Bone, critical organ

Systemic poisons attack organs other than the site of contact. The critical organs arc the kidneys, liver, blood and bone marrow. 

O. 183 450, 0.148 500, 0.119 550, 0.096 600, 0.078. Special precautions Bone is the critical organ in terms of dose. The effective biological half-life in humans is nearly 20 years. Double gloving is recommended when working with this radionuclide. 

Special precautions The maximum range in air is 6 meters, and the maximum range in water is 8 mm. Because bone concentrates phosphate, is the critical organ in terms of dose. Store this radioisotope behind 1-3 cm Lucite shielding. Avoid working over open containers, and exercise institutional guidelines on the type and location of dosimeters. 

Quabeck K. The lung as a critical organ in marrow transplantation. Bone Marrow Transplant 1994 14 819-28. 

Maximum contaminant levels in community water systems — average annual concentrations assumed to produce a total body or organ dose of 4 millirem/year 9°Sr Critical organ 8 pCi/L bone marrow EPA 2001f 40CFR141.16... 

Some 20% is assumed to enter the blood compartment. The ICRP biokinetic model for radium has the same general structure as that for strontium and uranium (see Figure 26.2-2). Bone is the critical organ with a biological half-life for radium in the range of 20 years. Since the decay of radium leads to the noble gas radon with a physical half-life of 3.8 days, most of the radioactivity of the decay product escapes from the body before further decays occur. 

The danger from radioactive substances is mainly due to the detrimental effects of the emitted ionizing radiation however, there are also toxic effects at the level of biochemical reactions. The most iihportant effects of radioactive radiation from accumulated radionuclides are manifested at a much later date in the form of genetic consequences. There are also local effects, since the radionucfides are frequently accumulated in a certain critical organ ( °Sr in bones, Cs in muscles, etc.). Thus, the local radiation dose can exceed by a factor as high as 50 the mean whole-body dose. In many cases, tumour growth may be induced. 

For whole body radiation the most critical organs and tissues are the lens of the eye, the blood-forming organs (red bone marrow), and the gonads. Internal radiation sources may affect several vital organs. 

The biomechanical properties of bone critically depend on this hierarchical strnc-ture. The macro-scale organization of osteons and Haversian canals provides long bones with their characteristic mechanical anisotropy. The microscale porosity in bone is ideal for cell migration and vascularization, whereas the nano-scale featnres act as a cell and mineral binding architecture [5]. 

Some of the critical enzymes in our cells are metalloproteins, large organic molecules made up of folded polymerized chains of amino acids that also include at least one metal atom. These metalloproteins are intensely studied by biochemists, because they control life and protect against disease. They have also been used to trace evolutionary paths. The d-block metals catalyze redox reactions, form components of membrane, muscle, skin, and bone, catalyze acid-base reactions, control the flow of energy and oxygen, and carry out nitrogen fixation. 

B39. Bone, R. C., Balk, R. A., Cerra, F. B Dellinger, R. P Fein, A. M., Kanus, W. A., Schein, R. M. H., and Sibbald, W. J., American College of Chest Physicians/Society of Critical Care Medicine Concensus Conference Definitions for sepsis and organ failure and guidelines for the use of innovative therapies in sepsis. Crit. Care Med. 20-6, 864-873 (1992). 

It is the divalent metal cation Ca + that is absolutely critical in human physiology. It is important both structurally and functionally. I noted above that hydroxyapatite, a phosphate salt of calcium, is an integral component of bone. As a component of bone, calcium is quantitatively one of the most abundant elements in higher organisms, such as humans. 

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