Red Cells are bi-concave cells, with a diameter of 7mm, it contains hemoglobin and lacks a nucleus.
  Red cells (erythrocytes) are produced by the proliferation and differentiation of erythroblasts in the bone marrow . The earliest recognizable erythroid precursor is the pronormoblast.
  During erythroid maturation, the haemoglobin content of the erythroid cell increases so that by the reticulocyte stage, almost all of the cell protein is haemoglobin.