Stroma
The stroma of the bone marrow is all tissue not directly involved in the primary function of hematopoiesis. Yellow bone marrow makes up the majority of bone marrow stroma, in addition to smaller concentrations of stromal cells located in the red bone marrow. Though not as active as parenchymal red marrow, stroma is indirectly involved in hematopoiesis, since it provides the hematopoietic microenvironment that facilitates hematopoiesis by the parenchymal cells. For instance, they generate colony stimulating factors, which have a significant effect on hematopoiesis. Cells that constitute the bone marrow stroma are:
- fibroblasts (reticular connective tissue)
- macrophages
- adipocytes
- osteoblasts
- osteoclasts
- endothelial cells, which form the sinusoids. These derive from endothelial stem cells, which are also present in the bone marrow.
Macrophages contribute especially to red blood cell production, as they deliver iron for hemoglobin production.
Read more about this topic: Bone Marrow