Erythropoietin (EPO) is the hormone involved in the stimulation of red blood cell production. The cells that produce erythropoietin are sensitive to the low oxygen levels in the blood, and they release erythropoietin into the blood at low oxygen concentrations. The main function of erythropoietin is to promote the differentiation and development of red blood cells. It also initiates the production of hemoglobin. Therefore, erythropoietin stimulates the production of red blood cells in the bone marrow.
Key Areas Covered
1. How is Red Blood Cell Produced
– Definition, Facts, Stages
2. What Hormone Stimulates Red Blood Cell Production
– Stimulation of Red Blood Cell Production by Erythropoiesis
Key Terms: Bone Marrow, Erythropoietin (EPO), Hemoglobin, Peritubular Cells, Red Blood Cells
How is Red Blood Cell Produced
The process of red blood cell production is called the erythropoiesis. It occurs in the bone marrow of adults. During fetal development, it occurs in the yolk sac. It occurs in the liver at the third trimester of fetal development. Hematopoietic stem cells or hemocytoblasts in the bone marrow are responsible for differentiating into red blood cells. Immature reticulocytes are released into the bloodstream for further maturation. The whole process takes about 5 days to complete. The production of red blood cells from hemocytoblast is shown in figure 1.
Figure 1: Red Blood Cell Production
Red blood cells or erythrocytes are enucleated biconcave cells. Approximately, 4-6 million of red blood cells can be found per microliter of blood. They remain in the bloodstream for about 120 days. The main function of red blood cells is to transport oxygen throughout the body. Hemoglobin is the pigment in red blood cells that binds to oxygen. One-third of the volume of the red blood cell is occupied by hemoglobin.
What Hormone Stimulates Red Blood Cell Production
Erythropoietin is the hormone that is responsible for the stimulation of the production of red blood cells. It is mainly produced by the peritubular cells in the kidney. The kidney cells that produce erythropoietin are sensitive to oxygen levels in the blood. When the oxygen level in the blood is low, a transcription factor known as ‘hypoxia-induced factor’ moves into the nucleus of peritubular cells and induces the transcription of erythropoietin gene. Consequently, the kidney releases erythropoietin into the blood at low concentrations of oxygen. Some erythropoietin is produced in the liver as well. Erythropoietin stimulates the differentiation and development of hematopoietic stem cells into red blood cells in the bone marrow. It also increases the production of hemoglobin, which in turn, increases the carrying capacity of oxygen in the blood. The stimulation of red blood cell production by erythropoiesis is shown in figure 2.
Figure 2: Stimulation of Red Blood Cell Production
Normal levels of erythropoietin in the blood should be 0-19 mU/mL. Altered levels of erythropoietin in the blood indicate disorders in bone marrow or kidney disease.
Conclusion
The production of red blood cells is stimulated by a hormone called erythropoietin, which is mainly produced by the kidney. The peritubular cells in the kidney are sensitive to the oxygen levels in the blood, and they release erythropoietin when the level of oxygen in the blood is low. Erythropoietin stimulates the differentiation and development of red blood cells in the bone marrow. This increases the oxygen levels in the blood.
Reference:
“Definition of Hormone, Erythropoietin.” MedicineNet, Available here.
Image Courtesy:
1. “Illu blood cell lineage” (Public Domain) via Commons Wikimedia
2. “EPO Hämatopoese” By Jamiri at the German language Wikipedia (CC BY-SA 3.0) via Commons Wikimedia
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