A schematic representation of the control of HSC regeneration. Proliferating phase cells include those cells in G₁, S (DNA synthesis), G₂, and M (mitosis), whereas the resting phase cells are in the G₀ phase. Local regulatory influences are exerted via a cell number dependent variation in the rate of entry into proliferation. Differentiation into all of the comitted stem cell populations occurs from the G₀population, whereas there is a loss of proliferating phase cells due to apoptosis. See Mackey191 and Milton and Mackey192 for further details.