The architecture and control of hematopoiesis. This figure gives a schematic representation of the architecture and control of platelet (P), red blood cell (RBC), and monocyte (M) and granulocyte (G) (including neutrophil, basophil, and eosinophil) production. Various presumptive control loops mediated by TPO, EPO, and G-CSF are indicated, as well as a local regulatory (LR) loop within the totipotent HSC population. CFU (BFU) refers to the various colony (burst) forming units (Meg, megakaryocyte; Mix, mixed; E, erythroid; G/M, granulocyte/monocyte) that are the in vitro analogs of the in vivo committed stem cells (CSC).