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Links to the current specifications

AQA 3.5.1 Stimuli, both internal and external, are detected and lead to a response.3.5.1 Co-ordination may be chemical or electrical in nature.3.5.4 Homeostasis is the maintenance of a constant internal environment.3.5.5 Negative feedback helps maintain an optimal internal state in the context of a dynamic equilibrium. Positive feedback also occurs.

Edexcel Topic 7 – Run for your life: 15. Explain the principle of negative feedback in maintaining systems within narrow limits.16. Discuss the concept of homeostasis and its importance in maintaining the body in a state of dynamic equilibrium during exercise, including the role of the hypothalamus and mechanisms of thermoregulation.

OCR 4.1.1 Communication4.1.3 Hormones5.4.2 Animal responses

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Thermoregulation in endotherms

Endotherms generate most of their heat metabolically. As they are warmer than their environment they tend to lose body heat to their surroundings.

Adaptations for heat conservation include:

Insulation – insulating layers of fat, fur or feathers to prevent heat loss.

Metabolism – metabolic rate can be varied to generate more or less heat.

Endotherms also use their skin to vary their rate of heat loss and maintain a constant core body temperature.

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Thermoregulation in humans

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Hyperthermia and hypothermia

Prolonged exposure to high temperatures can lead to hyperthermia. The body’s core temperature rises above 41°C causing its thermoregulatory mechanisms to break down.

If the body’s core temperature falls below 35°C a person may suffer from hypothermia. Again the body’s thermoregulatory mechanisms fail and positive feedback occurs leading to a further decrease in temperature.

When this happens, positive feedback occurs and the person’s body temperature can spiral out of control. A core body temperature of 43°C and higher usually causes death.

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Physiological thermoregulation

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Thermoregulatory control system