22.6 : Production of Formed Elements

Hemangioblasts, the multipotent stem cells of mesodermal origin, give rise to hematopoietic stem cells or HSCs.

The HSCs undergo hematopoiesis to produce all formed elements of blood.

Hematopoiesis is tightly regulated by a network of hematopoietic growth factors, including transcription factors, growth factors, and cytokines, that stimulate the HSCs to divide and differentiate.

However, a small fraction of HSCs remain undifferentiated to establish a self-renewing HSC pool.

Most HSCs commit to the myeloid or lymphoid lineage during development by expressing lineage-specific cell receptors and signaling molecules.

Once committed to a specific lineage, the common myeloid progenitors, or CMP, and common lymphoid progenitors, or CLP, undergo lineage-specific differentiation.

The CMPs can further differentiate into more specialized cells like the granulocyte-macrophage, megakaryocyte, erythrocyte, and mast progenitors.

These specialized progenitors then give rise to specific cells, such as neutrophils, monocytes, eosinophils, basophils, macrophages, platelets, erythrocytes, and mast cells.

In contrast, the CLPs give rise to all lymphoid cells, including B, T, and natural killer cells.