How do bone marrow stem cells produce new blood cells?

In adults, the process of blood cell formation, or hematopoiesis, occurs continuously within the bone marrow. This process relies on primitive stem cells that possess the ability to develop into various blood cell precursors.1

These stem cells undergo a series of complex transformations, dividing and differentiating into committed precursor cells that eventually give rise to four major lineages: red blood cells, phagocytic cells, megakaryocytes (which form platelets), and lymphocytes.1

This development is regulated by colony-stimulating factors (CSFs), which are hormonal glycoproteins produced throughout the body. These factors act as signals that respond to the body's changing needs:1
* Multi-CSF (interleukin-3): Stimulates the most ancestral hematopoietic stem cell.1
* Erythropoietin: Specifically required for the maturation of red blood cells; its production increases when blood oxygen levels drop.1
* Granulocyte CSF: Controls the production of phagocytic granulocytes, which increases in response to infection.1

Once mature, these new blood cells enter the general circulation by penetrating the walls of the marrow's venous sacs, known as sinusoids.1