L18_homeostasis_F09_Handout - Homeostasis -1- EEMB 106...

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Homeostasis -1- EEMB 106 Homeostasis I. Thermoregulation Ectothermy : (“cold-blooded”), reliant upon external heat advantage: low metabolic costs (requires less energy, less food) disadvantage: cannot live/function well in extremes (especially cold) Endothermy: (“warm-blooded”), produce own heat disadvantage: high metabolic costs (requires more food, leaves less energy for reproduction, growth, etc. advantage: biochemical reactions become more efficient, fish can utilize wider thermal ranges A. Heat conservation 1. from rete near large swimming muscles, e.g. tunas, sharks 2. from rete on liver – warms internal organs 3. some fish warm parts of central nervous system (esp. brain and eyes): a) circulatory modifications, e.g. retes near eyes b) special heat producing tissues, e.g. billfish with “brown fat” – non- contracting muscle tissue – to heat eye B. Coping with temperature fluctuations 1. Behavioral – move to locations with better thermal environment 2. Physiological a) switch genes on/off: e.g., heat shock proteins b) increase enzyme concentration to compensate for reduced activity c) isozymes: different gene loci that produce enzymes that operate at different temperatures
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L18_homeostasis_F09_Handout - Homeostasis -1- EEMB 106...

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