Location of Cells within Cord
Within the hematopoietic cords each cell line has a specific location for development.
Erythroid precursors are located near a venous sinusoid and cluster around a macrophage. This is referred to as an erythroblastic island. Developing red cells obtain iron needed for hemoglobin production from macrophages.
Megakaryocytes are also located close to a venous sinus. They extend their cytoplasm in fingerlike projections through the sinus wall in order to release their platelets directly into the blood in the sinus.
Immature granulocytes lie within the hematopoietic cords.
The metamyelocyte stage is the first stage of the granulocyte series that is motile and able to move toward the sinus area. Mature neutrophils, eosinophils and basophils enter the sinusoidal blood through the basement membrane. As maturing erythrocytes also move toward the sinus wall any remaining nuclei are lost as the red cells move through small openings in the cells lining the sinus wall.
