Your Amazing Body
Science hasn’t uncovered every mystery about the human body, but what it has discovered will blow your mind
Science Knows Why ...
1. You get goosebumps. 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 at 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, goosebumps.
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 10, though they don’t fully emerge until young adulthood, which is when we (allegedly) acquire full-grown 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, USA 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 on to 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.
7. Your saliva tastes metallic right before you vomit. Saliva normally has a pH ranging from about six to seven, midway between acidic and alkaline. When you are about to throw up, your body produces more alkaline saliva, which tastes metallic, to neutralize the acidity of the vomit. If this metallic saliva happens on a consistent basis, you could be suffering from silent reflux, a condition in which stomach acid comes up into the back of the throat.
8. 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.
9. 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 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 is an irritation in the nose, triggering a sneeze.
10. 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.
11. You get that stomach-in-your-throat feeling on a roller coaster. When a coaster comes over a crest and plummets, the seat belt may keep your rear in place, but some loosely connected internal organs—such as your stomach and intestines—get a little ‘air time’. Your nerves detect the movement, which registers as the feeling that your stomach has jumped all the way into your throat.
12. You get a charley horse. ‘Charley horse’ is a nice nickname for a nasty muscle cramp, commonly in your calf. One study found that the nerves inside the muscle can fire up to 150 electrical charges per second during a cramp, which is what forces the muscle to squeeze so tightly. The potential causes include dehydration, overexertion and certain medications, such as diuretics.
13.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 sulphurous odour caused by the food’s sulphur-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.
14. You have an almost entirely new skeleton every 10 years. Old bone cells are constantly being replaced by new ones, a process called remodelling. This helps repair damage to the skeleton, and prevents the accumulation of too much old bone, which can become brittle and break more easily.
15. You blink constantly. The average person blinks 15 to 20 times every minute. Each time you blink, your eyelids spread a cocktail of oils and mucous secretions across the surface of your eyeballs to keep them from drying out. Blinking also keeps eyes safe from potentially damaging stimuli, such as bright lights, and foreign bodies, such as dust.
16. You shiver when you’re cold.“Your body is always trying to keep its temperature as close to 98.6°F (37°C) as possible,” says Rantala. “You shiver when you are cold in an effort to create heat” by contracting and expanding your muscles in quick bursts.
Body Parts You Never Knew Had Names
17. Pate: The crown of your head
18. Glabella: The smooth space between your eyebrows
19. Canthus: The point in the inner or outer corner of your eye where the top lid meets the lower one
20. Columella nasi: The skin that separates your nostrils
21. Rasceta: The horizontal creases on the insides of your wrists
22. Lunule: The crescent-shaped area at the base of your nail
23. Philtrum: The cleft between your top lip and your nose
24. Lingual frenulum: The membrane that attaches your tongue to the bottom of your mouth
25. Gnathion: The midpoint of your chin
26. Suprasternal notch: The depression below your neck between your clavicles (collarbones)
27. Acnestis: The area of your back between the shoulder blades that can’t be reached for scratching
28. Popliteal fossa: The back of your knee
Still Trying to Explain ...
29. 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. You may not need a uvula to speak English. But 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.
30. 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.
31. ‘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.
32. 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.
33. Random eyelid twitching. A twitchy eyelid can last anywhere from minutes to days. Most of these twitches are harmless and don’t affect your vision. “We don’t know why this happens exactly, but fatigue, caffeine and stress are common culprits,” says Rantala. Try applying a warm compress to your twitchy eye and gently massaging the lid with your fingers to relax the muscles.
34. Yawning. While there’s no shortage of theories, the true reasons for yawning remain a mystery. One theory suggests that the deep inhalation and short exhalation of a yawn increase blood flow to the brain, cooling it down. Another explanation is that a yawn gives your body a jolt, since your heart rate increases and your eye muscles tense up after you yawn.
35. Handedness. Animals other than humans, 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.
36. The appendix. Charles Darwin theorized 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.
37. 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.
38. The mesentery. In November 2016, researchers officially added another organ to anatomy textbooks. Scientists used to think the mesentery was a few unconnected sections of tissue scattered in the intestines. But after peeling back layers of the gut, they now realize it’s a single organ: a double fold of membrane in the digestive system that holds up the intestines, connects them to the abdomen and has a distinct, two-foot-long structure that spreads out like a Chinese fan. Its function? They still aren’t sure.
You’ll Be Amazed to Know That ...
39. Only one in 10 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 2.7 kilos of bacteria in a 90-kilo adult.
40. Your salivary glands produce four to eight cups 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 recognize them.
41. 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 centre of your wrist, below your palm. In humans, 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.
42. 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 4.5 to 5.6 litres of blood, and the kidneys filter about half a cup per minute.
43. Your skeleton contains a lot of water. The human body is mostly water (55 and 60 per cent for women and men, respectively). But that fluid isn’t just in your skin, muscles, and organs—it’s in your skeleton too. In fact, water makes up nearly a third of your bone mass.
44. The longest muscle in your body is named after a tailor. The name comes from sartor, the Latin word for tailor. Tailors used to sit cross-legged on the floor when they pinned hems or cuffs. That position required heavy use of the sartorius muscle, which ropes around your thigh from the pelvis to the shin bone.
45. 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.
46. The average human passes about 165 kilos of poop per year. Before you get grossed out, consider this medical wonder: A faecal transplant to help someone with a bacterial infection called Clostridium difficile—in which doctors take a healthy person’s poop and put it into the sufferer’s gastrointestinal tract—has a 90 per cent cure rate. That’s a higher rate than for treatment with an antibiotic.
47. 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. Scientists aren’t sure why, but only about 10 to 20 per cent of us are able to engage those muscles to wiggle our ears.
48. You can live without your stomach ... With some weight-loss surgeries and for some stomach cancers, patients might have part or all of their stomach removed. Once it is gone, surgeons will connect the oesophagus directly to the small intestine so food can be digested there.
49. ... and without your colon. The large intestine might be removed to treat colorectal cancer, Crohn’s disease or ulcerative colitis. A surgeon would either connect a pouch made of small intestine to your anus so you can pass stools or divert waste from the small intestine to an opening created in the abdomen, which would empty into a colostomy bag outside the body.
50. Your skin glows in the dark. A decade ago, Japanese scientists used ultrasensitive cameras to discover that humans actually 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 late afternoon, possibly because of changes in metabolism.