[The nature and biological role of near-weekly rhythm]

Main peculiarities and possible mechanisms of the rhythms of proliferative activity and other characteristics of the tissue with near-weekly period are discussed. It is suggested that these variations may be explained by means of a simplest model which involves only processes of cell division and death with a delay of division stimulus about 24 hours, which corresponds to the duration of the mitotic cycle. In such a model there are periodic variations of the cell number with the period 4-7 times greater than the delay time.