How does splenic filtration affect reticulocyte maturation?

Reticulocytes are immature red blood cells that still contain small amounts of RNA. They are released from the bone marrow into the bloodstream, where they mature into full RBCs. The spleen plays a key role in this final stage of maturation through its filtration process.

As reticulocytes pass through the narrow passages of the spleen’s red pulp, they are physically “tested” for flexibility and structure. The spleen removes the last bits of RNA and any leftover cellular organelles in a process known as pitting. This transformation turns them into fully mature, smooth, biconcave red blood cells capable of efficiently carrying oxygen.

If the spleen is absent or not functioning properly, this final “quality check” step is skipped. As a result, immature reticulocytes may stay in circulation longer. This can cause a higher count of reticulocytes in the blood and the presence of abnormal RBCs, such as those containing small inclusions (like Howell–Jolly bodies).

So, the spleen doesn’t just remove old RBCs—it also fine-tunes new ones before they join the bloodstream. Its filtration ensures that red cells are perfectly shaped and flexible enough to move through tiny capillaries, maintaining smooth oxygen transport throughout the body.