Thermoregulation

Thermoregulation

Maintenance of temperature by balancing heat influx and efflux

Heat can be gained or lost through

-Conduction

-Convection

-Radiation

Heat can be lost through

Evaporation

Heat can be gained through 

Metabolism

Conduction

Transfer of kinetic energy between two stationary objects in direct physical contact

Example of conduction

Putting hand on table where molecules are moving at different rates and the KE gets transferred through physical contact 

Heat transfer via conduction:

F=A (T₁-T₂)/i

F=rate of heat transfer

A= area of contact

T₁ and T₂ = temperature gradient

i=insulation factor

Effect of insulation

More insulation= slower rate of heat transfer

Convection

Transfer of kinetic energy involving fluid flow

Example of convection

Placing hand in moving water in a river where water continues to be replaced as cold

Characteristics of convection

-Warm (or cold) objects can generate their own convection

-Greater temperature gradient for heat transfer between an object and fluid than with two stationary objects

Radiation

Transfer of energy through emission of electromagnetic radiation (radiant heat)

Example of radiation

Radiation heat transfer from fire or sun (environment) to humans

Characteristics of radiation

-All objects emit radiation above 0K

-Most objects in our environment emit in the IR range

Evaporation

Transfer of heat by liquid phase change 

Example of evaporation

Sweat; energy absorbed to make phase transition is energy that is carried away from our body

Metabolism

Internal location for heat influx where heat is a byproduct

Negative Feedback Loop with Temperature

Regulated Variable: body temperature

Control Center (Hypothalamus): body’s thermostat that has set point

Effector (Muscle Shivering): produced heat through burning of ATP

Feedback response if body temperature drops

Respond in a way that increases heat influx and decreases heat efflux: low blood flow to skin, high shivering (muscles), high basal met. rate (sustained situation)

Feedback response if body temperature rises

Respond in a way that decreases heat influx and increases heat efflux: high sweating, high blood flow to skin, low basal met. rate (sustained situation)

Basal metabolic rate

# of calories your body burns at rest to perform basic cellular activity like breathing, circulation, and cell production

Relationship of blood flow and insulation

More blood flow that you have at the surface of your body, the more limited it is to be insulated. 

Physiological regulation

Advantages: greater ability to tolerate a range of conditions and greater capacity for activity in a range of conditions

Disadvantages: energetically expensive and requires evolved regulatory systems

Environmental conformation

Body temperature same as surrounding environment

Behavioral regulation

Body regulation at certain times a day that leads to lower energetic costs but depends on a warm environment 

Example of behavioral regulation

Thermoregulation using environmental heat in many reptiles like lizards who stay in burrow during the night and shuttle between sun and shade during the day

Categories of temperature regulation in animals

Major source of heat: Endotherms and Ectotherms

Variability in body temperature: Homeotherms and Heterotherms 

Endotherms and Ectotherms

Endotherms produce substantial body heat by themselves whereas ectotherms are at the mercy of the environment

Homeotherms and heterotherms

Homeotherms have fairly constant body temperature whereas heterotherms see substantial variation 

Classification of thermoregulation levels

-Endotherms and Homeotherms: birds and mammals

-Endotherms and Heterotherms: mole-rats

-Ectotherms and Heterotherms: freshwater fish and terrestrial invertebrates 

-Ectotherms and Homeotherms: marine fish and invertebrates

Hibernation or torpor

Drop in temperature and metabolic rate to conserve energy

Adaptations to reduce heat efflux

-Reduce surface area

-Increase insolation: trap still air in fur/feathers for terrestrial environment or fat in aquatic environments

-Decrease temperature differential through torpor, hibernation, countercurrent exchange

Countercurrent exchange

Transfer of heat between fluid flowing in opposite directions where warm arterial blood flows next to cooler venous blood