Production of RBC in human body

Red Blood Cell Formation
The term erythropoiesis (erythro = RBC, and poiesis = to make) is used to describe the process of RBC formation or production. In humans, erythropoiesis occurs almost exclusively in the red bone marrow. (The yellow bone marrow is primarily composed of fat, but, in response to a greater need for RBC production, the yellow bone marrow can turn to red marrow.) The red bone marrow of essentially all bones produces RBCs from birth to about five years of age. Between the ages of 5 to 20, the long bones slowly lose their ability to produce RBCs. Above age 20, most RBCs are produced primarily in the marrow of the vertebrae, the sternum, the ribs, and the pelvis. Let's examine how RBCs are produced and, ultimately, how they are destroyed. The organ responsible for "turning on the faucet" of RBC production is the kidney . The kidneys can detect low levels of oxygen in the blood. When this happens, the kidneys respond by releasing a hormone called erythropoietin, which then travels to the red bone marrow to stimulate the marrow to begin RBC production.
The RBC lifetime is about 120 days.
a) Kidneys respond to a lower than normal oxygen concentration in the blood by releasing the hormone erythropoietin.
b) Erythropoietin travels to the red bone marrow and stimulates an increase in the production of red blood cells (RBCs).
c) The red bone marrow manufactures RBCs from stem cells that live inside the marrow.
d) RBCs squeeze through blood vessel membranes to enter the circulation.
e) The heart and lungs work to supply continuous movement and oxygenation of RBCs.
f) Damaged or old RBCs are destroyed primarily by the Spleen