22.6: Production of Formed Elements
Hemangioblasts are multipotent stem cells originating from the mesoderm. They give rise to hematopoietic stem cells (HSCs), which undergo hematopoiesis to produce all the formed elements of blood. This process is regulated by a complex network of hematopoietic growth factors, including transcription factors, growth factors, and cytokines. These factors stimulate the HSCs to divide and differentiate, though some HSCs remain undifferentiated to maintain a self-renewing pool.
Most HSCs commit to either the myeloid or lymphoid lineage during development by expressing specific cell receptors and signaling molecules. Once committed to a lineage, the common myeloid progenitors (CMP) and common lymphoid progenitors (CLP) undergo further differentiation specific to their lineage. The CMPs can differentiate into more specialized cells such as granulocyte-macrophage, megakaryocyte, erythrocyte, and mast progenitors. These progenitors then produce specific cells, including neutrophils, monocytes, eosinophils, basophils, macrophages, platelets, erythrocytes, and mast cells. Conversely, the CLPs give rise to all lymphoid cells, such as B cells, T cells, and natural killer cells.
