Erythropoiesis

Erythropoiesis is the process by which red blood cells or erythrocytes are generated in the bone marrow.

Erythrocytes contain hemoglobin that binds oxygen and delivers it to the tissues.

An injury followed by blood loss reduces the number of erythrocytes in the body, decreasing the oxygen reaching the tissues. 

Low oxygen levels prevent the degradation of the transcription factor HIF-1ɑ. Accumulating HIF-1ɑ transcribes the erythropoietin or Epo gene, releasing more Epo into the blood.

Increased Epo levels stimulate erythroid progenitor cells in the bone marrow to proliferate and differentiate into colony-forming unit-erythroid or CFU-E.

As CFU-Es continue to divide and mature, they accumulate hemoglobin, lose their nucleus, and develop into immature reticulocytes.

Reticulocytes leave the bone marrow and move into the bloodstream, where they lose their ribosomes, mitochondria, and other organelles and undergo extensive membrane remodeling to form mature erythrocytes.