Abstract
This chapter highlights cell renewal. It presents investigations on mitotic rates and renewal times of the major organs in the rat. Many organs, throughout life, undergo renewal of their constituent cells. Cell renewal is the basis of exfoliative cytology and thus of the cytodiagnosis of cancer. Cells are continuously desquamated and extruded, and the lost cells are replaced by new ones arising by mitosis. The time required for total renewal of all cells of a tissue or organ can be determined by mitotic count. The rate of cell production in organs can be determined by several methods. When a cell population is destroyed, the time required for regeneration can be observed. Another direct approach to estimate mitotic rates is to ascertain the percentage of dividing cells in tissues. This is achieved by enumerating resting and dividing nuclei in histological sections. This method is mainly applied when relative values of mitotic activity are sufficient—such as when comparing the effects of various agents on the mitotic rates of the epidermis. Various factors influence the mitotic rate: (1) alimentation and nutrition, (2) diurnal variation, and (3) endocrine control of mitotic activity.
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