The study of trace element dynamics provides insight into the significance of various body pools of elements as well as the regulation of their routes of absorption and excretion. It is apparent that the large pools of an element, often in muscle, bone or liver, play an important role in homeo- stasis and whole-body metabolism.
However, except for Zn and Fe, the meta- bolism of the major body pools of trace elements has received little attention. Large pools may serve as a source or sink during periods of dietary insufficiency or excess.
On the other hand, as in the case of muscle Zn in rats, the body attempts to maintain a constant concentration of the element at the expense of other pools during periods of deficiency. Compartmental modelling is an effective tool for compiling information on trace element dynamics. It also serves as a planning assistant in the design of studies and greatly facilitates understanding the
complexities of whole-body metabolism. A fairly complete picture of the dynamics of Zn metabolism in young rats receiving deficient to adequate diets is now available, although the upper ranges of the homeo- static plateau for individual tissues and the whole animal have not been well estab- lished. Much work yet needs to be done on Cu, Mn and Se, particularly with respect to the regulation of body compartments and, especially for Se, the roles of absorption and endogenous excretion in homeostasis. The effects of various physiological states, other than growth, on trace element dynamics were not addressed in this chapter;
however, research on the affects of ageing, gestation and lactation shows that these are productive areas of research in trace element dynamics. For all the elements discussed in this chapter, the quantity of research conducted in dynamics with rats and humans exceeds that performed with farm animals, but an effort was made to include farm animal results as much as possible. Until a greater body of knowledge is accumulated, extrapolation of the prin- ciples to farm animals will be necessary, although caution is required because of substantial differences in the metabolism of some elements among species.
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