Red Blood Cells last an average of 120 days in the bloodstream. When Red Blood Cells age, they are removed by macrophages in the liver and spleen. A drop of blood can have a million Red Blood Cells. Each minute over a billion and a half red cells are replaced. Their job is to carry oxygen to the body's cells
It is not that a red blood corpuscle (RBC) does not ever have a nucleus. The RBC initially has a nucleus. However, as the RBC grows older, the nucleus size shrinks, and at full maturity, the nucleus vanishes. This may seem odd, considering the nucleus is considered the core of a cell. However, there is a strong reason why the nucleus disappears in older red blood corpuscles.
The RBC stores haemoglobin. Haemoglobin is a protein that keeps the oxygen bound to the RBC. When the nucleus is around, there is less space to store the haemoglobin. Once the nucleus starts shrinking, and finally vanishes, the space for haemoglobin storage, and subsequently increased oxygen levels in the blood increases. This is critical because it means that more amounts of oxygen can be transported through the blood to supply the different parts of the body. We depend on oxygen as our life source. Reduced or no nucleus essentially means more space for haemoglobin, and therefore more amounts of oxygen in the blood.
*** Your red blood cells are manufactured in your bone marrow. Once a new cell enters your bloodstream, it may circulate through your heart and body more than 100,000 times. Unlike other cells, red blood cells have no nucleus. This gives them more space to carry oxygen and makes them lighter, which helps your heart to pump trillions of red blood cells throughout your body. However, lacking a nucleus, they are unable to renew their internal parts.
** Thus, after about 120 days, your red blood cells begin to deteriorate and lose their elasticity. Large white blood cells called phagocytes consume these worn-out cells and spit out the iron atoms. The scarce iron atoms attach themselves to transport molecules that take them to your bone marrow to be used in the manufacture of new red cells. Every second, your bone marrow releases two million to three million new red cells into your bloodstream!
