Energy and Thermoregulation

Maintaining internal environments: Challenge for all living environments

Regulators: use internal control mechanisms to regulate internal change in the face of fluctuations in the external environments. Conformers: allows internal environment to conform to external changes (for a particular environmental variable)

Regulating and conforming are extremes of a continuum: Organisms may conform to some environmental factors and regulate others. e.g. fish – thermoconformers, osmoregulators.

Homeostasis (steady state): Maintaining relatively steady internal environment even when external environment changes significantly. Dynamic equilibrium: external factors try to change internal environment, internal control mechanisms oppose such changes.  Body temperature: 37 o C  pH: 7.4  blood glucose: 90mg/100mL of blood

Mechanisms of homeostasis:  Set point: the desired temperature (variable)  Stimulus: fluctuations in the variable  Sensor: detect stimulus and triggers an appropriate change  Response: activity that helps return the variable to the set point

Home heating system as an example of homeostasis

Do you see the machanism of homeostasis here ?

Negative feedback loop: response that reduces the stimulus. (exercise and sweting) Positive feedback loop: responses amplify the stimulus (labor)

Regulated changes of setpoint: e.g. temperatures change when asleep and awake, hormone levels in women’s menstrual cycle Acclimatization: change in normal range of homeostasis in response to internal environment. e.g. increased blood flow and red blood cell production Acclimatization is not adaptation – acclimatization is temporary; adaptation is natural selection working on a population over several generations.

Homeostatic process for thermoregulation: Essential to maintain internal temperatures within “tolerable” range.  Enzymes have narrow optimal temperature range.  10 o C change in temperature reduces enzyme activity 2 to 3 fold  Proteins start to denature and loose activity

Endothermy: warm themselves by heat generated by metabolism (birds and mammals). Have ways of warming and cooling their bodies. Consume more food than ectotherms Ectothermy: gain their heat from external sources (amphibians, lizards, snakes, turtles, fishes). Mostly change body temperature by behavior. Endotherms may have some ectothermic behavior. Two strategies are not mutually exclusive.

Poikilotherm: Animal whose temperature varies with environment Homeotherm: Has a relatively constant body temperature Common misconception: poikilotherms are coldblooded; homeotherms are warmblooded.

Balancing heat loss and gain: Heat exchange is regulated by four physical processes:  Conduction  Convection  Radiation  Evaporation

Thermoregulatory organ: major role played by the integumentary system (skin, hair, nails, fur, scales, claws)

Theromregulatory adaptations:  Insulation  Circulatory adaptations  Evaporative loss of heat  Behavioral adaptations  Adjusting thermogenesis

Theromregulatory adaptations:  Insulation  Circulatory adaptations  Evaporative loss of heat  Behavioral adaptations  Adjusting thermogenesis

Insulation: Prevent flow of heat between animal and environment Hair, feather: traps air and insulates, raising hair traps more air Goose bumps Some animals ooze oil into their hair to prevent them from getting wet

Theromregulatory adaptations:  Insulation  Circulatory adaptations  Evaporative loss of heat  Behavioral adaptations  Adjusting thermogenesis

Circulatory adaptations: Regulate blood flow near body surface and maintain core body temperature Vasodialation: nerve signals relax muscles of the superficial blood vessel walls, increased blood flow to the surface, heat directed to the skin, increase in surface temperature, heat dissipated by radiation, example: jack rabbits ears Vasoconstriction: Diameter of superficial blood vessels decrease, reduces blood flow to the surface and prevents heat loss.

Circulatory adaptations contd…. Countercurrent exchange: arrangement of tissues and blood vessels in a particular way that maximizes heat exchange. Example: goose and dolphin;

Vein Artery Skin Capillary network within muscle Blood vessels in gills Heart Artery and vein under the skin Dorsal aorta Great white shark

…..also helps maintain core body temperature in essential tissues, like flight muscles

Bluefin tuna Body cavity 31° 29° 25° 27° 23° 21°

Theromregulatory adaptations:  Insulation  Circulatory adaptations  Evaporative loss of heat  Behavioral adaptations  Adjusting thermogenesis

Evaporative heat loss: Water evaporates considerable heat during evaporation Panting in dogs Sweating Fluttering of pouch at the base of the mouth

Theromregulatory adaptations:  Insulation  Circulatory adaptations  Evaporative loss of heat  Behavioral adaptations  Adjusting thermogenesis

Behavioral responses: Migration Body orientation Hibernation Bathing Huddling Storing high calorie food (honey)

Theromregulatory adaptations:  Insulation  Circulatory adaptations  Evaporative loss of heat  Behavioral adaptations  Adjusting thermogenesis

Adjusting thermogenesis:  Shivering thermogenesis: heat production as a result of increased muscle activity  Nonshivering thermogenesis: some specialized chemical reactions results in heat production instead of ATP in mitochondria

Adjusting thermogenesis contd…  Some ecothermic animals can do some endothermic regulation (egg incubation by Burmese python, resulting from spasmodic muscle contraction)

Adjusting thermogenesis contd…  Some insects perform “warm-up” preflight shivering to get critical muscles warmed up

Acclimatization in Thermoregulation: Thicker coat during winter Enzymes with different optimal temperatures but same function Cells with antifreeze compounds

Physiological thermostats – temperature regulation in humans:

Fever: increase in set point of body temperature in the hypothalamus, for instance – response to infections  Fever has some defensive functions  Fever is observed in endotherms  Ectotherms have behavioral adaptations that function like development of fever, during an infection

Bioenergetics: Related to animal’s size, activity, environment Determines food need Overall flow and transformation of energy in an animal

Energy allocation and use: Animals obtain energy for various activities from food Food is digested in the body by enzymatic hydrolysis Digested food generates ATP as a result of cellular respiration ATP is used for biosynthesis, growth, repair, reproduction etc. and for generating heat

Quantifying energy use: Metabolic rate: sum of all energy requiring biochemical reactions over a given time interval. Can be measured by heat production, carbon dioxide production, food consumption etc.

Basal Metabolic Rate (BMR): Minimal metabolic rate of a nongrowing endotherm at rest, in an empty stomach, at comfortable temperature with no generation or shedding of heat.  Human males – 1,600 to 1,800 kcal (C) per day  Human females – 1,300 to 1,500 kcal per day

Standard metabolic rate (SMR): metabolic rate of a fasting nonstressed ectotherm at a particular temperature.  Alligator – 60 kcal per day

Maximum metabolic rate (MMR): Highest rate of ATP use; is inversely related to the duration of the activity.

Size and metabolic rate: Relationship between metabolic rate and body mass is constant across a wide range of sizes and forms Metabolic rate is roughly proportional to the body mass, to the ¾ power (m ¾ ) The reason for this is not yet known

Energy budgets:

Torpor, Hibernation, Energy conservation: Physiological state of low activity, low metabolism, body temperature drops, allowing the animal to save energy and avoid situations where it is more vulnerable Hibernation is long term torpor.

Small animals with higher metabolism go into torpor;  bats torpor during the day,  hummingbirds at night.

Certain squirrels show prolonged torpor with brief arousals in winter.