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Achieving Homeostasis: Understanding Tolerance, Resistance, and Adaptation

Explore the concepts of homeostasis, tolerance, resistance, and adaptation in regulating physiological variables. Learn the principles of ionoconformers, ionoregulators, osmoconformers, and osmoregulators in maintaining internal balance. Discover how individuals and populations adjust to environmental changes through acclimatization, acclimation, and adaptation.

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Achieving Homeostasis: Understanding Tolerance, Resistance, and Adaptation

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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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