|MadSci Network: Biochemistry|
Dear Paul, This question is very interesting. We must look to the physiology and cellular anatomy of the various tissues of the human body to begin to answer it. Some cells are replaced very rapidly. The cells lining the small intestine are most rapidly replaced and all may be new in just a few days. Other cells, such as the nerves, brain, and spinal cord, are so specialized that they have lost the ability to replace themselves and are never replaced, even if they are damaged. This has some good points because if you replace brain or nerve cells, you would lose memory and reflex arcs. Bone is made up of organic cells and of inorganic calcium hydroxy apatite crystals. Bone is one of the more slowly replaced tissues of the body, but it is replaced. It may take up to seven years for all of the material in your bones to be dissolved and rebuilt. Remember, you cannot replace atoms in a cell without having some effect on the DNA, membranes and organelles that make up the cell. Other atoms are used as food or as the oxidizer to burn the food. These atoms may be recycled very rapidly. Atoms that are part of the strucutre of long-lived cells may reside in your body for your entire lifetime. Baby girls are born with all of the egg cells they will ever have (about 2 million). Not only that, but these eggs are arresed in their development and do mature only one at a time after the onset of puberty. The atoms of these eggs are the same ones the girl/woman was born with and will be the same ones she dies with (Except for the five-hundred or so she shed through ovulation during her lifetime.) When cells are replaced, the daughter cells are made up of the nutrients in the blood. The atoms of these nutrients may have come from digested food that has been in your body less than 24 hours, or from other tissues in your body that are being recycled. The iron in your hemoglobin, for example, is captured by your liver after the red blood cells break from being folded inside the very small capillaries in the spleen. Men normally have a several-year supply of iron in their bodies because they normally do not lose much blood and because of this recycling process even though RBC's only live for about 120 days! These iron atoms may have been in your body for years! An answer to your question is very complex. There are on the order of 100 Trillion cells in your body and each is made up of hundreds of trillions of atoms. To trace each one in light of the complexities of new and recycled tissues, would require more than a simple answer that could be posted on this site. I would direct you to a good histology book. Histology is the study of tissues on the cellular level and such a medical textbook goes into great detail about the interactions of these cells. May I recommend: Histology, by Arthur W. Ham. The Latest Edition (mine is the 7th,1974). I do not know of a comparable text in Romanian and material of this level of detail is best understood in a person's native language. You may not have access to such books in Romania. If you need more information or would like to discuss this further, please contact me at LONBROUSE@AOL.COM. I hope this helps.
Try the links in the MadSci Library for more information on Biochemistry.