Re: When a red blood cell spits out its nucleus, where does the nucleus go?

After red blood cells are made in the bone marrow (inside your bones), they quickly lose their nuclei. They do this because they must be pliable and able to fold so they can enter the tiny blood vessels and capillaries that extend to the far reaches of the body. Also, as they travel through the blood, they must be able to fit through the tiny slits in the spleen which help to filter the blood. There are other kinds of cells in the marrow, called macrophages which specialize in eating up large things like cells, and in this case, red blood cell nuclei. The red blood cells don't need them in order to carry out their primary function which is to carry oxygen (O2) and carbon dioxide (CO2). One thing that they really need is to have the hemoglobin protein - the protein that makes the cells red and allows them to carry O2 and CO2. Frankly, this is not that complicated (for a cell) and a nucleus is not necessary in these cells - they have enough building blocks in them (RNA and proteins) to continue living for a long time (approximately 120 days). As far as knowing what to do, the cells just need to go with the flow created by the rapidly pumping heart.