In an adult, most RBCs, WBCs, and platelets originate in the bone marrow. Hematopoietic pluripotent stem cells are the earliest precursor cell and they are created in the bone marrow. These stem cells can self renew or differentiate into myeloid progenitor or lymphoid progenitor cells.

Myeloid progenitor cells can differentiate into granulocytes, monocytes, erythrocytes (RBCs), and platelets.

Lymphoid cells can differentiate into T-cells and B-cells.

Let’s dive into myeloid cells first and then we’ll circle back to lymphoid cells.  Myeloid progenitor cells can become 6 different cell types: neutrophils, basophils, eosinophils, monocytes, erythrocytes, and platelets. Neutrophils, basophils, and eosinophils (collectively granulocytes) follow the same maturation pattern within their cell type.

RBCs will follow this same pattern but instead of using myelo-, RBCs will use rubri-.

Your natural intuition might guide you to think metamyelocyte comes before myelocyte but this is not true, in fact in Greek the word meta means “after.” So the most important sequence to remember is:

Monocytes and platelet development is categorized slightly differently and looks like this:

Lymphoid progenitor cells can differentiate into T-cells and B-cells. They are called T or B cells because of where they differentiate. T-cells in the thymus, and B-cells in the bone marrow. Lymphoid progenitor cells can also differentiate into Natural Killer (NK) cells. Lymphocyte development is categorized as follows: