Overview of Hematopoiesis

Hematopoiesis, or hemopoiesis, is the production of the formed elements in blood from common progenitors, called hematopoietic stem cells, or HSCs.

During development, HSCs originate in the embryonic yolk sac and migrate to the fetal liver, spleen, thymus, and lymph nodes for hematopoiesis.

In newborns and children, hematopoiesis gradually shifts to the red bone marrow, a soft reticular connective tissue found in all skeletal bones.

Under the influence of growth factors and cellular signals, the HSCs transform into specific types of blood cells.

For instance, an infection upregulates differentiation into white blood cells, while blood loss increases the production of red blood cells and platelets.

As a result, the red marrow comprises a rich network of different types of HSC-derived blood cells and their progenitors at various stages of development.

As children age, the red bone marrow in the long bones is gradually replaced by the yellow bone marrow, which is rich in fat cells.

Due to this, adult hematopoiesis is restricted to bones, such as the vertebrae, sternum, ribs, the proximal epiphysis of the femur, and humerus.