B6A8Thermoreg - Homeostasis & Thermoregulation The...

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Unformatted text preview: Homeostasis & Thermoregulation The The Body’s Body’s Internal Environment Internal Environment A Dynamic Constancy Integration & regulation: “the whole is greater than the sum of its parts” Why is Homeostasis so important? Homeostasis: maintaining a Optimal temperature for typical human enzyme Among other things … • Proteins Rate of reaction constant, optimal internal environment – including the enzymes and other molecular machines that run everything, • are very sensitive to deviations in conditions 0 20 Optimal temperature for enzyme of thermophilic (heat-tolerant) bacteria 40 Temperature (C º ) 80 100 (a) Optimal temperature for two enzymes – Esp., temp & pH – D protein shape fi ∅ fx Conformers & Regulators • Conformers: allow internal environment to conform to external • Regulators: use control mechanisms to maintain constant internal environment despite external variations • Note: an organism may be different for different variables – The same fish may be a thermoconformer and an osmoregulator Heyer Conformers vs. Homeostasis? • How can they be homeostatic and conforming? • Live in a stable environment – At least with respect to the conformed variable and/or • Be able to make new versions of proteins for each variation otter & bass from same stream – Requires larger genome – Transition to new condition must be gradual enough to allow sufficient expression of new proteins otter & bass from same stream 1 Homeostasis & Thermoregulation For Example: Environmental Heat Transfer Thermoregulation • • • • • Poikilotherm (variable temp ): body temp (T B) varies with environment temp Radiation: radiant energy absorbed/rereleased as thermal rereleased as Radiation: radiant Conduction: direct ttransfer of thermal energy Conduction: direct ransfer of thermal energy Convection: thermal energy absorbed by medium Convection: thermal Heat of evaporation: evaporating water absorbs energy evaporating Heat • Homeotherm (same temp ): maintains constant TB • Ectothermic: most of body ’s thermal energy acquired from environment • Endothermic: most of body ’s thermal energy derived from otter & bass from same stream metabolism Poikilotherms not necessarily “cold blooded ” Metabolic Heat Production Metabolic Heat Production • Energy cannot be created nor destroyed • Energy can be transformed • All energy transformations lose some energy as heat Food energy + O 2 Cell respiration ADP CO2 + H2O + energy ATP Cell work Standard metabolic rate (SMR )— in poikilotherms: • Minimum metabolism to produce sufficient ATP for running ion pumps (electrolyte gradients), heart & ventilation muscle activity, etc. (sleeping/fasting) at standard temp Basal metabolic rate (BMR )— in homeotherms: • SMR + energy demand to keep body warm Metabolic Heat Production Metabolic Heat Production Food energy + O 2 Cell respiration Food energy + O 2 Cell respiration ADP Cell work CO2 + H2O + energy ATP HEAT ↑cellular work ( esp . muscle activity) Æ ↑demand for ATP Æ ↑ metabolic rate Æ Heat production Heyer HEAT ADP Cell work CO2 + H2O + energy ATP HEAT Estimating metabolic rate: • Measure rate of – Net food energy consumption – Oxygen consumption – Carbon dioxide production – Heat production 2 Homeostasis & Thermoregulation Once again, … Environment also matters! Size Matters! • Heat exchange with the environment is proportional to body surface area (x 2) • Heat generation from metabolism is proportional with body mass (or volume = x 3) • Conduction & Convection in Aquatic vs . Terrestrial — • Water absorbs heat energy 50 –100x faster than does air! ↑x fi↑x 3 increases faster than ↑x2 – Small organisms have a large sa/v ratio 10 • Ectothermy favored – Large organisms have a small sa/v ratio • Endothermy favored 600 1000 0.6 • It ’s near impossible for a small aquatic organism to be endothermic • It ’s near impossible for a large terrestrial organism to be ectothermic Size & Environment Matter! Poikilotherms — Poikilotherms Conduction & Convection in Aquatic vs . Terrestrial — toleration ≠ thriving Even if can survive D temps, do best in a small range • Water absorbs heat energy 50 –100x faster than does air! • ↑↑ TBÆ↑ stress & mortality Marine iguanas of the Galapagos • Juveniles & adult females feed on exposed intertidal alga • Only large males have sufficient body mass to generate enough heat to forage underwater • ØØ TBÆØ metabolic rate & activity • Lizards — – Ø discrimination in T-maze tests – D b ehavior: warm lizards flee; cool lizards threaten Western fence lizard Poikilotherms — Poikilotherms Tolerating extreme cold Poikilotherms — Poikilotherms Tolerating extreme cold How can your proteins work below freezing? How can your proteins work below freezing? • Make unsaturated fats in membranes to remain fluid • Give up! — Go dormant • Concentrate antifreeze alcohols ( esp. glycerol) in tissues to lower freezing point • • Synthesize ice-binding proteins to prevent ice crystals from growing Largest land animals in Antarctica are tiny mites & springtails — freeze quickly most of year; thaw quickly to scavenge seal castings in brief warm season • Frogs and others: – ice on skin Æ adrenalin rush Æ liver glycogen released as glucose Æ cells concentrate glucose to lower freezing point – 67% of body freezes solid, but cells remain fluid down to –5°C. – Regains activity within hours of thawing Ice fish under the polar ice cap Heyer A frozen arctic wood toad 3 Homeostasis & Thermoregulation Homeotherms • Behavioral homeothermy • Physiological homeothermy Behavioral Homeothermy • Live in a stable environment or • Move with the constant conditions • Anatomical homeothermy • Part-time homeothermy • (combinations of any/all of the above) Behavioral Homeothermy • Seek shade/wet to cool off – Kangaroos lick their legs. Camels pee on them • Orient body to minimize radiation Behavioral Homeothermy • Seek sun/dry to warm up (basking) • Orient body to maximize radiation bathing burrowing Behavioral Homeothermy Behavioral Homeothermy • Seek sun/dry to warm up (basking) • Or maybe some wet heat! • Seek/conserve body heat huddling Sleep curled up Japanese macaque sitting in a hot spring Heyer 4 Homeostasis & Thermoregulation Physiological Homeothermy — endothermy & feedback loops • Negative feedback Æ Homeostasis Homeo stasis “same” “stay” • Dynamic Constancy (= Dynamic Equilibrium): – Fluctuate around set point. – Set point may be reset for new situations. Homeostatic Mechanisms Negative Feedback Loop •Negative feedback loops ÿIntrinsic — within an organ ÿExtrinsic — integrating multiple organs Negative Feedback: Room Thermostat Antagonistic Effectors Pairs of effectors with opposing actions provide much tighter control. Heyer 5 Homeostasis & Thermoregulation Endothermic Effector Sets Endothermic Effector Sets 1. Heat producer: metabolic heat, – esp. from muscle 2. Heat exchanger: integument system 3. Heat convection between producer & exchanger: circulatory system * In addition to these effectors, need nervous & endocrine systems to integrate & coordinate actions Redundant effectors allow stronger responses to stronger deviations. Heat Production — muscle activity Heat Production — muscle activity • Some insects may fly inefficiently, just to generate enough heat to keep warm • Shivering : “ineffective” muscle contractions Heat Production — another effector? Heat Exchange — integument • Non-shivering thermogenesis: uncoupling ATP production so respiration yields more heat per unit fuel Food energy + O 2 Cell respiration CO2 + H2O + energy • Skin : – Epidermis: Pigments reduce/enhance radiant absorption – Dermis: produce hair or feathers Æ trap air space • Ø convection, conduction, & evaporation • Pigments further reduce/enhance radiant absorption – Hypodermis: ADP Cell work ATP HEAT • Blood vessels regulate convective loss of metabolic heat • Adipose tissue insulates from conductive transfer Esp . in brown fat of newborn & hibernating mammals brown fat Heyer white fat 6 Homeostasis & Thermoregulation Heat Exchange — integument Heat Exchange — integument • Sea otters — problem: small; no blubber; live in cold water • Increase insulation by increasing fat layer — blubber • Increase insulation by increasing hair density • Increase heat production by increased metabolic rate Hair Density of 3 Mammals Average Daily Schedule for Sea Otter Grooming Hairs per Square cm 180000 160000 140000 Eating 120000 Sleeping 100000 80000 Grooming 60000 40000 20000 Metabolism Must eat 25% of body weight in food per day! 0 Human Rat Sea Otter Like a 150 pound person having to eat 125 hamburgers per day!!! Animal Insulation Heat Exchange — integument • Polar bears — large, thick fat layer & fur • Black skin absorbs radiant energy — fur acts as light guide to direct sunlight to skin while appearing white • High calorie diet to support increased metabolic rate Heat Exchange — integument • Evaporative cooling: evaporating water absorbs much heat energy • Wet epidermis cools much faster 540 calories/g water evaporated • IF you can afford the water loss! sweating panting Negative Feedback: Body Thermostat Heyer 7 Homeostasis & Thermoregulation Blood flow & heat transfer Blood flow & heat transfer • Counter-current exchangers: • Radiators: Increase cooling by vasodilation to long, thin appendages Blood flow & heat transfer • Counter-current exchangers: Decrease heat loss — reclaim it in returning blood flow • Marine mammals, arctic homeotherms, sloths Decrease heat loss — reclaim it in returning blood flow • Marine mammals, arctic homeotherms, sloths Blood flow & heat transfer • Counter-current exchangers: Decrease heat loss — reclaim it in returning blood flow • Marine mammals, arctic homeotherms, sloths Baleen whales lose heat through their tongues Rete mirabile Blood flow & heat transfer • Counter-current exchangers: • Also in large-body, active, endothermic poikilotherms (lamnid sharks, tunas, billfish) • TB not constant, but swimming muscles, brain & eyes may be 10 –15 ° warmer than ambient ocean temp Heyer Dynamic Constancy – Fluctuate around set point. – Set point may be reset for new situations. • ØTB at times of low activity (sleep) • ↑ TB to fight infection (fever) 8 Homeostasis & Thermoregulation Part-time Homeothermy Part-time Homeothermy • Using physiological homeothermy only under certain conditions • Arabian oryx — when water is available • Using physiological homeothermy only under certain conditions • Mouse Opossum — when food intake is sufficient Poikilothermy When Water Rare Avoid water loss, adjust physiology, behavior - seek shade Homeothermy When Active Homeothermy When Water Present Sweat, Pant, etc. Poikilothermy When Inactive Turbinal evaporation cools 45 °C (113 °F) systemic blood to 41 ° before entering brain. •Body Temp ~ Outside Temp •Torpor Part-time Homeothermy Part-time Homeothermy • Using physiological homeothermy only under certain conditions • Long-term torpor = hibernation • Hummingbird – Small body = high metabolism – Can ’t store enough energy overnight • Belding ground squirrels – Torpor: lower metabolic rate and T B Endothermic-Homeotherms vs. Ectothermic-Poikilotherms Endothermic-Homeotherms vs. Ectothermic-Poikilotherms — relative advantages — relative advantages Endo Hypothermia, Death Freezing Ambient Temperature Hyperthermia, Death Boiling General Rules : Endotherms use more O 2 /metabolism as outside temp Ø Ectotherms use less O2 /metabolism as outside temp Ø Heyer Breathing Rate/O 2 Use g in nt Pa Ecto g in er iv Sh g in er iv Sh Breathing Rate/O 2 Use Ecto g in nt Pa Endo Hypothermia, Death Freezing Ambient Temperature Hyperthermia, Death Boiling Thermal Neutral Zone — temperature range requiring the lowest metabolic rate in endotherms 9 Homeostasis & Thermoregulation All Living Things Require Energy… Endothermic-Homeotherms vs. Ectothermic-Poikilotherms — relative advantages Endothermic- EctothermicHomeotherms Poikilotherms balance energy needs with energy production Advantages Activity level independent of environmental temp Low food energy demands Disadvantages High food energy Activity level dependent on environmental temp Selection Favored in low nutrient environments demands …but there are major tradeoffs in strategies for making/spending that energy Metabolic Rates v Alligator can match human energy output for 1 second; v slows down after that. Favored in high nutrient environments Adjusting to a new environment • Aclimatization: an organism gradually D metabolic rate, thickness of fat/fur/feathers; enzyme expression; etc. – Aclimation: adjusting to an artificial change • Adaptation: a population shifts its characters over many generations – Bergmann’s Rule: species father from the equator have larger body mass (cooler climate Æ Øsa/v ratio) – Allen’s Rule: colder climates Æ shorter appendages; warmer climates Æ longer Heyer 10 ...
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This note was uploaded on 09/02/2011 for the course BIOL 6a taught by Professor Staff during the Fall '10 term at DeAnza College.

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