| Term | Definition |
| B lymphocytes | A type of lymphoid cell that matures in bone marrow and produces antibodies as part of adaptive immunity. |
| Differentiation | The process by which unspecialized stem cells develop into specific types of blood cells with distinct functions. |
| Erythropoietin (EPO) | A hormone (mainly from the kidneys) that stimulates red blood cell production in the bone marrow. |
| Hematocrit | The percentage of blood volume made up of red blood cells; used to assess oxygen-carrying capacity. |
| Hematopoietic stem cells | Pluripotent stem cells in bone marrow that can give rise to all types of blood cells. |
| Lymphoid lineage | A branch of hematopoiesis that produces lymphocytes (B cells, T cells, and NK cells). |
| Myeloid lineage | A branch of hematopoiesis that produces erythrocytes, platelets, and most white blood cells (except lymphocytes). |
| Polycythemia | A condition characterized by an abnormally high number of red blood cells, increasing blood viscosity. |
| Red bone marrow | The active tissue where hematopoiesis occurs and blood cells are produced. |
| T lymphocytes | A type of lymphoid cell that matures in the thymus and is involved in cell-mediated immunity. |
| Yellow bone marrow | Bone marrow primarily composed of fat; can convert to red marrow under certain conditions (e.g., severe blood loss). |