Intradisciplinary work
The anatomical and medical origins of physiology still are reflected in university courses and textbooks that concentrate on functional organ systems of animals; e.g., frog, dog, cat, and rat. The trend in physiology, however, is to emphasize function rather than structure; i.e., comprehensive functional specializations such as nutrition, transport, metabolism, and information have replaced earlier structural studies of organ systems. This trend can be explained in part by the fact that the analysis of an organ system typically involves studies at the levels of cells and molecules, and functional emphasis accommodates such studies better than the organ-system approach.
Early in the 20th century, the emphasis on cells as units of function resulted in a view that all physiology is essentially cell physiology and that all teaching therefore should pivot around the properties of cells. In later years successful analyses of cellular mechanisms involving synthesis, control, and inheritance led to similar emphasis at a new and more fundamental level, the molecules that comprise cells. The study of physiology now encompasses molecules, cells, organs, and many types of animals, including man. The comparisons resulting from such studies not only strengthen human physiology but also generate new problems that extend into evolution and ecology. Much of the impetus for comparative physiology has resulted from the economic or medical importance to man of parasites, insects, and fishes.
Most of the physiology of microorganisms and plants developed independently of animal physiology. The concept of comparative biochemistry provided the foundations for a physiology of microorganisms that extended beyond the parasitic forms that are of medical importance and resulted in recognition of the fundamental roles of microorganisms in the biosphere. Botanists and agriculturists explore the physiology of higher plants, but fundamental differences in the modes of life of animals and plants leave little common ground above the molecular and cellular levels. In a little-known textbook, Claude Bernard stated that there is only one way to live, only one physiology of all living things. The goal of general physiology is to abstract this single physiology from the physiologies of all types of organisms. Although common or general features usually are found at the cellular and molecular levels of organization, multicellular structures also are studied. Processes that underlie cell function are emphasized in an approach based on analyses in terms of physical and chemical principles.
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Areas of study
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Metabolism
In the late 19th century the principle of conservation of energy was derived in part from observations that fermentation and muscle contraction are essentially problems in energetics. Biological energetics began with studies that established the basic equation of respiration as: Fuel + oxygen ? carbon dioxide + water + heat.
It was realized that the heat produced in fermentation and the work performed during muscle contraction must originate in similar processes, and that fuel in the equation above is a source of potential energy. Early in the 20th century studies of animal calorimetry verified these concepts in man and other animals. Calorimetry studies showed that the energy produced by the metabolism of foodstuffs in an animal equals that produced by the combustion of these foodstuffs outside the body. After these studies, measurement of the basal metabolic rate (BMR) was used in the diagnosis of certain diseases, and data relating the composition of foodstuffs to their value as sources of metabolic energy were obtained.
Early in the 20th century it was established that measurable amounts of the carbohydrate glycogen are converted to lactic acid in frog muscles contracting in the absence of oxygen. This observation and studies of alcoholic fermentation confirmed that the energy for fermentation or muscle contraction depends on a series of reactions now known as glycolysis. In order to show that the conversion of glycogen to lactic acid could provide the necessary energy for muscular contraction, extremely delicate measurements of the heat produced by contracting muscles were required
