Ask A Scienceblogger – Which parts of the human body could you design better?

i-133b9fea8ea6b307d8c9133b7f3e23bf-dice.jpg The question this month is “Which parts of the human body could you design better?”

This is a great question, because a lot of aspects of the human body represent what worked well enough for survival, not necessarily what works best. Therefore the engineering ends up being rather ramshackle, and convoluted, and sometimes, downright terrible.

For instance, who can look at this image – an anatomical model of human pregnancy at term, and not think this is really, really stupid engineering.

i-ec01c2239e3d4a89de41331d214c2397-Female reproduction.jpg
(image via wikipedia)

The very first thing I would change would be the female reproductive system. Ideally reproductive systems and waste removal equipment shouldn’t share space or have a such proximity to each other increasing risk of infection. The pelvis could do with some widening so women could actually deliver kids without killing themselves a significant portion of the time. Further, pregnancy in humans results in a fetus sitting on the bladder and colon for several months (and vaginal delivery acutely injures these muscles), as a result, post-partum many women have difficulty with urinary incontinence, and with age and with more kids the greater the risk of incontinence (this can not be prevented by c-section – so the damage is likely from positioning of the fetus on top of the bladder rather than acute trauma during birth). This unfortunate arrangement of the uterus appears to be a result of the change from walking on all fours to walking upright, the fetus, which would ordinarily sit mostly on the wall of the abdomen, ends up sitting directly on internal organs.

I’m sure women would like an alternative to monthly period as well. Overall though, the female reproductive system is terrible, involving significant risks of morbidity and mortality with each pregnancy. One of the great benefits of medicine has been the drastic reduction in infant and maternal mortality with labor and delivery – but it would be nice if the system were engineered correctly in the first place.

Much more below the fold…

The second thing I’d fix is several aspects of male reproduction. First, the prostate is a ridiculous organ, with a minimally-important function (secretion of prostatic fluid increases survival of sperm by a fraction), and a high propensity for developing cancer – I’d get rid of it altogether. The problem is that it’s a gland wrapped around a tube, and as you age it hypertrophies and prevents easy urination.

(image from wikipedia)

This is no longer a valuable contribution to our survival and reproductive efficacy, and I think most men would agree, we’d be happy with 1% less sperm in exchange for not having to pee in Morse code for the last 30 years of our lives. Alternatively, if it were just a gland in proximity to the urethra, rather than encircling it, we could enjoy its few benefits without having to suffer the side-effects (aside from inevitable prostate cancer). Also, in the image above, note the pathway of the vas deferens from the testicle to the prostate gland. This represents the pathway the testes take during development, which weakens the wall of the abdomen, leading to herniations as bowel can get stuck directly in the hole the vas deferens makes in the abdomen, or indirectly where the wall is weakened. The testes are also vulnerable, it’s unfortunate we have such delicate organs being kept in such an unprotected position – another consequence of bipedal motion.

The third thing I’d fix would be human aggression. There are socially maladaptive behaviors that were evolutionarily useful but now, not so much. Aggression, jealousy, selfishness. Mostly a problem of men, we are too violent and prone to rage.

Fourth, what ultimately kills is usually vascular disease. Atherosclerosis, which is what causes heart attacks, is actually a healing response gone awry. Here’s how it works.
(image from wikipedia)
As you age, lipids deposit in the walls of your arteries. This causes inflammation, white cells invade and try to digest the lipids, but this is ineffective and eventually a lesion forms that’s a mixture of lipids and white cells, and your body’s response is to just cover it all up with smooth muscle. This is called vascular remodeling, and it’s a modification of the normal healing process in blood vessels. You die when that nice layer of smooth muscle, that is covering up the inflammatory mess and necrotic tissue, fails or dies off. The inflammatory mess is suddenly re-exposed the bloodstream, platelets aggregate forming a clot, and all of a sudden a big chunk of your heart or brain no longer receives blood. This is the current model of myocardial infarction. The design flaw could be considered either the lipid deposition and inflammatory response, or the tendency of the recovery process to fail – the so-called “unstable” plaques that fail to hide the inflammatory mess from the bloodstream. Evolutionarily, this was a non-problem. Heart attacks kill you long after you’ve reproduced, so there isn’t a great need for this system to work perfectly. However, I think most of us would like to see an improvement so we can live long healthy lives. Similarly vessels that lose their plasticity with age, or arteriosclerosis, as well as a tendency towards higher blood pressure to compensate, could be improved thus preventing stroke.

Lastly I have a laundry-list of flaws in the design of various systems throughout the body. For instance:

The pancreas is a completely crummy organ, without a stem cell population to help regenerate it after being damaged, that eventually craps out in nearly every human with age. I would give the pancreas a stem cell population that renews the beta cells which are responsible for insulin production, and the whole insulin system could stand to be improved to prevent insulin insensitivity with age.

The combined openings for eating and breathing creates problems, with choking/aspiration risk. When you swallow, the trachea is blocked by the epiglottis:
(image from wikipedia)
That small fold of cartilage is all that keeps food from going down the wrong pipe. As with most systems in the body of combined function, I think this is non-ideal. Separation of function would decrease risk, but then we couldn’t use the tongue and lips for vocalization. So I don’t have a simple solution, but that doesn’t mean I have to like it.

A better system for bile storage, possibly signals to release it directly from the liver rather than making bile constantly and storing it in the gall-baldder, which allows stones to form and risks of things like cholecystitis and pancreatitis.

The sinuses are another atavistic feature. Our skull has many holes in it, which people who get sinus infections agree, are a giant inconvenience. Worse, the maxillary sinuses – which many people get infections in, drain upwards!
i-755eadcffd5efe211d642a413e9b6e36-Maxillary sinus.jpg
(image from wikipedia)
Do you see where the hole is? Isn’t that idiotic?
This is another consequence of holding our heads upright, the hole in the sinus is no longer in a position which facilitates easy draining of mucus, as a result, infections are common.

It’s unfortunate we can’t digest cellulose, like some organisms. That would greatly expand our diet and make vegetarianism more efficient.

Wisdom teeth are atavistic and worthless, causing pain. Or alternatively, our jaw is too small. Our teeth are also relatively weak and poorly oriented in many people, probably as a result of cooking food for thousands of years has put less emphasis of quality of dentition on survival.

Portosystemic anastomoses – at the stomach and anus, result in problems such as hemorrhoids and esophageal varices, which can be uncomfortable and deadly respectively.

The spine and pelvis modification that has allowed us to walk upright puts excessive force on the lumbar vertebrae- causing back problems.

Finally, we are unable to heal from amputations like some organisms. I want some salamander genes to regrow my limbs if they get cut off!

Of course I’d love to hear what other people think would be good to change. These are the main issues that I can think of that generate clinical problems in a great number of people.