Title: Erythroblastic island in bone marrow
Description: Scheme electron microscopy.
Different stages of maturing erythroblasts (2) are exposed in this scheme.
The centrally localized phagocytic reticular cell (1) has many long cytoplasmic extensions that forms a network with similar cells within the bone marrow. Its nucleus is irregular. The cytoplasm has a moderate amount of organelles however with a distinct variety of lysosomal structures (4).
At (5) a large phagolysosome is shown that contains an expelled nucleus of an erythroblast.
Different stages of maturing erythroblasts are spread around and close to the reticular cell.
(3): Indicates a proerythroblast (15-20 mm) with 2-3 nucleoli, large mitochondria and numerous polysomes.
(6): A basophilic erythroblast (12-18 mm) or early normoblast with clumped heterochromatin in the nucleus (mitosis) and numerous polysomes.
(2A): The polychromatic erythroblast or intermediate normoblast (10-12 mm) marks the onset of hemoglobin synthesis in the maturing stage concommittant with a general decrease in amount of all organelles. At this time nuclear clumping starts to take place.
At (2B) the orthochromatic erythroblast or late normoblast (8-12 mm) shows the early stage of extrusion of the pyknotic nucleus.
At (2C) an anucleate reticulocyte is shown close to an expelled pyknotic nucleus (2D).
Background: In the bone marrow close associations of developing red blood cells with reticular cells (1) are required during erythropoiesis. The CFU-S (colony forming units-spleen) or stem cell give rise to committed cells of the erythropoiesis the so-called BFU-E (burst forming units-erythroid) cells, then the small CFU-E (colony forming units-erythroid) lymphocyte-like cells and subsequently the proerythroblasts.
Keywords/Mesh: blood, bone marrow, erythropoiesis, reticular cell, phagocytosis, erythroblast, reticulocyte, erythrocyte, histology, electron microscopy, POJA collection