Skeletal pool functions

The lead content in the skeleton in occupationally unexposed subjects varies in different geographical areas of the world. It is around a few milligrams in prehistoric subjects, living in a world with no traffic or industries (Ericson etal. 1979), about 10 mg in temporary Scandinavians (Schiitz et al. 1987a), and about 100 mg in subjects from the UK (Barry 1975) and the US (Ericson et al. 1979). In long-term and heavily exposed lead smelter workers, the skeletal lead content may be in the order of 1 g. There is a continuous turn-over of the skeletal bone, and in long-term-exposed subjects, the skeletal pool functions as an endogenous source of lead. 

Compounds isolated from natural sources are frequently optically pure. Thus camphor (11), cholesterol (14), morphine (16), for example, are isolated in the optically pure state. The parent molecule of (13) is D-glucose, and like camphor and cholesterol is readily available in very large quantities. These, and comparable compounds, form what is now described as a chiral pool, i.e. low-cost, readily available, chiral compounds which provide starting materials for conversion into other compounds, of simplified skeletal and functional structure, in which some or all of the chiral features have been retained. 

Fig. 42.3. Interorgan amino acid exchange after an overnight fast. After an overnight fast (the postabsorptive state), the utilization of amino acids for protein synthesis, for fuels, and for the synthesis of essential functional compounds continues. The free amino acid pool is supported largely by net degradation of skeletal muscle protein. Glutamine and alanine serve as amino group carriers from skeletal muscle to other tissues. Glutamine brings NH4 to the kidney for the excretion of protons and serves as a fuel for the kidney, gut, and cells of the immune system. Alanine transfers amino groups from skeletal muscle, the kidney, and the gut to the liver, where they are converted to urea for excretion. The brain continues to use amino acids for neurotransmitter synthesis.

Even for simple molecules, there will be many vibrational signals. A simple molecule can generate a complex spectrum. In a polymer, the repeating unit represents the simple molecule that will be generating a pool of signals or bands. Bands of vibrations associated with the presence of characteristic functional groups are called skeletal vibrations, and these skeletal vibrations are likely to constitute a pattern or fingerprint of the molecule as a whole. 

The human body has the capacity to store carbohydrate in the form of muscle and liver glycogen, and to store fat as triglycerides in adipose and muscle tissue. However, there is no comparable storage pool for protein. Yet, under conditions of energy or protein deficit, proteins that serve a variety of functions must be catabolized. When needed, the body can utihze skeletal muscle protein as a somewhat dispensable protein and energy reserve. With an inadequate supply of protein, AAs can be mobifized from muscle protein catabolism and used to synthesize proteins more essential to survival than skeletal muscle. Similarly, with an inadequate supply of carbohydrate, AAs from protein catabohsm are used as substrate for gluconeogenesis to maintain an adequate supply of blood glucose. 

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