Adult human skeleton

Durbin PW, Schmidt CT, Mclnroy JF, et al. 1985. Estimation of initial distribution of americium in adult male human skeleton. Health Phys 49(1) 162. 

Calcitonin is a polypeptide hormone that (along with PTH and the vitamin D derivative, 1,25-dihydroxycholecalciferol) plays a central role in regulating serum ionized calcium (Ca2+) and inorganic phosphate (Pi) levels. The adult human body contains up to 2 kg of calcium, of which 98 per cent is present in the skeleton (i.e. bone). Up to 85 per cent of the 1 kg of phosphorus present in the body is also found in the skeleton (the so-called mineral fraction of bone is largely composed of Ca3(P04)2, which acts as a body reservoir for both calcium and phosphorus). Calcium concentrations in human serum approximate to 0.1 mg ml-1 and are regulated very tightly (serum phosphate levels are more variable). 

In addition to the modern faunal samples, the second author collected eleven samples from archaeological human skeletons at Conchopata. Six of these individuals were buried in two tombs at Conchopata. Tooth enamel and bone samples were collected from five adults interred in an undisturbed tomb in Architectural Space 105 (EA 105), and an infant from a looted tomb in Architectural Space 06 (EA 06). 

For adult humans, the typical body contains 1,200 grams of calcium, 99 percent of which is found in the skeleton. The remaining calcium, which is contained in the blood and soft tissue, performs fovu metaboHc functions It regulates cellular activity, including cell division, adhesion, and apoptosis (programmed cell death) it helps muscles contract and is critical to the transmission of nerve impulses in the bloodstream, it neutralizes excess acidity and facilitates coagulation and, finally, it triggers the secretion of hormones." ... 

Calcium is the fifth most abundant element on earth and the principal extracellular divalent cation in the human body. A healthy, 70-kg adult contains 1-1.25 kg of calcium (25-33 g/kg of fat-free tissue), while a 3.5-kg newborn contains about 25 g of calcium. About 95-99% of body calcium is in the skeleton as hydroxyapatite crystals. The remainder is in the extracellular fluid and is exchangeable with that in periosteal fluid, bone-forming surfaces, and soft tissues. Skeletal calcium is slowly exchangeable with extracellular fluid calcium, and the skeleton is thus a reservoir of calcium. The steady-state extracellular and periosteal fluid concentrations of calcium depend, in large part, on the balance between bone formation and bone resorption, which are regulated by hormones. 

The distribution of absorbed strontium in the human body is similar to that of calcium, with approximately 99% of the total body burden in the skeleton (ICRP 1993). The strontium skeletal burden has been estimated from analyses of bone samples from human autopsies (Herring and Keefer 1971a O Connor et al. 1980 Papworth and Vennart 1984 Tanaka et al. 1981). Skeletal burden was estimated in Japanese adult males to be approximately 440 mg compared to 850 g of calcium (Tanaka et al. 1981). 

Experiments carried out on laboratory animals have shown that (radioactive) strontium is rapidly deposited in the skeleton, from which it is only slowly removed in the normal process of metabolism. Once ingested, of the total amount in vertebrate animals or humans more than 99 % of the strontium is localized in bone and connective tissue, which in total is about 320 mg for a 70-kg adult. For herbivorous animals the bone strontium level is higher than that present in humans, probably due to the higher dietary intake of strontium from plant material. Retention of strontium in the human body after oral doses of 100-250 mg has amounted to 12-24% in a month (Harrison et al. 1955). More strontium is absorbed by persons on a low calcium intake than on a high calcium intake. Animal as well as human studies have demonstrated that the intestinal absorptions of strontium and calcium are comparable, which led to the hypothesis that these elements share a common carrier system in the intestinal wall (Reid etal. 1986). Stron-... 

The barium content of human tissues is dependent on age. For example, in adults the liver contained barium levels of 4-20 mg kg dry matter, whereas in children the typical liver barium content was much higher, at 144 mg kg The majority of tissue barium is accumulated in the skeleton, with typical adult levels ranging from 16 to 95 mg kg dry matter. Very high barium contents were also determined in the prostate gland of children, with up to 1.3gkg dry matter in infants (Jaritz 1998). Other sources have described lower levels of barium in human tissues however... 

Nine amino acids are essential in the human. Essential means that the carbon skeleton cannot be synthesized and, therefore, these amino acids are required in the diet (Table 3). The essential amino acids are also called the indispensable amino acids. Arginine is essential during periods of growth in adults it is no longer considered essential. 

Elements like aluminium, barium, cadmium, lead, strontium, and traces of others exist in different forms in plastics additives, and may enter the body through food and water as well as through air breathed in. These elements do not serve any known purpose in the body, but they are still absorbed, and as a result, the average adult body can contain significant amounts of them. Some of these resemble human elements (e.g., strontium resembles calcium closely, and a lot of it is absorbed easily in bones, to the extent that approximately 320 mg can be found in the body of an average person, which is far more than many of the essential elements, while even gold and uranium can exist in quantities of 7 and 0.07 mg, respectively), and are retained and deposited preferentially either in the skeleton (e.g., uranium, binds specifically to the phosphate of the bones) or elsewhere for example in the liver, where liver proteins can trap and deposit some of these heavy metals, like cadmium. 

The whole-body content of Co in an adult of 70 kg is estimated to be 1.1 mg, 85% of which is incoq)orated into cobalamines or linked with low molecular weight proteins [14]. The remaining 15% is in the skeleton. The total amount of vitamin B12 in the body is 2-5 mg (i.e., 0.09-0.22 mg of Co the vitamin containing 4.34% of Co) [18,21]. In humans and animals, Co does not accumulate in a target organ. Nevertheless in humans the highest levels are found in liver and kidney [17]. 

In addition to their compositional similarity to human bones, dog bones are accessible to biopsy for longitudinal study of nutritional effects on the skeleton. This property, plus their rapid rate of remodelling, suggests that adult dogs are capable of yielding nutritional information relevant to human osteoporosis within a practicable experimental time frame. 

The content of magnesium in the body of an adult is about 25-40 g. This accounts for about 60% of the content of the skeleton. The highest concentrations of magnesium in soft tissues are found in the pancreas, liver and skeletal muscles. Blood and extracellular fluids contain only 1% of the total amount of magnesium in the body. Calcium is quantitatively the major mineral component in the human body. The total amount is about 1500g, with 99% of this being in bones and teeth as calcium phosphate. 

In an adequately supplied adult male human subject, the total body selenium content is on the order of 30-60 mg, of which one-third is found in the skeleton and two-thirds in the soft tissues. A substantial fraction of kidney selenium is retained even when selenium at other sites is severely depleted during deficiency, and renal selenium is more constant between human populations than selenium in other tissues or body fluids. Regulation of selenoprotein synthesis at the transcription level appears to ensure a hierarchy of preservation of individual selenoproteins at critical sites. The cytosolic glutathione peroxidase (GPx I) and selenoprotein P can donate selenium to other sites whenever overall depletion occurs. Selenium crosses the placenta readily, and breast milk selenium concentration is responsive to changes in maternal selenium intake. In the United States, breast milk Se concentrations are generally in the range of 0.19-0.25 pmol/1, but colostrum has levels that are two or three times higher than those of mature breast milk. 

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