Physiological Role Tissue Concentrations

The average human body contains between 200 and 400 mmol of manganese, which is fairly uniform in distribution throughout the body. There is relatively little variation among species with regard to tissue manganese concentrations. Manganese tends to be highest in tissues rich in mitochondria; its concentration in mitochondria is higher than in cytoplasm or other cell organelles. Hair can accumulate high concentrations of manganese, and it has been suggested that hair manganese concentrations may reflect manganese status. High concentrations of manganese are normally found in pigmented structures, such as retina, dark skin, and melanin granules. Bone, liver, pancreas, and kidney tend to have higher concentrations of manganese (20-50 nmolg-1) than do other tissues. Concentrations of manganese in brain, heart, lung, and muscle are typically <20nmolg~1; blood and serum concentrations are approximately 200 and 20nmoll~1, respectively. Typical concentrations in cow milk are on the order of 800 nmol l-1, whereas human milk contains 80 nmol l-1. Bone can account for up to 25% of total body manganese because of its mass. Bone manganese concentrations can be raised or lowered by substantially varying dietary manganese intake over long periods of time, but bone manganese is not thought to be a readily mobilizable pool. The fetus does not accumulate liver manganese before birth, and fetal concentrations are significantly less than adult concentrations. This lack of fetal storage can be attributed to the apparent lack of storage proteins and the low prenatal expression of most manganese enzymes.

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