Hematopoietic stem cells or HSCs are multipotent, meaning they can form all types of blood cells. In an embryo, hematopoiesis occurs in the liver, where an HSC divides symmetrically, producing two daughter cells. These HSCs continue to multiply by self-renewal. Under the influence of growth factors called cytokines, the HSCs differentiate into progenitors of blood cells. In adults, HSCs reside in the bone marrow and interact with the surrounding stromal cells . Receptor-ligand interaction brings the HSC and the stromal cells together. Such cell-cell contact inhibits HSC proliferation as they enter the G0 state of the cell cycle and become non-dividing or quiescent. Upon tissue injury, vascular endothelium releases growth factors that allow the quiescent HSCs to lose contact with the surrounding stroma and migrate to the blood vessels. HSCs now undergo asymmetric division, maintaining the HSC pool and forming committed progenitors that differentiate into mature blood cells.