Homeostasis & Thermoregulation

The Body’s Internal Environment The Body’s Internal Environment

A Dynamic Constancy

Integration & regulation: “the whole is greater than the sum of its parts”

Homeostasis: maintaining a Why is Homeostasis so important?

Optimal temperature for Optimal temperature for constant, optimal internal Among other things… typical human enzyme enzyme of thermophilic (heat-tolerant) environment • Proteins bacteria – including the enzymes and other molecular machines that run Rate of reaction 0 20 40 80 100 everything, Temperature (Cº) • are very sensitive to (a) Optimal temperature for two enzymes deviations in conditions – Esp., temp & pH – D protein shape fi ∅ fx

Conformers & Regulators Conformers vs. Homeostasis?

• Conformers: allow • How can they be homeostatic internal environment to and conforming? conform to external • Live in a stable environment • Regulators: use control – At least with respect to the conformed variable mechanisms to maintain constant internal and/or environment despite • Be able to make new external variations versions of proteins for • Note: an organism may each variation be different for different – Requires larger genome variables – Transition to new condition – The same fish may be a otter & bass from same stream must be gradual enough to otter & bass from same stream thermoconformer and an allow sufficient expression of osmoregulator new proteins

Heyer 1 Homeostasis & Thermoregulation

For Example: Environmental Heat Transfer Thermoregulation • Radiation: radiant energy absorbed/rereleased as thermal • Conduction: direct transfer of thermal energy • Poikilotherm (variable temp): • Convection: thermal energy absorbed by medium • Heat of evaporation: evaporating water absorbs energy body temp (TB) varies with environment temp • 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

Cell respiration • Energy cannot Food energy + O2 CO2 + H2O + energy be created nor destroyed ADP Cell work ATP HEAT • Energy can be transformed • All energy Standard metabolic rate (SMR)— in poikilotherms: • Minimum metabolism to produce sufficient ATP for transformations running ion pumps (electrolyte gradients), heart & lose some ventilation muscle activity, etc. (sleeping/fasting) at energy as heat standard temp Basal metabolic rate (BMR)— in homeotherms: • SMR + energy demand to keep body warm

Metabolic Heat Production Metabolic Heat Production

Cell respiration Cell respiration Food energy + O2 CO2 + H2O + energy Food energy + O2 CO2 + H2O + energy

ADP Cell work ATP HEAT ADP Cell work ATP HEAT

Estimating metabolic rate: ↑cellular work (esp. muscle activity) Æ • Measure rate of ↑demand for ATP Æ – Net food energy consumption ↑ metabolic rate Æ Heat production – Oxygen consumption – Carbon dioxide production – Heat production

Heyer 2 Homeostasis & Thermoregulation

Once again, … Size Matters! Environment also matters! Conduction & Convection in Aquatic vs. Terrestrial — • Heat exchange with the environment is proportional to body surface area (x2) • Water absorbs heat energy 50–100x faster than does air! • Heat generation from metabolism is proportional with body mass (or volume = x3) • ↑x fi↑x3 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

• It’s near impossible for a small aquatic organism to be endothermic 0.6 • It’s near impossible for a large terrestrial organism to be ectothermic

Size & Environment Matter! Poikilotherms — toleration ≠ thriving Conduction & Convection in Aquatic vs. Terrestrial — • Water absorbs heat energy 50–100x faster than does air! Even if can survive D temps, do best in a small range

Marine iguanas of the Galapagos • ↑↑TBÆ↑stress & mortality • Juveniles & adult females feed on exposed intertidal alga • ØØTBÆØmetabolic rate & activity • Only large males have sufficient body mass to generate enough heat to forage underwater • Lizards — – Ø discrimination in T-maze tests

– D behavior: warm lizards flee; cool lizards threaten

Western fence lizard

Poikilotherms — Tolerating extreme cold 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 • Largest land animals in Antarctica are tiny mites & springtails — freeze quickly most of year; thaw quickly to scavenge seal castings in brief warm season tissues to lower freezing point • Frogs and others: • Synthesize ice-binding proteins to prevent ice crystals – ice on skinÆ adrenalin rush from growing 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 A frozen arctic wood toad

Heyer 3 Homeostasis & Thermoregulation

Behavioral Homeothermy Homeotherms • Live in a stable environment • Behavioral homeothermy or • Move with the constant conditions • Physiological homeothermy • Anatomical homeothermy • Part-time homeothermy • (combinations of any/all of the above)

Behavioral Homeothermy Behavioral Homeothermy • Seek shade/wet to cool off • Seek sun/dry to warm up (basking) – Kangaroos lick their legs. • Orient body to Camels pee on them maximize radiation • Orient body to minimize radiation

bathing

burrowing

Behavioral Homeothermy Behavioral Homeothermy • Seek sun/dry to warm up (basking) • Seek/conserve body heat • Or maybe some wet heat! huddling Sleep curled up

Japanese macaque sitting in a hot spring

Heyer 4 Homeostasis & Thermoregulation

Physiological Homeothermy — endothermy & feedback loops Homeo stasis “same” “stay” • Negative feedback Æ Homeostasis

• 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 & Thermoregulaon

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.

Negative Feedback: Body Thermostat

Heat Production — muscle activity Heat Production — muscle activity • Some insects may fly inefficiently, just to generate • Shivering: “ineffective” muscle contractions enough heat to keep warm

Heyer 6 Homeostasis & Thermoregulaon

Heat Production Heat Exchange — integument — another effector? • Skin: • Non-shivering thermogenesis: uncoupling ATP – Epidermis: Pigments reduce/enhance radiant absorption production so respiration yields more heat per unit fuel – Dermis: produce hair or feathers → trap air space • ↓ convection, conduction, & evaporation Food energy + O2 Cell respiraon CO2 + H2O + energy • Pigments further reduce/enhance radiant absorption – Hypodermis: • Blood vessels regulate convective loss of metabolic heat ADP Cell work ATP HEAT • Adipose tissue insulates from conductive transfer

Esp. in brown fat of newborn & hibernating mammals

brown fat white fat

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 180000 160000

cm 140000 Eating 120000 Sleeping 100000 Grooming Square 80000

per 60000 40000 Hairs 20000 Metabolism Must eat 25% of body 0 weight in food per day! Human Rat Sea Otter Animal Like a 150 pound person having to eat 125 hamburgers per day!!! Insulation

Heat Exchange — integument Heat Exchange — integument • Evaporative cooling: evaporating water absorbs much heat energy • Polar bears — large, thick fat layer & fur • Wet epidermis cools much faster 540 calories/g water evaporated • Black skin absorbs radiant energy — fur acts as light guide to direct • IF you can afford the water loss! sunlight to skin while appearing white • High calorie diet to support increased metabolic rate

sweating

panting

Heyer 7 Homeostasis & Thermoregulation

Blood flow & heat transfer Blood flow & heat transfer

• Radiators: Increase • ↑blood flow and/or ↑surface area → ↑ heat exchange cooling by vasodilation to long, thin appendages

Blood flow & heat transfer Blood flow & heat transfer • Counter-current exchangers: • Counter-current exchangers: Decrease heat loss — reclaim it in returning blood flow Decrease heat loss — reclaim it in returning blood flow • Marine mammals, arctic homeotherms, sloths • Marine mammals, arctic homeotherms, sloths

Rete mirabile

Blood flow & heat transfer Blood flow & heat transfer • Counter-current exchangers: • Counter-current exchangers: Decrease heat loss — reclaim it in returning blood flow • Marine mammals, arctic homeotherms, sloths • Also in large-body, active, endothermic poikilotherms (lamnid sharks, tunas, billfish)

• TB not constant, but Baleen swimming muscles, whales lose brain & eyes may be heat through 10–15° warmer than their tongues ambient ocean temp

Heyer 8 Homeostasis & Thermoregulation

Dynamic Constancy Part-time Homeothermy • Using physiological homeothermy only under certain conditions – Fluctuate around set point. • Arabian oryx — when water is available

– Set point may be reset for new situations. Poikilothermy When Water Rare Avoid water loss, • ↓T at times of low activity (sleep) adjust physiology, B behavior - seek shade • ↑ TB to fight infection (fever) Homeothermy When Water Present Sweat, Pant, etc.

Turbinal evaporation cools 45°C (113°F) systemic blood to 41° before entering brain.

Part-time Homeothermy Part-time Homeothermy • Using physiological homeothermy only under certain conditions • Using physiological homeothermy only under certain conditions • Mouse Opossum — when food intake is sufficient • Hummingbird – Small body = high metabolism – Can’t store enough energy overnight

Homeothermy When Active – Torpor: lower metabolic rate and TB

Poikilothermy When Inactive

• Body Temp ~ Outside Temp • Torpor

Part-time Homeothermy All Living Things Require • Long-term torpor = hibernation Energy…

• Belding ground squirrels balance energy needs with energy production

…but there are major tradeoffs in strategies for making/spending that energy

Heyer 9 Homeostasis & Thermoregulation

Endothermic-Homeotherms vs. Endothermic-Homeotherms vs. Ectothermic-Poikilotherms Ectothermic-Poikilotherms — relative advantages — relative advantages

Ecto Ecto Shivering Shivering Use Use 2 2

Panting Panting

Endo Endo Hypothermia, Hypothermia,

Breathing Rate/O Death Hyperthermia, Breathing Rate/O Death Hyperthermia, Death Death

Freezing Ambient Temperature Boiling Freezing Ambient Temperature Boiling General Rules: Endotherms use more O2/metabolism as outside temp↓ Thermal Neutral Zone — temperature range requiring the Ectotherms use less O2/metabolism as outside temp↓ lowest metabolic rate in endotherms

reproduction Endothermic-Homeotherms vs. thermoregulation

growth Ectothermic-Poikilotherms — relative advantages activity

basal

Sustained energy output (Joule) of a poikilotherm (lizard) and a homeotherm (mouse) as a function of core body temperature. The hometherm has a much higher output, Energy Budgets but can only function over a very narrow range of body temperatures.

Endothermic-Homeotherms vs. Ectothermic-Poikilotherms Adjusting to a new environment — relative advantages • Aclimatization: an organism gradually Endothermic- Ectothermic- Δ metabolic rate, thickness of fat/fur/feathers; Homeotherms Poikilotherms enzyme expression; etc. Advantages Activity level Low food energy – Aclimation: adjusting to an artificial change independent of demands environmental • Adaptation: a population shifts its characters temp over many generations Disadvantages High food energy Activity level demands dependent on – Bergmann’s Rule: species father from the environmental equator have larger body mass temp (cooler climate → ↓sa/v ratio) Selection Favored in high Favored in low – Allen’s Rule: colder climates → shorter nutrient nutrient appendages; warmer climates longer environments environments →

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