solutions.

6.3.1. Generating heat

Although ectotherms generally change their body in response to their environment, survival in extremes of cold or heat may not be possible. This has been suggested as the reason for some ectotherms having mechanisms for adjusting their body temperature irrespective of the thermal condition of their environment (Davenport 2012). Examples include tuna fish, which have a counter-current blood circulatory system which results in an increase in the temperature of their bodily muscles (Legendre and Davesne 2020