Organs With Plenty To Spare - Medical Myths - Harvard Commentaries

In my previous column, I talked about body parts that can be safely removed in adults without having a major impact on one's health or longevity. Examples included tonsils, the appendix and the gall bladder.

Many of our body parts come with more than is absolutely necessary. So if they have to be removed because of injury or disease, you can still be in good health.

Here are some examples of organs that have plenty of "reserves" or excess capacity:

Eyes — You can be perfectly healthy with one eye, although you may miss the depth perception and larger field of vision you have with two eyes. Losing both eyes also does not lead to poor health even though being blind can have a significant impact on your quality of life.

Ears — Hearing is not required for health although, as with sight, quality of life can be diminished by hearing loss. With only one ear, it may be more difficult to tell where a sound is coming from and the ability to hear faint sounds may be reduced, especially if it is coming from the affected side.

Digestive tract — Relatively large portions of the small and large intestines can be removed without having a major impact on overall health. In fact, the entire colon can be removed (in an operation called pancolectomy) without shortening a person's life. However, diarrhea and other digestive problems may develop that do have a significant impact on quality of life.

Kidney — Most people can live perfectly well with only one kidney. That's why people can donate a kidney. However, the risk of future kidney failure does increase somewhat as the remaining kidney must work harder. Also, without the usual reserve, an injury, infection or other damage to the remaining kidney can lead to kidney failure more quickly than usual.

Lung — When necessary, an entire lung can be removed. You can rely on the other lung and function perfectly well. A lung is usually removed due to a tumor, but occasionally it's done because of infection or emphysema.

Liver — A relatively large portion of the liver can be removed without major risk because there is so much "extra" liver tissue in reserve and because of its unique ability to regenerate itself after injury or removal.

Ovary and testicle — A single testicle can produce more than enough hormones and sperm to carry out its most important reproductive and hormonal functions. Similarly, a single ovary can make all the hormones needed and has more than enough eggs so a woman can still ovulate each month. In fact, the remaining ovary or testicle "compensates" for its missing partner.

Extremities — Many people have fewer than four extremities because of injury, surgery or developmental abnormality and remain quite healthy. Clearly, there are obstacles to overcome and losing an arm or leg affects quality of life.

Perhaps you've heard it said that you only use 10% of your brain or that half of the body's organs are not truly critical to life. While some body parts are clearly more vital than others, it's a myth that most of the brain goes unused. And no one would suggest parting with even the least useful organs unless there is a very good reason.

Still, it is true that we have many body parts that appear to have no role in maintaining health. What did your appendix ever do for you?

When it comes to giving up a non-vital body part the benefit may outweigh the risk. For example, there is some risk in having your appendix removed, but if it's inflamed, swollen and about to burst, there is a much bigger risk not having it removed.

Similarly, it's no small matter to donate a kidney to someone who desperately needs it. The surgery to remove your kidney has some risk and there is a small but real risk that you will develop problems in your one remaining kidney. But these risks may be worth accepting when a family member or friend is in serious need.

But that doesn't mean that your kidneys are unnecessary. If both kidneys were removed, only lifelong dialysis or a kidney transplant would keep you alive. Taken to an extreme, you could survive for quite a while without your spleen, most of your liver, your eyes, a lung, a kidney and an extremity or two. But that doesn't mean you don't need any of those things! In general, it's best to keep the parts you were born with if you can. Who knows? As our understanding changes over time, we may discover that the now "discredited" tonsil is vital after all!

While most people would not volunteer to have one of these parts removed, it's convenient that they're not vital. Millions of people worldwide owe their very survival to the ability to withstand removal of an organ, a limb or other body part due to disease or injury.

So, is it true that half of our organs are unnecessary? I suppose that depends on your definition of "necessary." You could probably live to a ripe old age missing half of your organs and all four limbs. But would you want to? There are factors to consider other than just survival. Quality of life matters! The next time someone tells you about all the unnecessary parts you possess, remind him or her of two important facts: It's generally best to keep the parts you were born with and, there may be reasons we are born with the full complement of body parts even if we aren't sure why.

Robert H. Shmerling, M.D. is associate physician at Beth Israel Deaconess Medical Center and associate professor at Harvard Medical School. He has been a practicing rheumatologist for over 20 years at Beth Israel Deaconess Medical Center. He is an active teacher in the Internal Medicine Residency Program, serving as the Robinson Firm Chief. He is also a teacher in the Rheumatology Fellowship Program.