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Old 02-08-2019, 04:33 PM
Zyada Zyada is online now
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Are there any organs besides kidneys that we have a spare?

We have two kidneys, and I know that one can be donated to another person while you're still alive, because my SIL donated hers to her brother when they were young.

Are there any other organs that this could apply too? I know most of the other well-known organs are singleton. And I doubt anyone is going to give up an eye to help out someone else, no matter how much they are loved.

Might deserve another thread, but also what impact would donating a kidney have on your life expectancy?

Inspired by a reddit thread where a person had posted a photo of a car that was asking for a spare kidney for the owner's sister.
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Old 02-08-2019, 04:43 PM
senoy senoy is offline
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lungs
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Old 02-08-2019, 04:43 PM
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Eyes
Testes

Last edited by Channing Idaho Banks; 02-08-2019 at 04:44 PM.
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Old 02-08-2019, 04:49 PM
Jackmannii Jackmannii is online now
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Quote:
Originally Posted by Zyada View Post
Inspired by a reddit thread where a person had posted a photo of a car that was asking for a spare kidney for the owner's sister.
Was this My Mother The Car? Seems a little presumptuous...
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Old 02-08-2019, 04:57 PM
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Quote:
Originally Posted by Channing Idaho Banks View Post
Eyes
Testes
There are plenty of things we have more than one of, but I got the impression that the OP was looking for things where having more than one doesn't confer any additional advantage except that we have a spare in case we lose one.

Two eyes are better than one (better depth perception), but testes (or ovaries) might qualify.

Are we restricted to organs that are donatable (using current medical technology)?
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Old 02-08-2019, 04:58 PM
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One can donate part of the liver.

Also, veins and small intestine. Though they are usually transplanted into somewhere else on the same patient rather than someone else. (Veins are used for bypass surgery, intestine can replace the esophagus if you have esophageal cancer.)

Skin.

Last edited by scr4; 02-08-2019 at 04:59 PM.
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Old 02-08-2019, 06:16 PM
Zyada Zyada is online now
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There are plenty of things we have more than one of, but I got the impression that the OP was looking for things where having more than one doesn't confer any additional advantage except that we have a spare in case we lose one.

Two eyes are better than one (better depth perception), but testes (or ovaries) might qualify.

Are we restricted to organs that are donatable (using current medical technology)?

I was thinking more along the lines of donatable organs, especially something that you would need to get replaced if yours was damaged/diseased. Seems like ovaries and testes might qualify for being donatable, but are probably not actually needed for someone's continued health. Although their contents are fairly common donations!
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Old 02-08-2019, 06:21 PM
nearwildheaven nearwildheaven is offline
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Lungs come in pairs, and most people have 4 parathyroids, although that number can vary widely. We also have more bowel than we "need" (you can lose about half of it without adverse effects). Mammals also have twice as many breasts as their average litter size, which comes in handy when it comes to feeding them.

I've definitely heard of live-liver donation (usually done between first-degree relatives) but never heard of live lung donation. I did once read about a live heart donation; IIRC, a man with cystic fibrosis needed a lung transplant, and when the lungs are transplanted, usually the heart is too because they are so interconnected. Someone in the same hospital (!) was a good match and received that man's heart. I heard about it when I saw a news program where they met.

Last edited by nearwildheaven; 02-08-2019 at 06:24 PM.
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Old 02-08-2019, 07:05 PM
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One can donate part of the liver.

Also, veins and small intestine. Though they are usually transplanted into somewhere else on the same patient rather than someone else. (Veins are used for bypass surgery, intestine can replace the esophagus if you have esophageal cancer.)

Skin.
In the same (PUN ALERT!) vein, Tommy John surgery takes a tendon and moves it to the pitcher's arm.
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Old 02-08-2019, 11:14 PM
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Losing one lung, kidney, or eye is still an impairment to some degree (though you can live with it). And if I understand correctly, losing one ovary would mean only one fertile cycle every two months, instead of one each month, which would also be an impairment. But a man with one testicle functions in all ways just as well as one with two, making that the only organ I know of with a fully-redundant spare.
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Old 02-09-2019, 01:55 AM
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Do fingers and toes count as "organs" for this? I recall a case where a surgeon lost a thumb and had a big toe transplanted to take its place; it worked well enough that he could still do surgery, and since it was his own toe there were no rejection issues to deal with. EDIT: Also, sometimes nerves are transplanted from one part of a person to another, generally resulting in a small numb spot somewhere low priority while the transplanted nerve fixes something important.

We do have spare adrenal glands, but apparently nobody is even looking into transplanting them because medicinally replacing their function is so much safer and easier than dealing with rejection.

Quote:
Originally Posted by nearwildheaven View Post
I've definitely heard of live-liver donation (usually done between first-degree relatives) but never heard of live lung donation.
I have. I recall reading of a case where each parent of a child with cystic fibrosis donated a lobe of one of their lungs. The lobes would grow with the kid, and losing a single lobe wasn't too bad for the parents.

Last edited by Der Trihs; 02-09-2019 at 01:58 AM.
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Old 02-09-2019, 04:54 AM
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Nothing useful to add other than to recall that one day, some years ago, my father-in-law was telling my sister-in-law about a farmer friend of his who had a duck born with three legs. With wide eyes and mouth she took this in, churned it over for a few seconds and asked "what happened to the other one?"
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TWENTY-EIGHT YEARS OLD SHE WAS!!!!!!
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Old 02-09-2019, 09:57 AM
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Ears.
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Old 02-09-2019, 10:22 AM
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Ears.
How would your glasses stay on?
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Old 02-09-2019, 10:59 AM
Eva Luna Eva Luna is offline
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Also, veins and small intestine. Though they are usually transplanted into somewhere else on the same patient rather than someone else. (Veins are used for bypass surgery, intestine can replace the esophagus if you have esophageal cancer.)
Large intestine can also become bladder.
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Old 02-09-2019, 11:14 AM
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And if I understand correctly, losing one ovary would mean only one fertile cycle every two months, instead of one each month, which would also be an impairment.
Not according to several cites I've checked such as this:
Quote:
In this video, Jeffrey Hunter, MD, from West Valley OB/GYN, explains losing one ovary doesn't cause irregular periods. He says one ovary makes very little changes to a woman's cycle.
https://www.sharecare.com/health/gyn...egular-periods


Here's a quick explanation of why:
Quote:
While the body normally alternates which ovary releases an egg at ovulation, with one ovary, an egg is still released every month. Even if the ovary is not adjacent to its original fallopian tube, as long as there is a healthy tube on the other side, it is possible for the egg to reach it and then travel to the uterus.
But:

Quote:
However, the chances of a healthy pregnancy drop and the odds of ectopic pregnancy where a fertilized egg implants outside the uterus increase.
https://www.storkotc.com/blog/conceiving-one-ovary/

It's also been theorized that one ovary could result in a shorter reproductive lifespan.
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Old 02-09-2019, 11:21 AM
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...when the lungs are transplanted, usually the heart is too because they are so interconnected.
Heart-lung transplants are certainly done, but it's usually in cases where a lung disease has also caused a cardiac issue (pulmonary hypertension leading to increased right heart pressures and eventually permanent dysfunction, for example).

Single lung transplants are now pretty common in a variety of localized pulmonary disease states. They're a little less common than bilateral transplants in CF patients, but singles are still done in some CFers (patient, hospital, and situation specific).
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Old 02-09-2019, 11:22 AM
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Blood. You can donate about half a litre every few weeks.
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Old 02-09-2019, 11:26 AM
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Originally Posted by Chronos View Post
And if I understand correctly, losing one ovary would mean only one fertile cycle every two months, instead of one each month, which would also be an impairment. But a man with one testicle functions in all ways just as well as one with two, making that the only organ I know of with a fully-redundant spare.
Not so - losing either a single ovary or testicle has the same effect: not much.

(removed long explanation since x-ray vision beat me to it)

Tldr: reproductive organs are part of a complex and redundant feedback system.
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Old 02-09-2019, 01:19 PM
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Brains... some people don't use it.
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Old 02-09-2019, 02:59 PM
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Half my thyroid was removed, with no ill effects after 30 years or so.

In general redundant body parts would require energy, and that would be evolutionarily disadvantageous, especially in times of food shortages. So we'd expect that unless there was an advantage it would not be sustainable.
Consider computer systems. (I just wrote a column comparing the fault tolerance of the body to fault tolerance of computers.) Triple modular redundancy takes up space and energy, and so doesn't get used except in cases where reliability is really vital. Multiple core or processor systems are much more popular since they will still work if there is a failure but increase processing power even if everything is okay.
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Old 02-09-2019, 03:06 PM
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Not an organ but most people have a ~surplus tendon: the palmaris. It can be used for tendon grafts.
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Old 02-09-2019, 03:26 PM
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My left lung became messed up when I had TB as a young adult. I never noticed any real difference not using it.
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Old 02-09-2019, 07:09 PM
Tim@T-Bonham.net Tim@T-Bonham.net is offline
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It's called Bilateral symmetry and it applies to nearly all the human body (and also most mammals).

Look at the head, for example. Two eyes, 2 ears, 2 nostrils, 2 sinuses, 2 sets of teeth (sets of canines, incisors, bicuspids, etc. on each side), even 2 semi-independent halves of the brain (and you can live with only one)*. Many of the glands, like thyroids, lymph nodes are doubled. And the kidneys, as the OP mentioned. Even the critical heart has 2 halves, and people can live with only part of it working correctly. Most of the external body is so: 2 arms, 2 legs, 2 sets of fingers and toes.

Only when we get to the energy-production part (digestion) does the body limit itself to one: 1 tongue, throat, liver, stomach, intestine, colon, anus. (But note that this is way over-sized; people can lose way more than half the liver and still function; the stomach can be greatly reduced (gastric bypass/band), large sections of the intestines can be removed, etc.

In the most critical system (evolutionarily) of reproduction, we have fully redundant spares: 2 testes or ovaries, and still fully functional with one set gone.

So, in fact, it is more common for the human body to have 'pairs' of organs than not. So the OP's answer is 'most of them'.

* Evolution has started to take advantage of these 'spare' parts by doing some specialization in them. For example, the 2 halves of the brain tend to specialize in separate functions. Especially in right-handed vs. left-handed people. And that handed-ness itself is a bit of specialization from physically paired hands/arms.

Last edited by Tim@T-Bonham.net; 02-09-2019 at 07:11 PM.
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Old 02-09-2019, 09:33 PM
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OK, interesting, I stand corrected on the ovaries.
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Old 02-10-2019, 12:18 AM
whc.03grady whc.03grady is offline
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To expand on Tim@‘s asterisk up there, hemispherectomies are a thing.
https://my.clevelandclinic.org/healt...emispherectomy
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