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Harvard Commentaries on Health

Calling in the Replacements

The number of body parts that can be created, synthesized or replaced has grown rapidly over the last several decades. That's led to predictions that, eventually, all of our body parts will be replaceable. After all, who needs original parts when replacement parts work better and last longer? Does this mean that body parts that are replaceable are useless or that one day electronic body parts will replace the original ones?

Is a Bionic Human in Our Future?

As a kid, I used to hear often about the rapidly approaching reality of a "bionic" human. Television series (including The Six Million Dollar Man and its spin-off, The Bionic Woman) in the mid-1970s promoted this idea of super-heroes with bionic eyes, ears, arms and legs. This notion is still very much alive in action movies featuring human-machine hybrids such as Dr. Octopus in Spider Man 2.

The term "bionic" is a combination of "bio-," meaning living, and "-onic," referring to something electronic. The idea is that a person's body parts could be replaced or work better using an electronic device. A pacemaker is a good example of bionics at work.

In fact, a number of body parts can be replaced or transplanted by the miracle of modern medicine, though many are not "bionic." For example, a hip replacement isn't bionic as there are no electronic components.

Although the movies and television would have you believe otherwise, replaced parts rarely work as well as the original, healthy versions. For example, an artificial joint rarely has normal range of motion and recipients are routinely advised not to stress the joint too much with athletics or other activities. The stability and function of the replaced joint almost never matches that of a normal, healthy joint. The same can be said for artificial skin, dialysis machines and ventilators, which attempt to duplicate bodily functions but often fall short.

The notion that we will someday have totally "bionic" people or that our bodies will become readily replaceable part by part is a myth — at least for now.

The Most Commonly Replaced Parts

Replacement parts don't mean our original organs are useless, but they do mean that some parts are less vital than others.

Advances in modern medicine have made it possible for doctors to support many organs (as with a ventilator for lung failure) or to replace them entirely. Some are only temporary, some maintain life, and others improve quality of life.

Many come with their own set of problems. For example, would you rather have a kidney transplant and take potentially toxic medications for years or possibly the rest of your life to prevent rejection? Or, would you prefer to continue with dialysis three days a week for the rest of your life? Would you rather take pain medicines and continue limping with significant pain? Or, does it make more sense to endure a major operation to replace your worn out knee, knowing the operation can be risky and might not completely eliminate the pain? These are often tough decisions.

Here are some of the most commonly replaced body parts.

  • Joints – It's pretty hard to get around with a severely arthritic hip or knee. The loss of function and discomfort can dramatically reduce a person's quality of life. Fortunately, hip and knee replacement surgery is common now. Other joint replacements, including shoulders and ankles, are less common and less successful, but techniques are improving.

  • Bladder – For people with bladder cancer or other conditions, it may become necessary to remove the bladder. Surgeons can provide a "replacement" by using a section of the small intestine to store urine in much the same way the bladder does.

  • Skin – The most common way to replace burned or otherwise damaged skin is with a skin graft. Healthy skin from another part of the body is removed and placed in the area where the unhealthy skin was. A newer and promising technique grows skin cells outside the body and transplants them where damaged skin was removed.

  • Bone Marrow – Bone marrow transplantation was first performed in 1968. Since then the surgery has saved the lives of thousands of people suffering with leukemia or other blood disorders. The transplanted donor marrow can come from a sibling, another family member or an unrelated person who has certain genetic similarities to the recipient. In some cases, the person needing a bone marrow transplant can be his or her own donor by using cells collected when the blood disorder was in remission.

  • Kidney – When the kidneys fail, doctors can offer two ways to "replace" them. Dialysis simulates the blood-filtering function of the kidneys while a successful kidney transplant actually replaces the failing kidney with one that is healthy.

  • Lens of the eye – Cataract surgery to replace a cloudy lens with a plastic, acrylic or silicone lens is highly successful and common procedure that restores vision to millions of people worldwide each year.

  • Liver – The liver has a remarkable ability to withstand injury. In fact, it can regenerate a removed or injured part better than most tissues in the body. However, when a person's liver fails, doctors can transplant an entire liver from a person who has just died or transplant just a portion of a liver using part of a living donor's liver.

  • Lung – As with kidney failure, lungs that are failing can be "replaced" by a machine or by organ transplant. A ventilator (whether short-term or long-term) will breathe for a person when they cannot breathe on their own. A lung transplant is a better long-term option. In nearly all cases, the donor is someone who has just died.

  • Heart – Several "replacement" options are available. The choice depends on the cause. When the problem is a leaky or narrowed valve, the valve can be replaced with an artificial valve or one from a pig or from a person who has died. The coronary arteries that supply the heart muscle can be bypassed (using a transplanted vein or artery) or dilated. When heart disease affects the vital pumping action of the heart and medications are not helping enough, devices are available to temporarily support the heart. This includes the artificial heart which, so far, is not a long-term solution. If the heart function is permanently and severely impaired, a heart transplant is currently the only effective long-term solution.

An Artificial Brain?

At least one organ can't be readily repaired or replaced: the brain. It is the most "unforgiving" part of the body because it doesn't tolerate injury or regenerate on its own very well after an injury.

When repair or regeneration does occur in the nervous system, it's usually slow and incomplete. Sometimes, repair is nearly non-existent, as seems to be the case for so many stroke victims. To make matters worse, we currently have no machine or transplantable tissue to take over for the brain the way we do for so many other parts of the body.

In recent years, however, the ability to replace portions of the body (not just specific organs) has led to speculation about how far we can go. For example, surgeons have recently transplanted faces, arms, and a uterus.

Even so, until modern medicine figures out how to do a better job at replacing body parts and fix failing organs, and until we figure out how to make an "artificial brain" we are far from creating a bionic man or woman.

The Bottom Line

Replacement body parts and organ transplants have lengthened lives, improved quality of life and created a whole new set of problems and challenges. Even so, it's no small matter to have a joint replaced or a liver transplanted. It's major surgery with major risk. And, after a transplant, potentially risky medications are needed to prevent rejection. To make matters worse, people who need these procedures are often not so healthy to begin with — it's hard to get to the point of needing a vital organ transplanted while maintaining excellent overall health.

Although it's reassuring to know these "replacements" are available when needed, it is clearly best to do everything you can to keep your body parts in good working order. Perhaps someday in the future, even more body parts will be cloned, transplanted or built from scratch to replace a faulty original. For better or worse, the day of the bionic human will not arrive anytime soon.

Author: Robert Shmerling, M.D.
Date Last Reviewed: 1/12/2015
Date Last Modified: 1/12/2015
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