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[4] The Anatomy and Physiology of Nutrition Form follows function. —Louis Henri Sullivan (1856–1924) God is in the details. —Ludwig Mies van der Rohe (1886–1969) The above quotes, although not meant to refer to biological systems, illustrate the following important points about biological processes: on a macroscopic, microscopic, and molecular level we are built exactly to perform the functions of life. The details of how this all evolved, how it all works, and how it all fits together are where the real beauty is. The first point is stated in Mr. Sullivan’s astute observation. (Louis Henri Sullivan was an architect at the turn of the twentieth century, is considered by some to be the creator of the modern skyscraper, and was mentor to one of the great architects of the twentieth century, Frank Lloyd Wright.) What Sullivan meant by his statement, of course, is that buildings (and everything else) should be designed according to the purpose for which they are meant. This is a good idea. And as one studies life’s processes in finer and finer detail, the exquisite truth of this observation as it applies to biological systems becomes clear—the function that an object, animate or inanimate, is meant to perform by definition determines its ideal form, and vice versa. This brings us to the second quote. Although there is some controversy as to its origin, majority opinion generally attributes it to Ludwig Mies van der Rohe. Van der Rohe was also an architect, also a colleague of Frank Lloyd Wright, and while his observation was also meant to be interpreted in terms of artistic expression, it is equally applicable to the ultimately simple complexity of life. The fundamental point of the information in this chapter is this: everything about the structure and function of living organisms, down to the smallest detail, is perfectly adapted (engineered?) to do exactly what it is meant to do. So whether you believe in the Darwinian concepts of mutation and natural selection as the engineers of these forms and functions or adhere to the belief of intelligent design (and an intelligent designer), it is hard to deny the beauty and perfection of life. We have reviewed the basic biochemistry of life—how elements and energy 78 [] the crisis of nutrition are incorporated into organically accessible forms to be used by living organisms and how they can be internally transformed into usable energy and raw material for energy and biosynthesis. But those are only the basic steps at a cellular level. How do macroorganisms, such as ourselves, internalize, process, and assimilate the macronutrients and deliver them to the internal environment in utilizable forms? What are the physical and functional strategies that living organisms have evolved in order to do this effectively and efficiently? Anatomy and Physiology of Nutrition The anatomy of nutrition is the physical structure of the gastrointestinal tract, and the physiology of nutrition is the functional means by which we transform our food into usable form. For purposes of clarity we divide this discussion into two segments: the anatomy of the gastrointestinal tract followed by the physiology, which we then discuss in terms of the two separate processes of digestion and absorption. Whydowehavetoknowthis?Doweneedtounderstandthebasicfactsabout how we obtain and process our nutrients in order to understand or remedy the consequences of malnutrition? The answer, of course, is yes. To give just one example, substantial percentages of certain adult populations are deficient in the enzyme lactase. Lactase is an essential enzyme needed to digest lactose, the sugar found in milk products. People with this deficiency experience severe abdominal pain and diarrhea when they ingest any substantial amounts of milk products. How foolish it would be then, with all the best of intentions, to provide a malnourished population with this lactase deficiency large amounts of nutrient-rich powdered milk and cheese to supplement their diets (yet this has indeed happened, or we would not be using it as an example). Anatomy Although the gastrointestinal tract is fundamentally one long tube, each of thesegmentsisperfectlyadaptedtoperformitsparticularfunction.1Thehuman gastrointestinal (hereafter gi) tract can also be viewed as the means by which we most intimately interact with our external environment, by internalizing external nutrients and incorporating “them” into “us.” As an analogy, our respiratory system is similar in this particular regard, albeit far less intricately incorporative, as it basically just exchanges the inorganic gases oxygen (which is, of course, incorporated into our tissues) and carbon dioxide and water vapor (which are waste products of our...

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