Transport/Reaction Processes in Biology and Medicine

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Lightfoot, Edwin N.
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Transport Phenomena, and particularly mass transfer and chemical reaction, govern a great variety of physiological and pathological processes, and they supplement in a non-trivial way genetic factors in both organism development and species evolution. For humans and other mammals, of primary interest here, the body may in fact be viewed as a complex and hierarchical transport/reaction system supplying the needs of genes and protecting them from the environment. Four major organs, skin, gut, lungs, and kidneys, interact directly with the external environment and, via an extremely complex series of transport processes, with other organs, organelles, all body cells and ultimately their genes. These processes range from relatively familiar convective transport in blood and pulmonary gases to very complex forced diffusion mechanisms at the cellular and sub-cellular levels. Our purpose here is to suggest effective bases for modeling and manipulating selected subsystems of living organisms, and it must be recognized at the outset that a complete description is impossible. Just a glimpse at an atlas of human anatomy will make this clear. Our approach is to suggest approximations simple enough to be soluble, testable and hopefully sufficiently detailed for the purposes at hand – and these purposes can vary greatly. There is thus a need for multi-scale models. There is also a strong historical component to evolution. This is why Himalayan climbers struggling at the very limits of their respiratory systems can sometimes look up and see migrating geese flying strongly far over their heads. The geese have inherited the pulmonary systems of dinosaurs. In addition biological systems, though they must obey the equations of change, can employ a wider range of boundary conditions than permitted by engineering texts. Thus while the rising sap in tall trees must follow Poiseuille’s law it can operate at negative pressures.
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