The Human Body: 40 Little Known Facts – Part 3

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Drinking lemonade helps keep kidney stones from forming. It is useful if you are prone to kidney stones.

2. Human kidneys can only make urine that is less salty than salt water. Therefore, to get rid of all the excess salt taken in by drinking seawater, you have to urinate more water than you drank. Eventually, you die of dehydration as you become thirstier.

3. During the embryo development, 3 sets of kidneys develop, but only two remain to become the permanent adult kidneys.

4. You urinate more when you’re cold because of an increase in your arterial blood pressure caused by blood being taken away from your extremities and crammed in your core. Your kidneys shed fluid to try and stabilize it.

5. If kidney cells didn’t have aquaporins, which allow cells to reclaim water from urine, humans would have to excrete about 180 liters of urine per day.

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6Bladder Capacity

Bladder Capacity

Humans usually get the urge to pee when the bladder is just 1/3 full. But in zero gravity, the urge doesn’t kick in till the bladder is almost completely full. When John Glenn orbited the Earth, his only urination was measured at 27 ounces, seven ounces more than the capacity of an average human bladder.

7. The number of sweat glands you have is directly related to the temperature you experienced as a baby.

8. Kegel exercises can be beneficial for men as well. Men who do Kegels tend to have stronger erections and orgasm. They typically last longer in bed, have an increase in angle of erection and develop increased bladder control.

9. “Morning wood” occurs during REM sleep when certain neurotransmitters slow down which normally control blood flow. Morning wood also helps with bladder control at night.

10. Medical doctor Donald Unger cracked the knuckles of his left hand every day for more than 60 years, but he did not crack the knuckles of his right hand. No arthritis or other ailments formed in either hand, earning him the 2009 Ig Nobel Prize in Medicine.

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11Margarita Dermatitis

Margarita Dermatitis

If you leave the lime juice on your hands on a sunny day, your skin can get second-degree burns and be discolored for years. It’s called “margarita dermatitis” because people often get it while making margaritas outside.

12. Human fingers can feel objects as small as 13 nanometers. This means that, if your finger was the size of the Earth, you could feel the difference between houses from cars.

13. Fingers prune underwater not because of them absorbing the water or washing away the oils, but because of an evolutionary trait caused by the brain to enhance the grip of your fingers underwater.

14. The white spots on fingernails are called Leukonychia and are harmless. They are most commonly caused by minor injuries that occur while the nail is growing. Contrary to popular belief, leukonychia is not a sign of excess or deficiency of calcium and zinc or other vitamins in the diet.

15. Before medical science discovered how the circulatory system functioned, people believed that a vein ran directly from the fourth finger on the left hand to the heart. This is why people wear their wedding ring on this finger.

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16Human Fingers

Human Fingers

Humans finger contain no muscles and are controlled by muscles in the arm and palm pulling on tendons.

17. Wheelchair athletes with spinal injuries will sometimes intentionally injure themselves on the lower body (e.g. break a toe), causing their bodies to respond by raising blood pressure and enhancing their performance. This practice has been banned and is labeled cheating.

18. It’s possible to replace a lost thumb with a toe. The first successful toe-to-thumb transplant was performed in 1964, on a rhesus monkey (the first human was 1972).

19. There is a condition called ‘dactylolysis spontanea’, where a person’s toe just randomly falls off, and doctors have no idea why it happens.

20. When you give a thumbs up, the divot at the base of your thumb and wrist is called a “snuff box” ( anatomical snuffbox is the actual medical term).



Pain signals sent by an irritated diaphragm will be felt in the shoulder. The stabbing sensations near the heart that are sometimes felt after consuming a fatty meal are often confused with heart attacks but are nothing more than symptoms of indigestion.

22. Humans are unlikely to sink entirely into quicksand due to the higher density of the fluid. Quicksand has a density of about 2 grams per milliliter, while human density is only about 1 gram per milliliter. A human would descend up to their waist, but no further.

23. The human genome is comprised of 5% - 8% viral DNA, which can be traced back to 30-35 separate viral invasions in human history.

24. Only one person is recorded to have been cured of HIV/AIDS. In 2006, a patient from Berlin received a stem-cell transplant from an HIV-resistant donor, in-part to treat his Leukemia. He has been HIV-free since then.

25. When people are electrocuted and thrown far distances, it is a result of sudden and violent muscle contraction and not the result of the shock. This has raised questions as to the actual strength and capabilities of the muscles in the human body.

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