The human eye is capable of seeing some ultra-violet light but it is filtered out by the lenses in our eye. Painter Claude Monet had the lens of his eyes removed after developing cataracts. After the surgery, he started painting lilies that he had previously painted white before, as blue, leading to the idea that he could have been perceiving UV light, which most normal humans cannot.
2. We cry when we are happy because the hypothalamus in our brain can't tell the difference between being happy or sad.
3. When our inner voice speaks in our head, it is accompanied by subtle muscle movements from our larynx.
4. When you get sunburned, your skin cells don’t get damaged and die. What really happens is that the DNA of the skin cells are damaged by the sun and the cells then commit suicide to prevent themselves from turning into cancer, in a process called UVB-induced Apoptosis.
5. In 1991, Dr. J. Andrew Armour discovered that the heart has its own "little brain" and named it "intrinsic cardiac nervous system." This "heart brain" is composed of approximately 40,000 neurons that are similar to neurons in the brain.
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Up to 30% of humans have a second spleen called an accessory spleen. These are usually very small, but may grow and function when the main spleen is removed or damaged.
7. Pain is the only sensation a tooth can experience. When you eat or drink something too hot or too cold, or a dentist operates on your teeth, you will only experience pain because that is the only thing the nerves around your teeth respond to.
8. Immune cells in humans go through a series of trials in a small organ in our chest called the thymus, to make sure they do not recognize human cells as foreign. Any cells that fail these tests are forced to kill themselves. 98% of the immune cells in our body fail this test.
9. The feeling of ‘butterflies’ in your stomach is caused by a reduction of blood flow to the stomach due to your body’s fight or flight response. When human body releases adrenaline, it results in the release of huge amounts of glucose from the liver. It also pulls blood away from your gut and into your arms and legs, which is what causes the feeling.
10. Even if the stomach, the spleen, 75% of the liver, 80% of the intestines, one kidney, one lung, and virtually every organ from the pelvic and groin area were removed, the human body can still survive.
11Testicle Taste Receptors?
Other than the tongue, the human body also has taste receptors in the stomach, intestines, pancreas, lungs, anus, testicles, and the brain.
12. The speed of the airflow in your trachea when you cough is around 85% of the speed of sound.
13. The inside of the human small intestine has the same surface area as a tennis court.
14. The human stomach has more nerve endings than the spinal cord, giving a bit more meaning to gut feeling.
15. Humans can regenerate some of their organs through a process called "Compensatory Hypertrophy." When part of the liver is removed or destroyed, the remaining portion grows to the original size and allows the liver to function as it did before. Kidneys and lungs can also similarly compensate.
People without a functioning larynx can still speak without a mechanical voice box by using their esophagus to speak. ‘Esophageal speech,’ uses the esophagus to move air to produce vocalizations in individuals who have had their larynx (including vocal cords) removed. The skill requires a lot of practice but is a godsend to those who otherwise would not have a voice.
17. There is a protein made by placenta cells called syncytin which aids in the attachment of the placenta to the uterine wall, making it essential for nutrients to get to the developing fetus. The gene that codes for the protein actually came from a virus millions of years ago.
18. Post-workout muscles aren't sore because of lactic acid buildup. It’s a myth perpetuated by a doctor who experimented on a severed frog. Lactic acid is actually a fuel made from glucose and burned by the muscles to maintain energy. Soreness which is typically experienced post workout is from micro tears in the muscle and the resulting inflammation.
19. A person with damage to the right brain hemisphere can develop a "joke addiction," a compulsive need to constantly make jokes.
20. About 8-16% of humans are missing the palmaris longus muscle, which was once used for climbing.
Tight Pants Syndrome is a real health risk which can result in abdominal and chest pain and could also lead to “testicular torsion” in men. Testicular Torsion refers to the twisting of the testicle within the scrotum, which can lead to blood loss and if not treated within 6 hours, can result in loss of the testicle.
22. 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.
23. Human ear can't tell where low frequencies come from. This is why subwoofers can be hidden in home theaters or in trunks of cars.
24. Retinal is a photoreactor molecule present in the human eyes, but it has to leave the eye and be recycled through the liver once it has been exposed to light.
25. There is a valve in fetal heart that diverts blood away from the lungs while in utero. It begins closing as the baby takes its first breath after being born and gets oxygen from its own lungs for the first time.