for National Geographic News
Appendix, tonsils, various redundant veins—they're all vestigial body parts once considered expendable, if not downright useless.
But as technology has advanced, researchers have found that, more often than not, some of these "junk parts" are actually hard at work.
Case in point: the spleen, which a new study shows may be critical in healing damaged hearts (interactive heart guide).
Sure, the spleen—kidney shaped and tucked into the upper left of your abdomen—helps spot infections and filters out red blood cells that are damaged or old. But overall the organ has been seen as nonessential. Cut it out, and people still live.
But the new study, to be published tomorrow in the journal Science, has uncovered another, more critical role.
How Do You Mend a Broken Heart?
Researchers studying mice discovered that the spleen stores monocytes, white blood cells essential for immune defense and tissue repair.
Previously, scientists had thought monocytes were made only in bone marrow, like other types of white blood cells, and were "stored" in the bloodstream.
But the new study found that the spleen contains ten times as many monocytes as blood—making it a far more important storehouse.
What's more, the spleen is the source of 40 to 50 percent of the monocytes involved in nursing lab mice back to health after a heart attack, said study co-author Filip Swirski of Massachusetts General Hospital's Center for Systems Biology in Boston.
"If you're going to survive a heart attack, your heart has to heal the proper way, and that depends on monocytes," Swirski said.
"It was thought that the monocytes that accumulated immediately after a heart attack were ones that had been circulating in the blood. But we did calculations and found that the number that accumulated in the heart far exceeded the number in circulation," he said.
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