Thermoregulation Biology Stage 3 Chapter 15 Pages

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Keywords Thermoregulation Ectotherms Endotherms Metabolic heat Heat exchange Insulation ◦ Brown fat Surface area-to- volume ratio Temperature gradient Physiological responses Piloerection Vasodilation Vasoconstriction Evaporating ◦ Sweating ◦ Panting

Ectotherms All animals, other than birds and mammals, are ectotherms (‘outside heat’) They do not generate their own heat but have a body temperature the same as that of the environment, whether it is hot or cold They are often inactive during winter because their cells function so slowly at low temperatures

Ectotherm Ectotherms do alter their behaviour to vary their internal temperature They lie in the sun to warm up or burrow underground to stay cool Some animals (some fish & insects) use the heat produced by their metabolism or by muscular activity ( metabolic heat ) to maintain a body temperature higher than the environment

Endotherms Endotherms (birds & mammals) generate and maintain their own body heat Maintaining body heat is called thermoregulation If the environment is colder, the internal temperature is maintained by increasing heat production and reducing heat loss If the environment is warmer, the internal temperature is maintained by decreasing heat production and increasing heat loss

Endotherms Thermoregulation involves: 1.controlling metabolic heat production 2.regulating heat exchange with the environment

Controlling heat production Heat production is controlled through increasing or decreasing metabolic activities Metabolic heat can be generated by:  Increasing muscle activity (shivering)  Increasing cellular activity (brown fat)  Increasing rates of cellular metabolism The hypothalamus is the regulatory centre in the brain It signals to increase or decrease metabolic activities It also regulates physiological responses to maintain homeostasis Heat sensors or thermoreceptors in the body relay information to the hypothalamus

Regulating heat exchange The rate of heat exchange with the environment depends on: 1. Insulation 2. Surface area-to-volume ratio 3. Temperature gradient between the body and the environment 4. Adaptive behaviours INSULATION Fur & feathers Trap layer of warm air next to skin Fur and feathers only good insulators when dry Piloerection – tiny muscles cause hair to lift away from skin increasing the thickness of the trapped air layer Layer of fat Brown fat – hibernating animals Large amount of mitochondria

Regulating heat exchange SURFACE AREA-TO- VOLUME RATIO Smaller animals have a larger surface area-to- volume ratio than larger animals They therefore require relatively more food to maintain a higher metabolic rate ADAPTIVE BEHAVIOURS Endotherms can vary their behaviour to maintain optimum body temperature TEMPERATURE GRADIENT Regulation involves: Circulatory changes ◦ Vasodilation ◦ Vasoconstriction Counter-current arrangements of blood vessels Loss of heat through evaporation ◦ Sweating ◦ Panting

Countercurre nt heat exchange

Rising body temperature

Falling body temperature

Feedback systems Negative feedback systems have a number of common features: The stimulus is the change in the environment The receptor detects the change The modulator is a control centre responsible for processing information The effector carries out a response counteracting the effect of the stimulus (or change in the environment)

Behavioural responses to change in external temperature

Response to high core temperature Effector Core temperature ˃ 37 o C Thermoreceptors Hypothalamus Surface blood vessels Sweat glands Vasodilation Sweating Reduced heat production & increased heat loss returns core temperature to normal Stimulus Modulator Control centre Response Negative feedback Receptor

Response to low core temperature Effector Core temperature <37 o C Thermoreceptors Hypothalamus Surface blood vessels Skeletal muscles Vasoconstriction Piloerection Shivering Reduced heat loss & Increased heat production returns core temperature to normal Stimulus Modulator Control centre Response Negative feedback Receptor