Life Span and Destruction of Red Blood Cells

When red blood cells are delivered from the bone
marrow into the circulatory system, they normally circulate
an average of 120 days before being destroyed.
Even though mature red cells do not have a nucleus,
mitochondria, or endoplasmic reticulum, they do have
cytoplasmic enzymes that are capable of metabolizing
glucose and forming small amounts of adenosine
triphosphate.These enzymes also (1) maintain pliability
of the cell membrane, (2) maintain membrane
transport of ions, (3) keep the iron of the cells’ hemoglobin
in the ferrous form rather than ferric form, and
(4) prevent oxidation of the proteins in the red cells.
Even so, the metabolic systems of old red cells become
progressively less active, and the cells become more
and more fragile, presumably because their life
processes wear out.
Once the red cell membrane becomes fragile, the
cell ruptures during passage through some tight spot
of the circulation. Many of the red cells self-destruct
in the spleen, where they squeeze through the red pulp
of the spleen.There, the spaces between the structural
trabeculae of the red pulp, through which most of the
cells must pass, are only 3 micrometers wide, in comparison
with the 8-micrometer diameter of the red
cell. When the spleen is removed, the number of old
abnormal red cells circulating in the blood increases
considerably.