Hematopoietic stem cell niche
Many human blood cells, such as red blood cells (RBCs), immune cells, and even platelets all originate from the same progenitor cell, the hematopoietic stem cell (HSC). As these cells are short-lived, there needs to be a steady turnover of new blood cells and the maintenance of an HSC pool.
Source: Wikipedia — Hematopoietic stem cell niche (CC BY-SA 4.0)