Minerals body compartments

Measurements of True Magnesium Absorption. Appearance of a single ingested isotope in the plasma or urine can not provide a quantitative estimate of fractional absorption of a mineral without concomitant measurement of Isotope exchange between the mineral in the plasma and other body compartments 2A). Table IV shows the levels of urinary Mg from an intravenous injection that accompanied an oral dose of 50 mg Mg. Radioactivity was determined in 15 ml urine with a relative S.D. of < 1% in composites collected at Intervals up to 24 hours, and with < 4% in the 24-48 h collection. The relative standard deviations for Mg measurements were consistently higher, reaching unacceptable levels in samples taken after 12 hours following the test meal. 

Regulation of Calcium Homeostasis Calcium homeostasis necessitates the maintenance of a dynamic equilibrium of calcium fluxes between three different compartments which harbor the mineral ion in vastly different concentrations. Thus, homeostatic control mechanisms ought to modulate calcium fluxes between different body compartments in a way which allows the generation and maintenance of steep concentration gradients between the skeletal tissue, the extracellular fluid and the intracellular - that is, the cytoplasmic compartment. Of particular importance thereby is the rigid control of plasma free Ca " ", because even small deviations from the normal level induce profound changes in both intracellular free Ca, as well as in the amount of calcium deposited at skeletal sites, inevitably causing adverse effects on bone health (cf. Whedon 1980). 

The minerals are held in different forms in the body, which can be considered as compartments. There is a central reserve or interchange compartment, which is usually blood plasma, and one or more compartments that interchange the mineral with the central compartment at various rates, e.g. compartments easy or difficult to mobilise. Metabolic processes take place via the central reserve (plasma), which receives minerals from other compartments, the digestive tract and the difficult to mobilise compartment. The central reserve secretes mineral into the readily mobilised compartments, the difficult to mobilise compartment, the gastrointestinal tract, the kidneys and milk. The flux between the compartments can be measured by a combination of balance trials and injection of radioactive marker followed by sampling the tissues over time. An example of the body compartments of copper is shown in Fig. 6.1. 

This compartment contains about one-third of total body water and is distributed between the plasma and interstitial compartments. The extracellular fluid is a delivery system. It brings to the cells nutrients (eg, glucose, fatty acids, amino acids), oxygen, various ions and trace minerals, and a variety of regulatory molecules (hormones) that coordinate the functions of widely separated cells. Extracellular fluid removes COj, waste... 

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