when does a red blood cell mature to lose it nucleus membrane

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Please find below the answer:

Erythropoiesis is the process of the formation of Red Blood Cells. In humans, RBCs are manufactured in the bone marrow. Initially immature RBCs have a nucleus. This immature cell slowly fills with hemoglobin until they are bright red reticulocytes ready to escape from the bone marrow into the blood capillaries to begin circulating around the body. The mature denucleated RBC then becomes ready to serve the purpose of carrying oxygen.

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