Emergence of Oscillatory Dynamics
Besides their systems nature, as described in the preceding chapters, the single most characteristic feature of a living organism is the self-sustained activity it displays in the form of a wide variety of different oscillatory processes [25, 9, 22, 23].
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Emergence of Oscillatory Dynamics Jakob L. Laugesen and Erik Mosekilde
It doesn’t move - it is probably dead. One of the most characteristic features of a living organism is its sustained activity as revealed through the many different rhythmic processes it displays.
4.1 The Role of Instabilities and Oscillatory Dynamics Besides their systems nature, as described in the preceding chapters, the single most characteristic feature of a living organism is the self-sustained activity it displays in the form of a wide variety of different oscillatory processes [9, 22, 23, 25]. The respiratory cycle and the beating of the heart are generally recognized as internally generated oscillatory processes that first of all serve to pump oxygen from the atmosphere to the various tissues and cells of the body. The circulating blood, of course, also serves to supply the cells with the nutrients they need, to remove carbon dioxide and other metabolic bi-products, and to maintain hormonal communication between the various organs. The beating of the heart and the ventilation are directly related to our distinction between the living and the dead. We check for the pulse and we check for breathing. The menstrual cycle represents another well-known rhythm that serves as a clock to organize the sequence of hormonal processes required to prepare the organism for
J.L. Laugesen () E. Mosekilde Department of Physics, Technical University of Denmark, Fysikvej 309, DK-2800 Lyngby, Denmark e-mail: [email protected]; [email protected]
E. Mosekilde et al. (eds.), Biosimulation in Biomedical Research, Health Care and Drug Development, DOI 10.1007/978-3-7091-0418-7 4, © Springer-Verlag/Wien 2012
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J.L. Laugesen and E. Mosekilde
a new ovulation, and investigations performed during the last decades have revealed a great variety of additional biological rhythms with periods ranging from fractions of a second to several hours or even day. Many hormonal systems, for instance, are unstable and operate in an episodic or oscillatory mode [6, 17, 18]. As described in Chap. 3, such a pulsatile secretion has been observed for insulin in normal young men during constant enteral nutrition as well as during constant glucose infusion [31, 33], and the secretion of both growth hormone [4] and luteinizing hormone in man [30] displays similar 2–5 h (so-called ultradian) rhythms. Moreover, it is evident that the biological effect of certain hormones can be increased if they are administered in a rhythmic fashion [5], and that disruption of normal hormonal rhythms, or the generation of new rhythms, can be associated with specific states of disease [9]. By regulating the excretion of salts, water and metabolic end products, the kidneys play an important role in maintaining a suitable environment for the cells in the body. In particular, the kidneys regulate the plasma osmolality and the proportion of the various blood solutes and, by regulating the excretion of water and salts, the kidneys control the extracellular fluid volume and, to some
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