Still useful after all these years: The spleen

While some anatomical organs are dismissed as totally unnecessary (see Still useful after all these years: The appendix), others are considered useful but dispensable. Consider the spleen.

Located on the left side of the body, under the ribs and behind the stomach, the spleen is about five to six inches long and one and a half inches thick. It weighs about six ounces (the weight of a can of tuna).

Until recently, we thought the spleen was limited to filtering out red blood cells and supporting the immune system.

What we already knew the spleen did for us

Red blood cell gets old, tired and damaged after 120 days or so, at which point we make new replacement cells. The spleen filters out the old blood cells. Not only does the spleen remove the aging cells. It recycles them. It breaks down the hemoglobin so the liver can use it for bile, and it makes the iron in hemoglobin available for the manufacture of new red blood cells.

In addition to filtering out old cells, the spleen removes bacteria from the blood. This is one part of the spleen’s immune system function. It also manufactures antibodies for fighting bacterial infections. It can produce new red blood cells — just like bone marrow — and it stores blood, releasing it if we lose blood due to an injury.

Life without a spleen

All this seems highly commendable, but it’s not enough to make the spleen an essential organ. We can live without it.

The spleen is vulnerable to rupture. This is usually the result of a car accident or a sports injury. Because the spleen has such an abundant blood supply, a rupture is a medical emergency. To stop the internal bleeding, surgeons remove the spleen.

Life without a spleen means greater susceptibility to infections, but there are antibiotics. There will be more white bloods cells and platelets in the blood, but not that many more. Some vaccines won’t be as effective without a spleen. It doesn’t seem like a big deal.

But medical science has known for some time that we’re definitely better off with a spleen than without one. There was a study published in 1977 that followed World War II veterans for over 20 years. It found that veterans who had lost their spleen in the war were twice as likely to die from pneumonia and heart disease. The pneumonia could be explained by the diminished immune response. But why the heart attack fatalities? This is where the most recent developments in our understanding of the spleen come in.

Finally getting some respect

When the body is seriously injured — a gaping wound or a heart attack — a type of white blood cell called monocytes rush to the injury and heal the damage.
Scientists used to think that these monocytes, which are produced in our bone marrow, were stored only in the blood. But it turns out, as many as half of the available monocytes are stored in the spleen.

Immediately after a heart attack, monocytes leave the spleen, move to the heart, and begin their repair work. They remove dead muscle cells, build scar tissue, and stimulate the growth of new blood vessels. If you’re missing 50% of these little helpers, your chances of surviving a heart attack go down. That’s why veterans without a spleen were twice as likely to die.

How could we not know this?

As Matthias Nahrendorf, the author of the new study on the spleen, remarked: “Often, if you come across something in the body that seems like a big deal, you think, ‘Why didn’t anybody check this before?’ But the more you learn, the more you realize that we’re just scratching on the surface of life. We don’t know the whole story about anything.”

Commenting on the study, Ting Jia and Eric G. Pamer point out: “[T]he spleen lacks the gravitas of neighboring organs [like the liver or the stomach] because we can survive without it.”

In an article in the New York Times, Natalie Angier compares underestimating the value of the spleen with the cavalier attitude doctors take to the “prophylactic” removal of a woman’s ovaries.

In recent years, for example, many older women undergoing hysterectomies have been advised to have their healthy ovaries removed at the same time, the rationale being: if you are past your childbearing years, why hang on to reproductive organs that might turn cancerous and kill you? Yet follow-up surveys have shown that women who underwent elective ovariectomy had a heightened risk of dying during a given study period, were more susceptible to heart disease and lung cancer and were twice as likely to develop Parkinson’s disease compared with women who had kept their ovaries. “Evolution has an edge on us,” Dr. Nahrendorf said. “I would be very careful about saying, ‘You don’t need this organ, get rid of it.’ “

Finally, Jeffrey Laitman, president-elect of the American Association of Anatomists, had this comment:

History is littered with body parts that were called “useless” simply because medical science had yet to understand them. People say, “You can remove it and still live.” But you have to be careful with that logic. You could remove your left leg and still live. But whenever a body part is moved or changed, there’s a price to pay.

So, always wear a seat belt to protect your spleen – and for many other good reasons. Natalie Angier suggests maybe our “little sports warriors” should start wearing appropriate protective gear. Now there’s a cause you might want to take up with your local school district.

Related posts:
The Spleen in Chinese Medicine
Still useful after all these years: The appendix
Still useful after all these years: The gall bladder
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