27 Amazing things your body does

1. You get goose bumps. When you feel a chill or see something scary, your body releases a surge of adrenaline. The point is to make your body hair stand up—which helped our animal ancestors stay warm and also made them look larger in the face of predators. Getting those individual hairs to stand to attention requires the teeny skin muscles at the base of each follicle to contract, making your skin look vaguely like a goose’s post-plucking—hence, goose bumps.

2. You grow wisdom teeth. Wisdom teeth are actually a third set of molars. They allowed our forebearers to munch on rough food such as roots, nuts, and meat, especially when other teeth fell out (alas, our ancestors had poor oral hygiene). About 35 per cent of people never develop wisdom teeth, partly because of an ­evolutionary shift that means the human jaw is often too small for them. The rest of us start developing them by age ten, though they don’t fully emerge until young adulthood, which is when we (allegedly) acquire some wisdom.

3. Your fingers and toes wrinkle in water. When you’re in the bath, water seeping into your skin makes the upper layers swell. That causes the blood vessels below to constrict, which in turn causes some of the upper layers of skin to collapse. The irregular pattern of swelling and falling skin is what we see as wrinkles on our fingertips and toes.

4. Your knees crack after sitting for a long time. The sounds you hear are probably caused by gas being released from the spaces between your joints—just like when you crack your knuckles. Meanwhile, muscles or tendons rubbing against your bones may also make your joints creaky. “We say motion is lotion,” Kim L Stearns, MD, an orthopaedic surgeon at Lutheran Hospital in Ohio, told the Cleveland Clinic. “When you’ve been sitting around, fluid in the joints doesn’t move. The more active you are, the more your joints lubricate themselves” and the less noise they will make. The popping shouldn’t alarm you unless it is accompanied by pain or swelling.

5. You get a stitch in your side from running. Starting a new exercise routine can cause pressure to push up from the abdomen or down from the lungs onto the diaphragm muscle between them. This restricts blood flow and causes the irritated diaphragm to spasm. Once your body gets used to exertion, side stitches should cease.

6. Your stomach growls when you’re hungry. When the receptors in the stomach walls sense an absence of food, they send out electrical waves. These cause the muscular walls of the stomach to squeeze and release, making a rumbling sound. You may also hear some sloshing as these contractions move water and stomach acid around inside.

7. You see spots after a camera flashes. The photoreceptors in the back of your eye convert light into electrical impulses that are sent to the brain to produce the images you see. “When a camera flash goes off, it’s so bright that it overstimulates the photoreceptors,” Elaine Icban, an assistant professor of clinical optometry at the New England College of Optometry, told statnews.com. While the photoreceptors are recovering, your brain “sees” nothing and fills in the blanks with spots.

8. You sneeze when you look up at the sun. Photic sneeze reflex—sometimes called sun sneeze—is the name of this peculiar phenomenon. “The optic nerve, which senses a change in light, is very close to the trigeminal nerve, which controls a sneeze,” says Amy Rantala, MD of the Mayo Clinic Health System in Eau Claire, Wisconsin. When you look up at the sun—or, for that matter, when you step out of a dark room into bright light, whether it’s artificial or natural—your optic nerve constricts your pupils. Your trigeminal nerve may get the sensation that there's an irritation in the nose, thus triggering a sneeze.

9. Each cell in your body endures tens of thousands of DNA lesions every day. Ultimately, this damage can alter a cell’s DNA and programme it to destroy body tissue, resulting in the disease we know as cancer. Luckily, your body also contains the first line of defence: enzymes are constantly checking DNA strands for signs of cancer and replacing damaged parts.

10. You might smell like a rotten egg after eating meat. Consuming too much meat (particularly red) plus an inability to digest it well can lead to a sulfurous odour caused by the food’s sulfur-containing amino acids. One small study found that women rated men’s body odours as more attractive, more pleasant, and less intense after they had eaten no meat for two weeks compared with when they’d eaten red meat, according to the University of California, Berkeley.

11. You shiver when you’re cold. “Your body is always trying to keep its temperature as close to 37°C as possible,” says Dr Rantala. “You shiver when you are cold in an effort to create heat” by contracting and expanding your muscles repeatedly in quick bursts.

12. The hanging ball at the back of your throat. Scientists don’t understand exactly what the uvula does, but because it is largely unique to humans, they suspect it plays a role in speech, possibly secreting enough saliva to lubricate the mouth while speaking and swallowing. For speakers of languages such as French and Arabic that use sounds known as uvular consonants (the r in the French word maître, for example), a missing uvula may alter their speech.

13. Hypnic jerks. An estimated 70 per cent of people have felt a sudden jerk right before they fall into a deep sleep. Research hasn’t pinpointed the reason behind these so-called hypnic jerks, but one theory is that as your breathing and heart rate slow down, your muscles start to relax and may twitch. It could also be that the brain sends a signal to your muscles to tense up because it mis­interprets their relaxation as a sign that you’re falling.

14. “Old-people smell.” A small study from 2012 confirmed that older people have a less intense­­ scent (some call it musty or grassy) than young and middle-aged folk. It’s not clear what causes this shift in odour as we get older, but researchers speculate that it might be due to a type of white blood cell supply that increases as we age.

15. Different blood types. Scientists aren’t sure why humans have different blood types. There does appear to be an association between blood types and certain diseases. For example, people with blood type A are at a higher risk for some forms of stomach and pancreatic cancer compared with people with blood type O, who are more likely to have ulcers and ruptured Achilles tendons.

16. Handedness. Other animals, including polar bears and chimpanzees, also have handedness, but those species are split 50/50 between right and left. Humans are the only ones that show a distinct bias as a species toward one hand (90 per cent of us are right-handed), and scientists have no idea why.

17. The appendix. Charles Darwin theorised that the appendix was the useless evolutionary remains of a larger structure that housed bacteria our plant-eating ancestors needed to digest stubborn plant tissues such as tree bark. Modern scientists aren’t convinced. Some think that the tube-like organ actually promotes the growth of some kinds of good gut bacteria.

18. Fingerprints. Our fingerprints are unique, though they do come in a few broad patterns: loops, whorls, and arches. Researchers have found that some patterns are associated with certain diseases—people with loop prints have a higher incidence of bronchial asthma and dementia, for instance. What we don’t know is why fingers have these swirly patterns in the first place. For many years, scientists thought they helped us grip things, but fingerprints actually allow less of our skin to come into contact with objects. Another theory: they somehow protect our fingers or provide touch sensitivity.

19. Only one in ten cells in your body is actually human. Of the 100 trillion cells in our bodies, the majority are microorganisms such as bacteria and viruses. In fact, the National Institutes of Health Human Microbiome Project found that micro­organisms make up about one to three per cent of the body’s mass, or as much as six pounds of bacteria in a 200-pound adult.

20. Your salivary glands produce one to two quarts of spit every day. Saliva breaks down food and keeps the mouth infection-free. Plus, without saliva, you wouldn’t be able to taste anything! Food molecules need to dissolve in saliva for taste buds to recognise them.

21. You might be missing an arm muscle. About 86 per cent of us have a palmaris longus muscle ­running from the elbow to the palm. To test whether you have it, touch your ­pinkie to your thumb and tighten your wrist ­muscles; a tendon connected to the muscle will pop out in the ­center of your wrist, below your palm. It helps wrist flexibility, but there’s no consequence if you’re born without one. Scientists aren’t sure why some ­people have the muscle and others don’t, but they think that it probably helped our primate ­ancestors grip and swing through trees.

22. Your heart can pump one ­million barrels of blood in a lifetime. Meanwhile, your kidneys filter your entire supply of blood more than 30 times every day. The average adult has 4.8-6 quarts of blood, and the kidneys filter about half a cup per minute.

23. Your lungs have an enormous surface area. Tiny air sacs called alveoli allow oxygen and carbon di­oxide to move between the lungs and the bloodstream. Average adult lungs have about 480 million alveoli, the surface area of which could cover half a ­tennis court.

24. The average human passes about 360 pounds of poo per year. Before you get grossed out, consider this medical wonder: A fecal transplant to help someone with an infection called clostridium difficile—in which doctors take a healthy person’s poo and put it into the sufferer’s gastro­intestinal tract—has a 90 per cent cure rate—a higher rate than with antibiotic treatment.

25. You might be able to wiggle your ears. Thirty million years ago, the three auricular muscles of the outer ear helped our evolutionary ancestors pivot their ears the way cats do. This movement doesn’t serve much purpose to modern humans—other than as a party trick. Only about ten to 20 per cent of us are able to engage those muscles now.

26. You can live without your stomach. With some weight-loss surgeries and some stomach cancers, patients might have part or all of their stomach removed. Once it's gone, surgeons will connect the esophagus directly to the small intestine to digest food there.

27. Your skin glows in the dark. A decade ago, Japanese scientists used ultrasensitive cameras to discover that human beings give off light, sort of like fireflies. Chemical reactions within our cells transmit a glow, mostly from the forehead, cheeks, and neck. The glow is faintest late at night and brightest in the late afternoon, possibly because of changes in our metabolism.

Read more: Delicious food combinations that boost weightloss

Read more: 10 Homemade sweet treats

Keep up with the top stories from Reader's Digest by subscribing to our weekly newsletter