Red blood cells are produced in the liver, spleen and thymus during the fetal stage. Produced from bone marrow (erythroblasts or stem cells and hemocytoblast cells) from birth to 20 years of age. It is called erythroblast because it has a nucleus when it is produced in the bone marrow. The rest of the life is formed from the ends of the humerus, femur, sternum, vertebrae, vertebrae etc. The human body produces 400-500 ml of red blood cells every month. Every second, 10 million red blood cells are produced and 10 million are destroyed. It is destroyed in the liver and spleen. The kidneys secrete the hormone erythropoietin. The hormone erythropoietin regulates the production (more or less) of red blood cells. The process of making red blood cells is called erythropoiesis.