The peripheral blood contains cellular components which circulate through the heart, arteries, capillaries, and veins.
This anatomical compartment includes the common lymphoid progenitor cells and common myeloid progenitor cells, as well as their descendants, not necessarily because they are commonly present in the blood circulation, but since they are located in many anatomical locations related to the blood (i.e. AGM, Bone Marrow, etc.) and were included in this compartment for the sake of simplicity.