ABSTRACT
The body originates from a single fertilized ovum, which generates all body tissues including germ cells in the gonads; these contribute to a fertilized ovum ensuring continued propagation of the species. The generation of hydrogen peroxide as a function of body mass is inversely proportional to life expectancy, suggesting that oxygen free radical generation may be a major determinant in acquiring wear-and-tear injury. Central to understanding many diseases is the appreciation that an oxygen-rich environment is potentially toxic and that protection against oxidant-induced stress is key to cell survival. Genetic abnormalities resulting in abnormal proteins are implicated in many diseases. Stem cells found in bone marrow and umbilical blood can generate, for example, hepatocytes, neurons, or cardiomyocytes; these may be useful in treating specific diseases or used as part of gene replacement therapy. Genetic disease, both chromosomal abnormalities and single gene defects, can cause physical and mental impairments.
