currentsinbiology:

The Strange History Of The Spleen, The Organ That Can Replicate Itself

We know that while you’re still a fetus, the spleen makes red blood
cells. And as an adult, the spleen acts as a garbage can, filtering out
damaged blood cells and platelets. But you can live with some old broken
blood cells, so if you injured your spleen in the 1950s, doctors
wouldn’t waste time trying to stitch it up. They’d cut it out in a
splenectomy and send you on your way.

But modern imaging
technology has left us with a different picture of the spleen, realizing
that it has a role in the immune system. Blood slows down as it passes
through the spleen, which gives the immune system time to recognize and
make antibodies for certain types of bacteria.

When a spleen is injured, cells from the organ scatter throughout the
abdomen. If the cells are lucky enough to land somewhere with a lot of
blood vessels, they start to grow into tiny extra spleens called
splenunculi. The whole process is called splenosis, and it seems to be
pretty common: about 1 in 5 people have accessory spleens.