Topic 35- Erythropoiesis – Formation of Erythrocytes · Cytology · MU Pleven

Topic 35- Erythropoiesis – Formation of Erythrocytes

Hemopoiesis is the process of making blood cells
In the early embryo, blood cells arise from the yolk sac mesoderm
In the 2nd trimester, hemopoiesis occurs in the liver and little in the spleen
In the 3rd trimester, hemopoiesis occurs in bone marrow – major haemopoietic organ

All blood cells arise from a single major type of pluripotent stem cell in the bone marrow that can give rise to all blood cell types
These pluripotent stem cells are rare, but proliferate and form 2 major lineages of progenitor cells:
Lymphoid cells – lymphocytes
Myeloid cells – granulocytes, monocytes, erythrocytes, megakaryocytes

Progenitor cells for blood are commonly called colony-forming units (CFUs)
Four major types of progenitor cells/CFUs:
CFU-E (CFU-erythrocyte)
CFU-Meg (CFU-megakaryocyte)
CFU-GM (CFU-granulocyte-monocyte)
CFU-L (CFU-lymphocyte)
Haemopoietic tissues are blood-forming tissues, consisting of reticular fibres and specialized CT cells of mesenchymal origin
Two types of haemopoietic tissues:
Myeloid tissue – formation of most blood cells: RBCs, granulocytes, platelets
Lymphoid tissue – formation of T cells, proliferation of B cells, lymph nodes, and MALT
Periods of haematopoiesis:
Prenatal haematopoiesis
Mesoblastic (megablastic phase)
Hepatosplenic phase
Medullary (myeloid) phase
Postnatal haematopoiesis
Myeloid phase – in red bone marrow