ANIMAL PHYSIOLOGY HANDOUT
PHYSIOLO PHYSIOLOGY GY DEFINED DEFINED:: establ establish ishmen mentt of space space-ti -time me relati relations onship hips s betwee between n physical and chemical events within the organism as a response to events both within the organism and in the environment. MAJOR SUB-DIVISIONS of animal physiology 1. CELL PHYSIOLOGY: it deals with the events that occur within cells and the function of a cell per se. It also is concerned with the coordinated activities of cells. It tends to be strongly based in biochemistry. biochemistry. 2. ORGAN or WHOLE ORGANISM PHYSIOLOGY: which deals primarily with the way large groups of different cells (organs) interact with other organs or with how the entire organism behaves a physiological physiological unit. Specific Approaches Approaches to Animal Physiology: 1. Comparative Physiology: studies the underlying underlying physiological physiological similarities and differences of organisms. 2. Physiological Physiological Ecology: primarily concerned with understanding and describing the the phys physio iolo logi gica call mech mechan anis isms ms that that allo allow w an orga organi nism sm to live live in a part partic icul ular ar environment. 3. Mammalian (human) Physiology: emphasis is on medically-related medically-related problems, this is the best funded and most workers are in this area. As a result, many of the basic discoveries in physiology occur in this field. CONTROL SYSTEMS In order to understand regulation, we need to understand control systems. A control system consists of a series of components that work together to control some process. It is important important to realize that several components may in some cases reside in a single cell while in other cases many different cells or even tissues may make up one part of a control system. 1. CONTROLLED VARIABLE: the factor that we wish to regulate. Some type of SENSOR monitors the value of the controlled variable and sends this information to an error detector. 2. SET POINT: the desired value of the controlled variable. As an example, for alert but not active humans the set point for body temperature is 37º C. The value of the set point is often relayed to a place called the error detector as a REFERENCE SIGNAL. SIGNAL. 3. ERROR DETECTOR: a device that compares the value of the controlled variable with the set point. It produces a signal (ERROR SIGNAL) that then operates one or SYSTEMS. more EFFECTOR SYSTEMS.
ENERGETICS: ENERGETICS : the study of how energy transformations take place and how these affect the organism. THERMODYNAMICS : THERMODYNAMICS: law: matter/e 1. First law: matter/energy nergy is neither neither created created nor destroyed destroyed in any process, process, it simply changes form. (The law of conservation of matter/energy). Thus, we know that: a. For mass: the total amount of material that enters an organism must equal that which leaves or which remains a part of the organism. b. Likewise, for energy: the total energy obtained by food or via some physical means (e.g. sunlight, heat) must either remain stored in the organism or be lost to the environment. environment. 2. Second Law: in any SPONTANEOUS PROCESS the entropy of the UNIVERSE must increase. By entropy, of course, we mean disorder. METABOLISM is usually viewed as the sum of two processes: CATABOLISM and ANABOLISM (+ movement). a. Catabolism -- reactions that break down complex compounds often with the purpose of energy release with the goal of temporarily conserving some of the released energy in compounds such as ATP. Movement: reactions that use energy to join relatively simple b. Anabolism and Movement: compounds into more complex ones (ex: protein synthesis, DNA synthesis, etc) or which produce motion. •
Catabolic processes are thermodynamically favorable, anabolic and movement processes are not.
METABOLISM AND ITS MEASUREMENT MEASUREMENT:: Meta Metabo boli lism sm is indi indica cati tive ve of the the magn magnit itud ude e of at leas leastt thre three e very very im impo port rtan antt physiological factors: 1. GROWTH AND REPRODUCTIVE RATE (i.e., rates of synthesis) ACTIVITY -- energy needed to operate the various biochemical pathways needed 2. ACTIVITY -directly and indirectly in mechanical locomotion. 3. COMPLEXITY , since presumably the more complex the organism, the greater the metabolism required to maintain that complexity. complexity. HOW DO WE MEASURE METABOLISM? Energy: Metabolic Cost: Cost: Nearly all all chemical reactions involve involve changes changes in stored stored PE) such as the release or absorption of heat or some energy (potential (potential energy, PE) other type of energy. The total heat released by an organism can be used as an estimate of an organism's metabolism; measure metabolic cost as heat production, with units either of calories or Joules.
Power: Metabolic Rate: Rate: the metabolic rate has units of power -- usually usually watts watts or calories per time. METHODS USED TO DETERMINE METABOLIC RATE or METABOLISM METABOLISM:: a. The "WHAT COMES IN MUST GO OUT" method - sum all of the PE contained in materials that go in and out of an organism: b. HEAT PRODUCTION -- Direct Calorimetry Encase the organism in a calorimeter and measure the heat production. The heat heat produc productio tion n is propor proportio tional nal to the total total metab metaboli olic c rate rate since since the doing doing of chemical work results in heat production as a by-product. THE THE MEASU EASURE REM MENT ENT OF MET ETAB ABOL OLIS ISM M AND AND MET ETAB ABOL OLIC IC RATE RATE USIN SING OXYGEN CONSUMPTION AND CARBON DIOXIDE PRODUCTION Metabo Metabolis lism m can be measur measured ed in aerobic organ organism isms s by recor recordin ding g O2 consumption consumption and CO2 production. This requires that the organism must, as a whole be acting aerobically when the measurements are taken. Thus, if any anaerobic metabolism is occurring in some tissues, its effects must be reversed elsewhere in the organism. For most animals, this will mean that if any anaerobic by product is being produced (for example, lactic acid) it must be used up (not eliminated) by some other part of the body. If anaerobic products build up (increase) or if they are eliminated from the body, then the entire energy demand cannot be estimated just from anaerobic processes. The The ATP ATP cycl cycle. e. Anabol Anabolic ic react reaction ions s and moveme movement nt (m (musc uscle le action action,, activ active e transport, exocytosis, etc.) are non-spontaneous processes. Thus, they all require some sort of energy source and that source is usually ATP. These processes that need energy from ATP is referred to as "DEMAND " DEMAND"" reactions. The reactions that take energy from complex, energy storage molecules such as carbohydrates or fats and transfer some of that energy to the formation of ATP (or more simply ~P) is referred to as the "SUPPLY" " SUPPLY" reactions. The rate of the demand reactions is set by some factor (for instance the need to grow or move) and the supply must meet it. ATP is used to shuttle energy from the energy-rich compounds degraded in the supply reactions to those needing energy in the demand side. The supply reactions must be adjusted to keep the level of ATP roughly constant. Aerobic Metabolism and the RQ Concept Concept* * In most animals, most of the supply reactions responsible for the generation of ~P occur occur in the mitochon mitochondria dria (e.g., Krebs Krebs cycle, cycle, oxidativ oxidative e phosphor phosphorylat ylation, ion, β− oxidation of fatty acids). They are closely related to other reactions that occur in the cytosol (glycolysis and some types of protein and lipid metabolism).
mitochondria. 1. In aerobic organisms most ~P comes from the mitochondria. KREBS CYCLE (TCA): (TCA): degrades 2C (acetyl) compounds into lots of high-energy electrons and some ~P. Nearly all of the energy is removed from the fuel molecules in the form or highenergy electrons. The carriers that actually move the electrons are the coenzymes NAD+ or NADoxdized and FAD. FAD . When these are reduced by the addition of NADH (NADredu (NADreduced) ced) and FADH2 FADH2 respectiv electron electrons, s, they become become NADH respectively. ely. The energy in these electrons is ultimately extracted by the electron transport system (ETS) and is used to produce ~P by a process called oxidative phosphorylation. Some ~P is also produced by a process called substrate-level phosphorylation. phosphorylation. Substrate-level phosphorylation can be defined as the process where a ~ P is created on a substrate molecule and is then transferred to some other molecule -- for instance ADP or GDP to make ATP or GDP. In the case of the Krebs cycle, the substrate-level phosphorylation involves the production of GTP. A single ~P is produced by substrate level phosphorylation per 2C that enters the Krebs Cycle. The rate of the Krebs Cycle is controlled by: 1. availability of appropriate 2C compounds 2. availability of electron of electron acceptors (NAD+ and FAD). 3. the concentrations of certain enzyme modulators such as ADP and ATP. sources : The Krebs cycle gets its fuels from one of three sources: Carbohydrate, 2C fragments after processing in glycolysis (cytosol) and the 1. Carbohydrate, mitochondrial "bridge reaction (PDH complex rx)". 2. Fatty Fatty acids via β-oxidation in the mitochondria -- this feeds 2 C fragments in to the cycle at the same place as carbs enter. 3. Sometimes (rarely in humans) by oxidation of the skeletons of amino acids -these are basically what are left of an amino acid after it has been deaminated (after the -NH2 is removed). * CO2 is the Krebs cycle waste product . The CYTOCHROME ELECTRON TRANSPORT SYSTEM (ETS) : (i) The ETS accepts high-energy electrons electrons produced by the Krebs cycle and by other mitochondrial and cytosol reactions such as glycolysis and β-oxidation. (ii) These electrons are eventually transferred in an orderly manner from one carrier to the next until they eventually combine combine with oxygen and form water. (iii) In the process, energy from the electrons is used to form ATP from ADP and Pi by a process involving pumping and re-entry of H+. (iv) The amount of energy that can be conserved in ~P depends on the source of the electrons. Electrons from NADH are more energetic than those from FADH2 .
The ETS is able to conserve 3 ~P per electron pair from NADH (one pair NADH) and 2 ~P per FADH2 (one pair of electrons per FADH2). The ETS is controlled by: 1. Availability of O2 of O2.. FADH2. 2. Availability of NADH of NADH or FADH2. 3. Ratio of ATP to ADP –ADP must be present to allow the system to work. Keeping track of conserved energy energy:: Per 2C that entered the Krebs cycle, we got: (a) 1 ~P directly by substrate level phosphorylation (b) 3 NADH, each of which will give up their electrons to the ETS and produce 3 ~P -- so the total amount of ~P made from the NADH yielded in one turn of the Krebs cycle is 3* 3 = 9. (c) there was 1 FADH2 which will give a pair of electrons to the ETS and yield 2 ~P. ~P . (d) Total Total is 12 ~P. GLYCOLYSIS: GLYCOLYSIS: a system that is resident in the cytosol. It takes glucose (and other substances) substances) and converts to them into 3C fragments. Energy-wise, ATP is generated from ADP and Pi via substrate-level phosphorylations and high-energy electrons are produced and captured by NAD+. However, these can only be used to synthesize ~P under aerobic conditions. The input is always a hexose sugar or hexose derivative. It can either be glucose (or a number of other hexoses) or glycogen. glycogen . If we start from glucose, two ~P are expended in preparing the molecule for the degradative parts of glycolysis. If we start from glycogen, only one is needed because a hexose is cleaved from glycogen using a Pi. hexose, we get two molecules of "waste" "waste" at the bottom. Under aerobic (a) per hexose, condition conditions, s, this waste is pyruvate (the conjugate conjugate base base of pyruvic pyruvic acid). Under aerobi aerobic c condi conditio tions, ns, the pyruv pyruvate ate will will go the the mitoch mitochond ondria ria and be comple completel tely y oxidized in the "bridge reaction" and the Krebs cycle. hexose, there are a total of 4 substrate level phosphorylations (i.e., (b) per hexose, two per pyruvate). hexose, there are two molecules of NADH produced from NAD+. Under (c) per hexose, aerobic conditions, the electrons on these NADH will eventually end up in the ETS. So, here is the summary: Energy Gains: Gains: 1. From substrate-level phosphorylations phosphorylations -- a total of 4 of 4. 2. 2 NADH (two pairs of high energy electrons) – the number varies between 2 and 3 depending on the cell type. In muscles it is usually 2 and in the liver it can be 3.
* We only only get get 2 ~P from from ox oxid idat ativ ive e phos phosph phor oryla ylati tion on for each each NADH NADH prod produc uced ed in glyc glycol olys ysis is.. That That give gives s a to tota tall of 4 ~P from from ox oxid idat ativ ive e phosphorylation. 3. Gross ~P yield = 4 (substrate level) + 4 (ox-phos) = 8 ~P total . Energy costs: costs: if our hexose was glucose, we paid 2 ~P and if it was glycogen our imme im medi diat ate e cost cost was was 1~P 1~P (we (we paid paid the the othe otherr one one earl earlie ierr in synt synthe hesi sizi zing ng the the glycogen). Thus, costs are 1 or 2 ~P. Net Yield: Yield: Gross - "cost": for glucose, 8 - 2 = 6 ~P , from glycogen, 8 -1 = 7 ~P. ~P. Wastes: Wastes: two 3-carbon molecules (pyruvate). (pyruvate). Gett Gettin ing g from from Glyc Glycol olys ysis is to the the Kreb Krebs s Cycl Cycle e -- the the so so-c -cal alle led d "bri "bridg dge e reaction" (PYRUVATE DEHYDROGENASE COMPLEX REACTION OR THE PDH RX FOR SHORT) If the Krebs cycle is going, and there is adequate NAD+ and FAD, it will be able to accept more 2 C fragments. Pyruvate, the "waste" product of aerobic glycolysis has 3 C. To use it in the Krebs cycle, we must remove one carbon. This is done by the "bridge reaction" -- more properly, the pyruvate dehydrogenase reaction; this occurs in the mitochondrion. mitochondrion. Energetics of the "bridge reaction": the NADH molecules produced by the pyruvate kinase reaction will yield 3 ~P each since they are produced within the mitochondria. Since the pyruvate dehydrogenase (a.k.a. bridge) reaction will occur twice per hexose that enters glycolysis (since we get two pyruvates), then a total of 2 NADH are yielded which gives us a total of 6 ~P. How much ~P is yielded per hexose? 1. From glycolysis: 6 or 7 2. From the "bridge": 6 3. From the Krebs cycle and ETS: 24 4. TOTAL: 36 or 37 per hexose 5. waste products -- 6 CO2 and 6 H2O ANAEROBIC METABOLISM ANAEROBI ANAEROBIC C METABOL METABOLISM ISM:: where something different than oxygen. oxygen.
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Glycolysis can be either aerobic or anaerobic, in the sense that if there is adequate O2, electrons produced in glycolysis enter the mitochondria and the ETA and and even eventu tual ally ly are are atta attach ched ed to O2 and and H+ to form form wate water. r. Thus Thus,, in aero aerobi bic c metabolism, metabolism, O2 is the ultimate electron acceptor. RELATIVE OR ABSOLUTE LACK OF O2 O2::
Relative: Relative: More electron electrons s are being produced produced by the Krebs Krebs cycle and glycolys glycolysis is than can be accepted by the ETS. There may be large amounts of O2 present, they are are sim simply ply not large large enough enough to accept accept all the electr electrons ons being produce produced. d. If no alternative acceptor can be found for these electrons, the cell will run out of the oxidized form of NAD and this will decrease or stop glycolysis and the Krebs cycle. ~P production will be reduced or stopped. Absolute: Absolute : Here, there there is no O2 present present (anoxia) (anoxia) and therefore therefore the ETS cannot cannot accept electrons. Since the Krebs cycle is highly dependent on the ETS, it will stop, but it is still possible for glycolysis to proceed if there are alternative means of storing these electrons until later. The crucial step in making glycolysis anaerobic is to find an alternative acceptor for the NADH produced in glycolysis. There are many ways this is done. Here are the two most famous: (a) the production production of lactic acid (lactate): (lactate): Lactate is simply simply reduced pyruvate. pyruvate. One reason for the common use of this particular pathway is that pyruvate produc productio tion n is the termin terminal al step step in glycol glycolysi ysis, s, there therefor fore e using using it as an alternati alternative ve electron electron acceptor acceptor in anaerobic anaerobic glycolysis glycolysis allows allows the entire entire process to be self-contained. (b) the production of of ethanol: In the normal activities activities of an animal, there are are many situations where anaerobic metabolism is significant. The most common situations are are heav heavy y exer exerci cise se or any any prol prolon onge ged d exer exerci cise se in anim animal als s that that are are prim primar aril ily y "designed" for burst type activities. The role of anaerobic glycolysis in the former group is to provide higher ~P production (metabolism) (metabolism) rates than can be sustained aerobically. This need typically occurs under high workload conditions such as sprinting. Examples of latter would be many reptiles, amphibians, fish and spiders -animals that primarily capture prey by ambush or quick motion. These animals are also called "sit and wait" predators. If they are forced to exercise for long periods of time, they rely on anaerobic metabolism as they simply lack well developed aerobic pathways. What happens to the lactic acid? 1. The side effects of high [lactic acid ]: the principal principal side effect of lactic lactic acid is that it lowers cellular pH. This affects the conformation of all proteins within the cell. Generally the cells can tolerate a degree of pH shift, but large amounts of lactic acid accumulate accumulate the pH change will be large enough to significantly affect the structures fatigue. of a broad range of proteins. The result is the reduced function that we call fatigue. There are also psychological effects of high [lactic acid] -- we generally experience such concentrations as a burning sensation in active muscles. 2. Removal of lactic acid: lactic acid is not a waste in animals. That is because it contains abundant energy (remember it is reduced pyruvic acid and pyruvic acid is
normally oxidized in the Krebs cycle for energy). However, the cells that make lactic acid typically need to get rid of it because when they make it they are doing so because, they lack sufficient O2 to oxidize it and also because of the pH problems just mentioned. And And so, like in bacteria, bacteria, the cells simply dump dump the lactate -- in this case case into into the blood blood where it quick quickly ly is dilute diluted d and therefo therefore re causes causes less of a problem. As to what happens next, that depends: (a) The The heart can oxidize lactate to CO2 and water . Lactate is a preferred fuel of the heart muscle. The heart usually has no trouble dealing with lactic acid since it has abundant O2. It handles it by reversing the LDH reaction to get NADH and pyruvate. The NADH is oxidized by the ETS to give ATP and the pyruvate proceeds through the Krebs cycle as usual. In this case, glycolysis starts in some muscle tissue and produces lactic acid which is then oxidized in the heart. The net result is aerobic glycolysis where the first steps occur in the muscle (the anaerobic steps) and aerobic completion occurs in the heart. The heart may get 50% of more of its energy from lactic acid during exercise. (b) GLUCONEOGENESIS. In this case, the lactic acid is picked up by the liver (or sometimes other tissues). It is converted back to glucose at a net cost of energy. Gluconeogenesis is an aerobic process. It generally proceeds at a slow rate. When associated with exercise, gluconeogenesis occurs mostly during the recovery period after the exercise. Gluconeogenesis is an umbrella term for a number of processes that produce glucose from other compounds. Starting points can also be a number of amino acids, Krebs cycle intermediates, or fatty acids. Since the accumulation of anaerobic products is associated with fatigue, activity with an appreciable anaerobic component can only be sustained for a limited duration of time. Activities NONSTEADY STATE with appreciable anaerobic components are referred to as NONSTEADY ACTIVITIES. ACTIVITIES. Here it refers to whether or not the exercise can continue.
The Regulation of Cellular Metabolism Metabolism* * Some Important Important Factors Factors Which Which Determi Determine ne Reaction Reaction Rates Rates in Biologica Biologicall Systems Flux is the rate at which material passes through a pathway or any of its steps (the term is also used to discuss the turnover of energy or movement of substances). B. Enzyme activity: activity: "A"ase A -----------------> B Enzyme activity is a term that refers to the amount of functional enzyme present (here the enzyme "A"ase) in some tissue or solution. It is measured in terms of the amount of product produced per unit time (flux) under ideal conditions and is
usually normalized to the amount of protein present (not all the protein will be the enzyme of interest) or to the amount of tissue the enzyme was removed from. The most important single factor is the amount of functional enzyme present activity). Most reactions in organisms are increased by (also known as the enzyme activity). a factor on the order of 107 over the same reaction outside of the body. When compared under the same conditions of temperature, pressure, pH, and the same chemi chemical cal envir environm onment ent,, the magnit magnitude ude of the increa increase se depend depends s sim simply ply on the availability of functional functional catalyst -- the more enzyme, e nzyme, the faster the reaction rate. determined by gene expression expression The functional amount that is present is determined and by various factors that modulate the functionality of the enzyme molecules chemicall and that that are are prese present. nt. These These inclu include de both both specific modulators and chemica physi physical cal facto factors rs such as pH, pH, ion ionic concen ncentr tra atio tion, and temp emperat eratur ure. e. Temperature, Temperature, independent of its effect on enzyme structure has its usual role in accelerating reactions. Enzyme Catalyzed Reactions in Pathways Pathways.. 1. Equilibrial reactions are the most common type -- here the functional enzyme is in sufficient quantity that it converts reactant into product very fast. The result is always close to equilibrium equilibrium regardless regardless of the the flux. Flux that the reaction is always through any equilibrial reaction is largely determined by the availability of reactants and the removal of products, not by regulating the functionality of the enzyme. 2. Non-equilibrial reactions are rarer but are extremely important in regulating the flux through pathways. They are called non-equilibrial non-equilibrial because at least some of the time the mass action ratio is very far from equilibrium. equilibrium . The enzyme catalyzing this step is regulated into a shape that makes it a poor catalyst. As a result, reactants accumulate due to the action of reactions upstream from the non-equilibrial step and meanwhile reactions that are downstream drain off much of the product. TEMPERATURE REGULATION: ECTOTHERMY * What are the effects of temperature on an animal (or plant)? There are several answers to this question, some have to do with direct effects on rates of reaction, others with avoidance of physical damage to membranes and proteins, others with points that make optimal use of energy available for certain processes. Three terms relating to the temperature range an organism tolerates should be learned: Stenothermic: tolera narrow range range of temper 1. Stenothermic: tolerates tes only a narrow temperatu atures res:: ex. many many tropical and deep-sea organisms. organisms. Eurythermal: tolerates a wide range of temperatures. 2. Eurythermal: temperatures.
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The two terms above may be applied to both daily swings in temperature and also to seasonal changes.
temperature: the preferred temperature. 3. Eccritic temperature: LETHAL LIMITS: LIMITS: these are temperatures that are incompatible with life. Lethal limits are established by determining LD50s. Lethal dose 50%: points of exposure where 50% of a population dies. Obviously this implies both the temperature and duration of exposure to that temperature. Why do different temperatures kill organisms? -- The effects of extreme temperatures 1. Cold -- the effects of freezing a. physical damage to structures caused by the formation of ice: the membrane bound structures are destroyed or damaged. b. chemical damage due due to the the effect effects s of high high solut solute e concen concentra tratio tions. ns. When When freezing freezing occurs, occurs, solute solute concentra concentrations tions increase increase in non-froz non-frozen en areas. areas. These These high concentrations concentrations may denature enzymes, etc. Heat: 2. Heat: a. inadequate O2 supply for metabolic demands (especially in areas where O2 is low, such as water and burrows) b. rapid depletion of substrate substrate stores 3. Heat and Cold a. reduced activity or denaturation of proteins -- the inactivation of certain proteins with the result that metabolic pathways are distorted. b. disruption of enzyme pathways by differential temp effects on different enzymes (like b, except what happens here is that temperature affects different reactions in different pathways differently. fluidity :. These lead to problems with any membrane c. effects on membrane fluidity:. dependen dependentt function function;; the nervous nervous system system is especial especially ly prone prone to disrupti disruption on from fluidity changes. The types of fatty acids in a membrane determine the motility of substances in the membrane and therefore their ability to interact with each other and allow substances that require protein mediated transport to pass through the membrane. a. This effect is due to the inter-relationship between temperature (which causes a certain mean velocity for membrane molecules) and the structure of the fatty acids making up the lipid bi-layer. b. At a given temperature, the more saturated fatty acids that are present, the less fluid the membrane will be. This is because saturated fatty acids are relatively straight chains and can easily be packed into a membrane, producing a stable and not very fluid result.
By contrast, unsaturated fatty acids have bends at the location of every double bond; as a result, they cannot pack as effectively into a membrane and the membrane tends to be more fluid. GENE GENERA RAL L EF EFFE FECT CTS S PROCESSES
OF TE TEMP MPER ERAT ATUR URE E
ON CHEM CHEMIC ICAL AL
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PHYS PHYSIC ICAL AL
PROCESSES: all chemical reactions leading 1. CHEMICAL REACTION MEDIATED PROCESSES: to such macro phenomena as: muscle contractions, nerve transmission (both of these relate to sensation and movement), digestion, growth, etc. UNCATALYZED UNCATALYZED REACTIONS. REACTIONS. Many Many chemical chemical reactio reactions ns commonl commonly y double double their rate with a 10oC increase in temperature. PROCESSES: these 2. PHYSICAL PROCESSES these often often depend dependent ent on temper temperatu ature re to a lesser lesser degree than chemical processes. POIKILOTHERMY -- TEMPERATURE CONFORMITY Many animals are totally totally incapabl incapable e of temperatu temperature re regulatio regulation. n. Their only significant source of heat is the environment and their body temperature is directly determined by the ambient temperature. The temperature conforming animals are poikilotherms. METABOLISM TENDS TO INCREASE WITH BODY referred to as poikilotherms. TEMPERATURE. Poikilothermy is the condition of many organisms and all isolated tissues or cells. Many animals can regulate their overall body temperature, their individual organ organs s and tissu tissues es do not have have this this proper property ty and act act poikil poikiloth otherm ermica ically lly.. Heart Heart surge surgeons ons take take advant advantage age of this this by perfus perfusing ing the the heart heart (and (and someti sometimes mes other other tissue tissues s also) also) with with cool cool blood. blood. This This lowers lowers the metabo metabolis lism m of the organ organ(s) (s).. Any organism can be turned into a conformer -- when its ability to regulate is exceeded. ECTOTHERMY : a term preferred to poikilotherm. SUBHEADINGS SUBHEADINGS of ectothermy, divided as to the identity of the major source of heat. HELIOTHERM: the sun is the direct source of heat. So, these are ectotherms that a. HELIOTHERM: use the sun as their most significant significant direct heat source. THIGMIOTHERM: warm substratum or medium (and not the sun directly) is the b. THIGMIOTHERM: main heat source. HOMEOTHERMY : this simply refers to a constant body temperature, presumably maintained by some sort of regulatory mechanism. However, many also apply this term to animals that live in very constant thermal environments environments that therefore have very little in the way of changes in body temperature. ENDOTHERMY : the primary source of heat is internal chemical reactions. HETEROTHERMY : An animal that acts like an endothermic homeotherm part of the time and like a poikilothermic poikilothermic ectotherm the rest of the time.
The costs involved in temperature regulation fall primarily under two categories: TIME and ENERGY ectotherms , to regulate temperature they must a. Time is most important for ectotherms, go in and out of the sun or hide when cold. b. Energy is the big cost for endotherms since the costs associated with a high rate of metabolism are so large. It also involves a large time cost for many species due to the time they must spend looking for and eating large amounts of food. Both of these factors may result in great limitations on how small an animal can be and still be an endotherm. They also relate to the particular ecological ecological niche that is possible for an animal. TEMPERATURE REGULATION: ENDOTHERMY * I. Endothermic Temperature Regulation Anima Animals ls that that more more or less less const constant antly ly regula regulate te their their body body temper temperatu atures res EUTHERMIC. endothermically endothermically are often referred to as being EUTHERMIC. 1. Eutherms include most all mammals and birds during most of their lives (and for many species, all of their lives). 2. By contrast, another group of endotherms includes animals that only regulate their their temper temperatu ature re endoth endotherm ermica ically lly for a sm small all portio portion n of the time. time. These These are are INTERMITTEN TENT T ENDOTH ENDOTHERMS ERMS.. Many refe referr rred ed to as HETEROTHERMS or INTERMIT mammals and birds fall into these groups for at least part of their lives. In addition, ther there e are are many many spec specie ies s of inse insect cts s and and some some fish fish and and rept reptil iles es that that also also are are intermittent endotherms. However, even in eutherms not all parts of the body are regulated at the same temperature. temperature. Some definitions: core: the a. The The core: the port portio ions ns of the the body body,, usua usuall lly y deep deep in the the anim animal al and and most most containing important organs whose function is most dependent on a constant high body temperature. In most vertebrates the core includes the brain and perhaps the heart and digestive system or the entire viscera. b. The remainder of the animal is termed the periphery and is regulated to various degrees. For instance, the temperature of the skin and to a lesser degree much of the limbs is less regulated than the core. These areas may get relatively warm or even even approa approach ch freez freezing ing with with longlong-ter term m harm harm or withou withoutt totall totally y knock knocking ing out function. ACCLIMATIZATION: the ACCLIMATIZATION: the long long-t -ter erm m (chr (chron onic ic)) adju adjust stme ment nts s that that are are made made to seasonal changes in temperature. ACCLIMATION: ACCLIMATION: short-term changes quickly made to a changing set of conditions. This term is very often applied to adjustments that are made by an animal to some
specific set of laboratory conditions. Thus, it is fair to say that they differ from acclimatization acclimatization in being acute rather than chronic changes. COMPENSATION: COMPENSATION : A proce process ss whose whose end result result is to maint maintain ain a consta constant nt state state regardless of the conditions, i.e. a constant average daily metabolic rate regardless of the season through thermal acclimatization. acclimatization. Endothermy in Fish, Snakes, Turtles, And Lizards. A. Fish 1. The difficulties that a potentially endothermic fish must face when compared to an endothermic terrestrial animal: a. The heat capacity of water is much higher than that of air and slightly higher than tissue (which is mostly water). Thus, compared to a terrestrial animal, an aquatic animal experiences rapid loss of any heat the animal generates. b. O2 concentrations of water are much lower than in the air -- therefore to get a given amount of O2, a fish must breathe a greater volume of water than must an air breather must breathe air: In many fish there are two distinct groups of muscles: the largest mass is made up of white muscle and is used for sprinting and the smaller mass is red muscle. The red muscle is located surrounding surrounding the spine and the coelomic cavity (containing the gut and other organs). It is used for "cruising"; in other words, it is continuously active as the fish makes its way around. The red muscle is the heat source: a. it is continuously active b. it is at the core whereas white muscle is nearer to the periphery c. it surrounds the organs -- warming them will increase rates of digestion etc. Other unusual examples of endothermy in vertebrates. vertebrates. What body shape found in a terrestrial vertebrate would seem least conducive to endothermy? Ans.: snake, due to large area of contact with the ground (much more thermally conductive than the air). Python, At least one snake is an endotherm during part of its life: the Burmese Python, a comm common on python python sold sold in many many pet stores stores,, it grows grows up to about 20 feet. feet. The females wrap around their eggs and contract their muscles to generate heat and incubate the eggs. During this time, the females maintain an appreciably elevated body temperature. Endothermy in Insects: Flight is the most energetically demanding activity that any animal performs; there there are many situation situations s where where a high body temperature temperature will aid in achievin achieving g flight.
1. This is most true in insects that have relatively great mass and small wings: i.e., high wing loading. loading. Examples Examples are the highly maneuverab maneuverable le insect insect such as bees, bees, dragonflies, some large flies, moths, and beetles, and certain other insects such as some cicadas, crickets and grasshoppers. 2. Large insects with lightly loaded wings (e.g. butterflies, many moths) do not flap their wings often enough to generate enough heat to be endothermic. 3. Many other insects are Behavioral Thermoregulators: this is especially true of butterflies.
