Fig. 1.

Unit Response, UR(t) (Eq. 1, Eq. 14), characterizing the disposition function of a hematopoietic cell. The cell is present in the systemic circulation when UR(t) = 1. Thus, ‘a’ and ‘b’ represent the disposition function parameters for the appearance and disappearance of the cell from the systemic circulation, respectively, and ‘s’ is the time of erythroid progenitor cell stimulation. Time variance of the ‘UR’ is considered (lower panel B) by assuming the ‘a’ value to be variable and determined at the time (t = s) of the progenitor cell stimulation