A model is an object of imitation, something that accurately resembles something else, a person or thing that is the likeness or image of another.4 Prometheus, who has been deigned by poets to have first formed Man, formed a model from water and earth and then stole fire from the sun to animate the model.5 An animal model is thus an animated object of imitation in the image of humans (or other species), used to investigate biological or pathobiological phenomena.
A laboratory animal model describes a biological phenomenon that the species has in common with the target species.6 A more accurate definition has been given by Held on the basis of Wessler's original definition:7 "a living organism in which normative biology or behavior can be studied, or in which a spontaneous or induced pathological process can be investigated, and in which the phenomenon in one or more respects resembles the same phenomenon in humans or other species of animal." What is generally understood by the term "animal model" is modeling of humans. It is not the image of the used animal that is the focus of research but the analogy of the physiological behavior of this animal to our own (or another) species. It would thus be more correct to refer to animals as "human models" in this context. Laboratory animal science, comparative medicine, and animal experiments are indeed much more about humans than about any other animal species.8
The significance and validity with respect to usefulness in terms of "extrapolatability" of results generated in an animal model depend on the selection of a suitable animal model. A good knowledge of comparative anatomy and physiology is an obvious advantage when developing an animal model. Animal models may be found throughout the animal kingdom, and knowledge about human physiology has been achieved in species far removed from the human in terms of evolutionary development. A good example is the importance of the fruit fly for the original studies of basic genetics. Animal models are used in virtually every field of biomedical research, as reflected in the chapters of this book.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.