Hematopoiesis is a complex biological process that leads to the production
and regulation of blood cells. It is based upon differentiation of stem cells
under the action of growth factors. A mathematical approach of this process is
proposed to carry out explanation on some blood diseases, characterized by
oscillations in circulating blood cells. A system of three differential
equations with delay, corresponding to the cell cycle duration, is analyzed.
The existence of a Hopf bifurcation for a positive steady-state is obtained
through the study of an exponential polynomial characteristic equation with
delay-dependent coefficients. Numerical simulations show that long period
oscillations can be obtained in this model, corresponding to a destabilization
of the feedback regulation between blood cells and growth factors. This
stresses the localization of periodic hematological diseases in the feedback
loop