The human body is a great, sweaty, fluid-filled machine, moving and mixing chemicals with precision and coordination, making everything from memories to mucus. Here we explore some of the complex, beautiful or just plain gross mysteries of how you function.
All skin, without coloring, would appear creamy white. Near-surface <a href=http://www.livescience.com/humanbiology/060619_synthetic_arteries.html target=new>blood vessels</a> add a blush of red. A yellow pigment also tints the canvas. Lastly, sepia-toned melanin, created in response to <a href=http://www.livescience.com/humanbiology/top10_burning_questions.html target=new>ultraviolet rays</a>, appears black in large amounts. These four hues mix in different proportions to create the skin colors of all the peoples of Earth.
Just as watching someone <a href=http://www.livescience.com/humanbiology/060817_brain_boot.html target=new>yawn</a> can <a href=http://www.livescience.com/mysteries/061113_yawns.html target=new>induce the behavior</a> in yourself, recent evidence suggests that <a href=http://www.livescience.com/humanbiology/061212_contagious_laughter.html target=new>laughter</a> is a social cue for mimicry. Hearing a laugh actually stimulates the brain region associated with facial movements. Mimicry plays an important role in social interaction. Cues like <a href=http://www.livescience.com/mysteries/061024_sneeze_eyes.html target=new>sneezing</a>, <a href=http://www.livescience.com/humanbiology/060331_laughter_good.html target=new>laughing</a>, <a href=http://www.livescience.com/mysteries/061019_cry_humans.html target=new>crying</a> and yawning may be ways of creating strong social bonds within a group.
<a href=http://www.livescience.com/evolution target=new>Evolution</a> isn't perfect. If it were, we might have wings instead of <a href=http://www.livescience.com/history/060405_neolithic_dentist.html target=new>wisdom teeth</a>. Sometimes <a href=http://www.livescience.com/animalworld/top10_vestigial_organs.html target=new>useless features</a> stick around in a species simply because they're not doing much harm. But wisdom teeth weren't always a cash crop for oral surgeons. Long ago, they served as a useful third set of meat-mashing molars. But as our <a href=http://www.livescience.com/humanbiology/060220_fish_brain.html target=new>brains grew</a> our jawbone structure changed, leaving us with expensively overcrowded mouths.
Most cells in our bodies sport hair-like organelles called cilia that help out with a variety of functions, from <a href=http://www.livescience.com/humanbiology/060328_bad_bacterial.html target=new>digestion</a> to <a href=http://www.livescience.com/humanbiology/060718_bad_hearing.html target=new>hearing</a>. In the <a href=http://www.livescience.com/humanbiology/050106_nose_smell.html target=new>nose</a>, cilia help to drain <a href=http://www.livescience.com/humanbiology/070117_sniffle_stopper.html target=new>mucus</a> from the nasal cavity down to the throat. Cold weather slows down the draining process, causing a mucus backup that can leave you with snotty sleeves. Swollen nasal membranes or condensation can also cause a stuffed schnozzle.
We know that hormone-fueled changes in the body are necessary to encourage growth and ready the body for <a href=http://www.livescience.com/humanbiology/060727_sex_history.html target=new>reproduction</a>. But why is <a href=http://www.livescience.com/humanbiology/050517_teen_thought.html target=new>adolescence</a> so emotionally unpleasant? Hormones like <a href=http://www.livescience.com/humanbiology/060814_testosterone_death.html target=new>testosterone</a> actually influence the development of neurons in the brain, and the changes made to brain structure have many behavioral consequences. Expect emotional awkwardness, <a href=http://www.livescience.com/humanbiology/060907_teenage_feelings.html target=new>apathy</a> and <a href=http://www.livescience.com/humanbiology/050517_teen_thought.html target=new>poor decision-making skills</a> as regions in the frontal cortex mature.
When a woman reaches her late 40s or early 50s, the monthly <a href=http://www.livescience.com/humanbiology/ap_060522_menstrual_end.html target=new>menstrual cycle</a> that controls her hormone levels and readies ova for insemination ceases. Her ovaries have been producing less and less estrogen, inciting physical and emotional changes across her body. Her underdeveloped egg follicles begin to fail to release ova as regularly as before. The average adolescent girl has 34,000 underdeveloped egg follicles, although only 350 or so mature during her life (at the rate of about one per month). The unused egg follicles then deteriorate. With no potential pregnancy on the horizon, the brain can stop managing the release of ova.
Though it makes up only 2 percent of our total body weight, the <a href=http://www.livescience.com/mind/ target=new>brain</a> demands 20 percent of the body's oxygen and calories. To keep our noggin well-stocked with resources, three major cerebral arteries are constantly pumping in oxygen. A blockage or break in one of them starves brain cells of the energy they require to function, impairing the functions controlled by that region. This is a <a href=http://www.livescience.com/mysteries/061214_stroke.html target=new>stroke</a>.
In addition to supporting the bag of organs and <a href= http://www.livescience.com/humanbiology/050216_young_blood.html target=new>muscles</a> that is our <a href= http://www.livescience.com/php/trivia/?quiz=bodyquiz1 target=new>body</a>, <a href= http://www.livescience.com/humanbiology/060509_growing_bones.html target=new>bones</a> help regulate our calcium levels. Bones contain both phosphorus and calcium, the latter of which is needed by muscles and <a href= http://www.livescience.com/humanbiology/060131_pain_truths.html target=new>nerves</a>. If the element is in short supply, certain hormones will cause bones to break downï¿½upping calcium levels in the bodyï¿½until the appropriate extracellular concentration is reached.
Can't remember your anniversary, hubby? Try getting down on one knee. <a href=http://www.livescience.com/memory/ target=new>Memories</a> are highly embodied in our senses. A <a href=http://www.livescience.com/humanbiology/060118_armpit_odor.html target=new>scent</a> or <a href=http://www.livescience.com/humanbiology/050526_music_memory.html target=new>sound</a> may evoke a distant episode from one's childhood. The connections can be obvious (a bicycle bell makes you remember your old paper route) or inscrutable. A recent study helps decipher some of this embodiment. An article in the January 2007 issue of <i>Cognition</i> reports that episodes from your past are remembered faster and better while in a body position similar to the pose struck during the event.
There's one dangerous liquid no airport security can confiscate from you: It's in <a href=http://www.livescience.com/humanbiology/060601_gut_microbes.html target=new>your gut</a>. Your stomach cells secrete hydrochloric acid, a corrosive compound used to treat metals in the industrial world. It can pickle steel, but mucous lining the stomach wall keeps this <a href=http://www.livescience.com/humanbiology/060105_stomach_bacteria.html target=new>poisonous liquid</a> safely in the digestive system, breaking down lunch.