The process of Erythropoiesis:

The process of formation of mature erythrocyte/RBC  from its precursor cell is known as Erythropoiesis.

It takes place in bone marrow in adult life.But, it can occur in some other organs in gestational life,such as-

1) Yolk sac: Upto 2 months of gestation.(Mesoblastic stage)

2) Liver & spleen: 3-6 month of gestation.(Hepatic stage)

3) Bone marrow: Rest of the life.(Myeloid stage)

Erythropoiesis

Process:

1) Proerythroblast:

 It is the earliest identifiable stage of erythropoiesis. It is the largest cell in this series(15-20 um).The chromatin in opened up or fine in nature and cytoplasm is dark blue.There is presence of multiple nucleoli.

2) Basophilic erythroblast:

The nucleus becomes a bit condenced and the cytoplasm is slightly lighter in colou(12-16um)r.Nucleoli is barely visible. 

3) Polychromatophilic erythroblast:

Nucleus is a bit denser and the cytoplasm is grayish in color due to appearance of hemoglobin in cytoplasm.(12-15um).

4) Orthochromatic erythroblast:

Cytoplasm is pinkish and nucleus is pyknotic and eccentrically located(8-12um).

5) Reticulocyte:

Nucleus absent and cytoplasm is pinkish with slight bluish hue.Contains RNA material for hemoglobin synthesis.

6) Erythrocyte:

Mature form with central pallor.

For better understanding watch the following video on YouTube: