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Review How do the immune systems and endocrine glands help to maintain homeostasis
Apply Concepts Describe how the circulatory and endocrine systems of migrating wildebeest help maintain homeostasis
Review Define ectoderm and endotherm

28.4 Homeostasis

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Control of internal conditions
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Essential to an organism’s survival.

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Digestive, respiratory, circulatory, excretory, nervous, muscular, and skeletal systems are all interconnected and work together to maintain homeostasis.

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Regulate body activities by releasing hormones into the blood.

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Requires three components:
 Source of heat
 Way to conserve heat when necessary
 Method of eliminating excess heat when necessary.

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Regulate body temperature primarily by absorbing heat from, or losing heat to, their environment
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Most reptiles, invertebrates, fishes, and amphibians.

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Relatively low metabolic rates when resting- don’t generate much heat
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Lack effective body insulation so body heat is easily lost
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Warm up by basking in the sun and often use underground burrows.

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Regulate body temperature, at least in part, by using heat generated by its body
Birds and mammals
High metabolic rates that generate heat, even when they are resting
Conserve body heat primarily with insulating feathers, fat, fur, or hair
Reduce body temperature by sweating and panting.

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Ectotherms need much less food than similar-size endotherms need
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Ectothermy is a more energy-efficient strategy in consistently warm environments
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Large ectotherms have trouble in cold temperatures trying to warm up.

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Evidence suggests that at least some dinosaurs were endotherms
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Current evidence suggests that endothermy has evolved at least twice among vertebrates
 Once in the bird line
 Once for mammals.