Main Difference – Hematopoiesis vs Erythropoiesis
Hematopoiesis and erythropoiesis are two processes involved in the formation of mature blood cells. All blood cells are generated from the progenitor cell called Hematopoietic Stem Cell (HSC). The process of division and differentiation of HSCs is highly regulated. Hematopoiesis begins during the fetal life in the yolk sac and later, in the liver and spleen. After birth, it occurs in bone marrow. Hematopoiesis is completed through five processes: erythropoiesis, lymphopoiesis, granulopoiesis, monopoiesis and thrombopoiesis. The main difference between hematopoiesis and erythropoiesis is that hematopoiesis is the formation of mature blood cells whereas erythropoiesis is the formation of mature erythrocytes.
This article looks at,
1. What is Hematopoiesis
– Definition, Process, Function
2. What is Erythropoiesis
– Definition, Process, Function
3. What is the difference between Hematopoiesis and Erythropoiesis
What is Hematopoiesis
Hematopoiesis is the formation of mature blood cells. It is an active process throughout the lifetime of animals. Several types of blood cells are found in the circulation: red blood cells, white blood cells, and platelets. All types of blood cells are formed from a common progenitor called hematopoietic stem cells. The HSC is capable of self-renewing as well as differentiating into several types of blood cells. The derivation of blood cells occurs starting from HSC in the form of trunks of a tree. Each trunk describes the differentiation of each cell types from the progenitor cell. As the differentiation continues, the cells lose their capacity to differentiate into other cell types found in the other pathways. Five pathways are found in the differentiation tree which describes the hematopoiesis. They are erythropoiesis, lymphopoiesis, granulopoiesis, monopoiesis, and thrombopoiesis. Two major progenitor pathways are first derived from HSC: common myeloid progenitor and common lymphoid progenitor. Three types of blasts are first differentiated from common myeloid progenitor: megakaryoblast, proerythroblast, and myeloblast. Lymphoblast is differentiated from the common lymphoid progenitor. Hematopoiesis is shown in figure 1.
Figure 1: Hematopoiesis in humans
Lymphopoiesis is the differentiation and maturation of lymphocytes from HSCs in the bone marrow. Lymphoblast is differentiated into T lymphocytes, B lymphocytes, and natural killer cells. Complete maturation of T and B lymphocytes occur in thymus and spleen respectively. The maturation of T lymphocytes is called T-cell development and the maturation of B cells is called B-cell development. Granulopoiesis is the differentiation and maturation of granulocytes from myeloblast in the bone marrow. The three granulocyte lineages are neutrophils, eosinophils, and basophils. The presence of cytoplasmic granules and segmented nucleus in cells are the characteristic features of granulocyte lineages. Monopoiesis is the maturation of monocytes as a branch from the monocyte-granulocyte precursor. Differentiation of monocytes is done from monoblast. Thrombopoiesis is the production of mature platelets in the bone marrow. Megakaryocytes are the large cells which produce platelets by fragmentation. Platelets contain granules, which are released upon the activation of platelets in the process called platelet plugging.
What is Erythropoiesis
Erythopoiesis is the full maturation of erythrocytes from proerythroblasts in the red bone marrow. Proerythroblast contains a large nucleus and prominent organelles with no hemoglobin in the cell. During erythropoiesis, large amounts of hemoglobin are produced. Ultimately, erythrocytes lose their nucleus along with the intracellular organelles. During the differentiation, proerythroblast become smaller in size, organelles are lost, and the color of the cell is changed from blue to red. The blue color cells are called basophilic and the red color cells are called eosinophilic. The blue color is given by the hemoglobin-coding nucleotides and their decrement along with the increment of the actual proteinaceous hemoglobin give a pink color to the cell. The nucleus becomes small, compact and is ultimately excluded from the cell. Unmatured reticulocytes are released to the circulation from the bone marrow. The number of reticulocytes in the peripheral blood is an indication of the rate of erythropoiesis in the bone marrow. Reticulocytes are slightly basophilic. The process of erythropoiesis is regulated by erythropoietin, which is synthesized in the kidney in response to low oxygen tension in the blood in the arteries. Red bone marrow is shown in figure 2.
Figure 2: Red bone marrow
Difference Between Hematopoiesis and Erythropoiesis
Definition
Hematopoiesis: Hematopoiesis is the differentiation and maturation of blood cells from HSCs.
Erythropoiesis: Erythropoiesis is the differentiation and maturation of erythrocytes.
Types
Hematopoiesis: Five types are found in hematopoiesis: erythropoiesis, lymphopoiesis, granulopoiesis, monopoiesis and thrombopoiesis.
Erythropoiesis: No types of erythropoiesis are found.
First Committed Cells
Hematopoiesis: Proerythroblast, lymphoblast, myeloblast and megakaryoblast are the first committed cells of hematopoiesis.
Erythropoiesis: Proerythroblast is the first committed cell in erythropoiesis.
Regulation
Hematopoiesis: Hematopoiesis is regulated by a variety of growth factors.
Erythropoiesis: Erythropoiesis is basically regulated by erythropoietin.
Conclusion
Hematopoiesis and erythropoiesis are two pathways involved in the synthesis of blood cells. The differentiation and maturation of all blood cells is known as hematopoiesis. The differentiation and maturation of red blood cells is known as erythropoiesis. Hence, erythropoiesis is a type of hematopoiesis. Other types of hematopoiesis are lymphopoiesis, monopoiesis, thrombopoiesis, and granulopoiesis. Hematopoiesis is initiated from the progenitor cell, hematopoietic stem cell, which is capable of self-renewing and differentiating into all types of blood cells found in the circulation. The differentiation pathways are branched in the form of a tree. HSCs are found in the bone marrow of adults. Reticulocytes are released from bone marrow into the circulation during erythropoiesis, maturing in the circulation itself. The main difference between hematopoiesis and erythropoiesis is the resulting blood cells types from each pathway.
Reference:
1. “Hematopoiesis.” Hematopoiesis | Pathway Medicine. N.p., n.d. Web. 25 Apr. 2017.
Image Courtesy:
1. “Hematopoiesis (human) diagram” By A. Rad – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “619 Red and Yellow Bone Marrow” By OpenStax College – Anatomy & Physiology, Connexions Web site. Jun 19, 2013. (CC BY 3.0) via Commons Wikimedia
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