Hematopoiesis is the process of formation of blood cells. It may be also called hemopoiesis, hematogenesis, or hemogenesis. The cells from which the blood cells are formed are called hematopoietic stem cells (HSC). Hematopoiesis is initiated from similar type of cells, but differentiates into various types. Thus, hematopoietic stem cells are multipotent or pluripotent in nature.
Primarily, hematopoiesis occurs within the medulla of bone marrow (usually long bones in children, vertebrae, pelvic bones, sternum, and cranium in adults. Hematopoiesis is initiated with the differentiation of multipotent stem cells as follows:
1) Multipotent stem cells or hemocytoblasts, differentiates into:
(a) common lymphoid progenitor cell (b) common myeloid progenitor cells.
2) Common lymphoid progenitor cells generate primary lymphoid cells, lymphoblast, the primary lymphocytes, which matures into lymphocytes as,
(a) B-lymphocytes (designated from Bursa of Fabricus in birds, which matures within bone marrow itself), which further produces the plasma cells,
(b) T-lymphocytes (generated in the bone marrow, but mature in thymus),
(c) Natural killer cells (NK) and, also some dendritic cells.
3) Common myeloid progenitor cells give rise to progenitors of red blood cells and some white blood cells, as:
(a) Erythrocytes or red blood cells,
(b) Mast cells,
(c) Megakaryocytes, which forms the platelets,
(d)Myeloblasts, which further differentiates into promyelocyte, myelocyte, metamyelocyte precursors of the granulocytes, producing neutrophils, basophils and eosinophils.
Myeloblasts, also produce monocytes, which further differentiate to produce macrophages and myeloid dendritic cells.
Describe the different types of lymphoid cells that are found in the bone marrow, thymus and...