Thermoregulation - ectotherms and endotherms

Cell signalling

• the coordination and hormonal systems at a cellular level to maintain the internal environment

• One cell releases a chemical that has an effect on another (target) cell

  • locally = synapses

    • neurotransmitters at a synapse

  • large distances = hormones

    • ADH in humans

    • auxins in plants

Homeostasis

• the maintenance of a stable equilibrium in the internal environment

• receptors

  • detect a change in either the internal or external environment

• effectors

  • muscles or glands that bring about a change in response to a syllabus

Negative feedback

• sensory receptors detect a small change in the environment and effectors return the environment to the usual conditions

Positive feedback

• sensory receptors detect a small change in the environment and effectors are stimulated to increase that response

Thermoregulation

• constant core body temperature helps maintain optimum enzyme activity in the body

  • too low and metabolism is too slow

  • too high and enzymes denature

Ectotherms

• all invertebrates, reptiles, fish and amphibians

• cannot control their body temperature using their body metabolism

• have a body temperature the same as their environment

• ectotherms that live in water have a more constant body temperature

• if the temperature is too low - metabolic reactions in ectotherms are too slow for them to be active

• use a range of behavioural and physiological responses to control their temperature

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Warming responses of ectotherms

• black

  • absorbs more radiation

• sideways to sun

  • larger SA exposed to heat of the sun

• increased HR

  • increases metabolic rate to produce more heat

• inflates its body

  • increased SA to absorb radiation

• lies on sand

  • absorbs heat directly from sand

Cooling responses of ectotherms

• Deflates body

  • less SA to absorb heat

• pale grey

  • absorbs less radiation

• holds itself away from sand

  • absorbs less heat from sand

• decreased HR

  • lower metabolic rate

• opens mouth and pants

  • increases heat loss

Advantages and disadvantages of being ectothermic

• Advantages

  • less food used in respiration

  • can survive longer without food

  • greater proportion of energy can be used for growth

• disadvantages

  • less active in cooler temperatures

  • during winter may not be capable of activity so must have sufficient stores of energy to survive over winter

Endotherms

• generate their own heat from their metabolic reactions

  • respiration is exothermic

• the core temperature is maintained within a narrow range

• the peripheral temperature is allowed to vary

• temperature is controlled by a balance between heat generated and heat lost to the environment

Hypothalamus

• controls homeostasis

• contains receptors that monitors the blood

• receives impulses from other receptors

• sends nerve impulses to effectors

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