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Homeostasis

Homeostasis. Chapter 2. Definitions. Ionoconformer : Animals with the same ion concentration of extracellular fluid as external environment Ionoregulators : Animals that to some extent regulate the ion composition of extracellular fluid

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Homeostasis

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  1. Homeostasis Chapter 2

  2. Definitions • Ionoconformer:Animals with the same ion concentration of extracellular fluid as external environment • Ionoregulators: Animals that to some extent regulate the ion composition of extracellular fluid • Osmoconformers: Animals with the same osmolarity of extracellular fluid as external environment • Osmoregulators: Animals that to some extent regulate the osmotic concentration of their body fluids

  3. Homeostasis & Regulation • Regulation:The active maintenance of a physiological variable at a specific value, the setpoint. • Homeostasis:The occurrence of a constant interior environment with respect to physiological variables (e.g., osmo- and ionoregulation, blood gasses, blood pressure, temperature) Note: regulation is not a precondition for homeostasis and regulation does not imply perfect homeostasis

  4. Tolerance Quantified by measuring survival at different levels of a chemical or other stressor LD50 (mol/kg): Lethal dose for 50% of the population LC50 (mol/L): Lethal concentration for 50% of the population (applicable to aquatic organisms) Resistance Quantified by measuring the time to death after administration of a chemical or other stressor at a level that is beyond the tolerance range. LT50 (h): Lethal time (or tolerance) for 50% of the population Tolerance & Resistance

  5. Individuals and Populations may Alter their Ranges of Tolerance and Resistance • Acclimatization: Physiological readjustment to a change in the natural environment • Acclimation: Physiological readjustment to a change in laboratory conditions (or by anthropogenically induced changes in the natural environment) • Adaptation: Adjustment at the genetic level to specific environmental conditions. Often brought about by natural selection

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