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aging (a´jing)

1. The process of growing old, especially by failure of replacement of cells in sufficient number to maintain full functional capacity; particularly affects cells (e.g., neurons) incapable of mitotic division. 2. The gradual deterioration of a mature organism resulting from time-dependent, irreversible changes in structure that are intrinsic to the particular species, and that eventually lead to decreased ability to cope with the stresses of the environment, thereby increasing the probability of death. 3. In the cardiovascular system, the progressive replacement of functional cell types by fibrous connective tissue. 4. A demographic term, meaning an increase over time in the proportion of older persons in the population.
clonal a. the deterioration in successive generations of a clone; thus paramecia and other simple forms, if allowed to reproduce asexually for a number of generations, invariably undergo deterioration, the characters of each group of descendants progressively departing from those of the original sexually produced ancestor.


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