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A Documentary by the National Geography The incredible journey of life from birth, infancy, childhood, puberty, adulthood and the slow maturity to old age. . . This is the story of our lives from a unique perspective deep inside our bodies. A fetus develops in the womb. It is an astonishing 40-week journey from a single cell to a baby ready to be born. Its body is a miracle of microscopic design… tiny perfectly formed organs… each made up of perfectly functioning cells. These cells are the building blocks of our bodies. They make up what we are. A hundred thousand billion cells… all a ll working in harmony. Inside every cell is the the same extraordinary engine… the machine that tells each cell how to grow and what functions to perform. DNA is un ique to every person. A chemical blueprint of instructions that creates cr eates each new life. This baby is ready to enter the world… a new born person pe rson whose journey is about to begin. The journey starts with a challenge – breathe or die. These lungs never breathed before, they’re still full of amniotic fluid that protected them for 9 long months. The new born is in i n danger of drowning. Then body kicks into survival mode. The adrenal gland right above the kidneys sends adrenalin surging around the body. It shocks the lungs into life. Muscles we need to breathe suddenly start to spasm… spasm… and we take our first breath. It is the most important breath of ou r life… the first of 700 million. Our lungs will pump air every single second as long as we live. Air rushes down the windpipe down thousands of branching tubes and into nearly 30 million tiny air sacs (the alveoli). These air sacs pour oxygen into our blood and pump out the carbon dioxide we exhale every breath. At the moment of birth, everything changes. The physical link between mother and baby is broken for the first time. The first hour brings a rapid change. All the baby’s organs have to adapt to life life outside the womb. It is a challenging and risky time. At this age, the heart is no bigger than a walnut. The heart is normally working… pumping blood through thousands of miles of blood vessels. Other systems are also gearing up. The digestive tract is ready to clear itself out to make room for its first meal. The bowels are full of digestive amniotic fluid and dead cells – a sticky green-black tar-like material called meconium. As time passes, more sophisticated systems start to kick in. Our next challenge is the cold. It was a hundred degrees in the womb. Here at home, 65 degree room temperature is a shock to the system. The area that controls temperature is deep within the base of our brains. It is called hypothalamus.
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Like all other organs, at this age, it is still immature. The brain is under pressure making 100 trillion calculations per second just to keep our bodies functioning. But it is still learning how. And now, we’re in danger of hypothermia. A layer of specialized tissue around our blood vessels and vital organs actively generate heat. It is fat but this is not a regular fat. It is a brown fat usually found in hibernating animals. It is packed with special heat generating cells. Eventually, most of these fats will melt away as the hypothalamus matures and the liver and the other organs take on the job of generating heat. Just hours old, we know almost nothing about the world. Everything we do relies on instinct. Feeling is a reflex. Normally we have no more control over sucking than the urge to breathe. Outside of the womb, bacteria are everywhere, invisible and potentially deadly. Our skin is under constant attack. There are 10 times more bacteria than human cells in and on our bodies. Our immune systems are not developed yet so we cannot fight infections for ourselves. Amazingly, our mother fights them for us through her milk. The close contact between mother and baby means she absorbs the same germs that are attacking us. Her immune system creates antibodies then she delivers those antibodies back to us in her milk. Until our immune systems develop, she will keep us safe. It is time to take in the world. It has been 4 weeks since birth. It is time for its first trip outside. Even the visit to a grocery store can overload the senses. It is noisy, bright and smelly. The nose is working overtime. High up inside, specialized nerves dangle in the air stream. They detect chemicals in the air and send electrical signals to the brain which interprets the signals as smells. The nerves are super sensitive. Every smell is a new sensation. The same goes for our hearing. Strange new world… strange new sounds. Sound waves vibrate the eardrum. On the other side of the eardrum, these tiny bones (the ossicles) vibrate and respond. They are the smallest bones in the body but without them we would never hear a thing. They use leverage to amplify the vibration hitting the eardrum 22 times. The amplified vibrations now enter the inner ear or cochlea. It is lined with delicate hairs. When vibrations pass through, the hairs vibrate. At the base are the fragile hairs for high frequency sounds. At the top, low frequency hairs. Each one, 200 times thinner than a hair on our head. Over time, loud noises will damage these hairs but at this age, they are perfect. Our hearing will never be this good again.
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The story is different for eyesight. We are born with very underdeveloped vision. Even at 1 month, the world is blurred and mostly black and white. The eye muscles are immature keeping us from pointing our eyes where we want to. Inside the eyes, the lens muscles still cannot focus, and the lens flip the image it receives. All through life we see the world upside down. The picture only get reoriented in our brains, Right now, the picture is on the retina (the screen at the back of the eye). The retina has 2 kinds of cells – rods and cones which transform the light that hits them into electric signals. The cones detect color information but because they are not developed yet, we see mostly in black and white during our first month. From the retina, the signals will go along two thick nerves under the brain. At the back is where we process visual information. When the image arrives, the real challenge begins. Our immature brains haven’t learned to interpret the data yet. At 2 months, we can distinguish colors and shades. At four months, we can identify our mother’s face. By 8 months, we have a 20-20 vision. Along with our perfect eyesight comes a growth birth. We add a quarter to our body weight every month. After 3 months, it slows down. Lucky for us, if we kept growing that fast, we weigh 150 tons by age of 4, the same as a blue whale. At eight months, all our senses work. We are beginning to explore the world and the sense we use most is touch. Touch something so hot and temperature sensors in the skin send nerve signals rising up the arm, up the spinal cord and into the brain. All at 200 miles per hour. The brain detects the signal. Interprets it as pain and fires another signal back to the muscles. We move the hand away. We have sensory nerve receptors all over the skin. But some areas are sensitive than others – the hands, face, and mouth. There are 9,000 sensory receptors on the tongue alone which is why babies use their mouths to explore. But there’s another reason for all the annoying. Something is painful inside baby’s mouth. Her first teeth are coming through. Milk teeth formed deep our gums while we are still in the womb. Now, one by one, they burst through. It is painful but it is progress. At 8 months, the senses are working at full capacity. Every sensation is a new surprise. With her new teeth, she can take on solid food. Digestion starts in the mouth. Teeth grind up the food then specialized glands under the tongue pump out saliva to help break down and lubricate the food. On its 12-hour… 13 foot journey through the gut it will pass on the stomach into the coils of the small intestine before finally passing into the large intestine. Waves of contracting muscles keep the food moving. A process called peristalsis. This contraction is so powerful and you can eat even upside down. Food enters the stomach through a hole at the top.
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The stomach is a bag of muscle that churns, squashes, and squeezes food into liquid. At the same time, acids break the food down. The stomach walls protect themselves with a lining of mucus. Without it, the acids could digest parts of the stomach itself causing stomach ulcers. About an hour later, the stomach squeezes the broken down food out through a tiny hole called pyloric sphincter. Then food enters the small intestine (an eleven feet coil of tube) where we absorb most of the nutrients. The interior wall of the small intestine is lined with millions of microscopic projections called villi. The villi increase the surface area of the gut making it easier to absorb nutrients. First, the pancreas pumps out a juice that neutralizes stomach acid. Then bile from the liver breaks down fats into tiny droplets. After an hour and a half, the small intestine has absorbed most of the nutrients from the food. It is time for what remains to move on. It enters the large intestine through a sphinter . What is left is a mixed of waste food and dead cells from the walls of the gut. The large intestine’s main job is to extract water from it. Lots of bacteria live here too but it is not because of an infection. We actually need them. They produce enzymes that breakdown complex carbohydrates in our food. Carbohydrates we could not otherwise digest. Finally after about 12 hours, we expel what is left of our first meal. One year old… we have perfected the art of crawling. Our bones are stronger. They need to be because we are getting pretty heavy. At birth, the skeleton is mostly cartilage – the same material as our ears. Cartilage is flexible. It is what allows us to squeeze through the birth canal. After birth, our soft skeletons are our problem. They need to be rigid to support our growing bodies and protect our vital organs. So right from birth, the cartilage starts to harden. Special cells called osteoblasts lay down minerals that turn soft cartilage into hard bone. Some bones even fused together. At birth, we had gaps between the plates of the skull which may cause the skull to deform during birth. Through our first year, these gaps gradually close until the skull is finally complete. We are about to hit one of the major milestones in life – standing on 2 feet. The key is balance. The secret to standing is hidden deep in our ears. Beyond the ossicles (the bone we use for hearing), the inner ear is made up of 3 lopping structure. Each lope is the size of a dime and they are oriented to cover 3 plains. These semi circular canals are part of our ears but they have nothing to do with hearing. They are filled with liquid and they tell us what is up… what is down… and what is on the level. The liquid inside lashes sensory hairs lying the tubes. The hairs send data to the brain about how we are oriented and our direction of movement. These are the organs of balance.
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Age 2… talking takes a lot of brain power. A 2-year old learns 10 words a day. This is a Broca’s area, the region at the side of the brain use for speech production and comprehension. Language is what separates us from other animals. We exchange complex thoughts and ideas. Teach our children not just by showing but by telling. As our brains develop, we gain other uniquely human qualities. We are aware of our own identities and individuality. We gain the ability to think ourselves and form memories that will last a lifetime. Like our first day at school. We may know what was going on around us but the real action is happening inside. The brain is a mass of 100 billion nerve cells. Between them they generate enough electricity to keep a light bulb burning for a day. The cells communicate using electric impulses. Each impulse is a tiny fragment of memory or thought. When we hear a new word, our ears convert the sound into electrical impulses in our brains. The brain can learn because the connections between the brain cells are not permanent. The brain rewires itself. The cells meet at a tiny gap called synapse. Chemicals bridge the gap to allow the impulse to continue the chain. The new connections form a new pattern… a new memory. We learn by making new connections between brain cells and then reinforcing them through repetition. The stronger the reinforcement, the more likely the memory will stick. When someone asks us to recall that memory, the same pattern of axons fires and the memory comes alive. Our brains respond by sending messages to the nerves that drive muscles in our arms… we raise our hands. In childhood, our brains are very much open to learn. The rapid growth allows our brains to easily form connections – an ability that will fade in age. While our brains keep learning, our bodies do the same. It is the immune system’s job to learn to recognize infections. Every germ that enters our body carries the potential threat of disease. But first, the germ has to get there. Immunity does not begin inside our bodies. We start fighting germs the moment they touch us. We have an arsenal of defenses against infection. Our eyebrows and eyelashes… ear hairs…. and nasal hairs catch air-borne bacteria. Sweat, tears and mucus wash them off. Our skin constantly sheds its top layer of cells taking bacteria with it. The mouth is especially vulnerable. Here too, we are armed and ready to fire. Each squirt of saliva contains lysosome and enzymes especially targeted to destroy bacteria. Our saliva glands are tiny yet they produce nearly half a gallon of saliva every single day. Sometimes a pathogen breaks through this external defenses and our immature immune system reacts to prevent infection. Tiny viruses travel through our blood. The virus highjack the cell and manufacture a thousands of copies of it. Then the infected cells rapture spreading more viruses around the
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body. This particular virus causes a rash – chickenpox. The fever that comes with the infection is a sign that the body is fighting back. Heat slows down the spread of the disease because viruses don’t reproduce well when it is hot. The immune system kicks into action. While blood cells launch on into an infected cell and pump in poisonous proteins which kills the cell and the viruses. The skin blisters signal the battle range between the immune system and its viral assailants. Each one contains cellular debris and the remains of thousands of viruses. It may be unpleasant but getting diseases like this when we were young is vital for our developing immune systems. Our bodies create memory molecules (the antibodies) against the virus. We use to rely antibodies from mother’s milk. Now we can make our own. If we catch the same disease when we are older, the antibodies enable our bodies to recognize the virus instantly. White blood cells wipe it out before it has a chance to take hold. This is why childhood is the perfect time for vaccination. Vaccines are harmless doses of viruses like mumps, polio, or rubella. The body creates antibodies as if it had really been infected. Now if ever we catch the real thing, the body will recognize it and attack. Puberty… By age 11, puberty is already on the way for most. But there is no schedule. For some, it happens later… some, earlier. It depends on our DNA clocks… our lifestyles… and even our diets. Whether 10 or 13… female or male… puberty begins in the brain for all of us… at the base - the hypothalamus. It is the same region that controls our body temperature. Puberty starts when the hypothalamus releases a protein, kisspeptin, into the brain. The kisspeptin triggers the release of other hormones in a chain reaction throughout the body. Only then that our sex organs begin to mature. In girls, that means ovulation. During ovulation, an egg bursts from the ovary and travels down the fallopian tube to the uterus. From now until menopause, the same thing will happen every month. Then menstruation clears the uterus of unfertilized eggs. The ovaries not only produce eggs. They also produce potent cocktail of chemicals. They release hormones into the blood stream including estrogen. These hormones have dramatic, lasting, emotional, and physical effects. Male brains also produce kisspeptin to trigger puberty. A flood of new hormone stimulates the testicles to produce sperms. The testicles also generate testosterone - hormone producing physical characteristics of men. The larynx opens up and tilts forward. The vocal cords stretch wider. The longer cords vibrate at a lower pitch, the voice deepens. Testosterone stimulates the growth of the body hair and doubles muscle mass including 40% more heart muscle. In the brain, nerve cells undergo extensive rewiring transforming our mood and character. Both sexes experience a flood of new emotion and one beats them all… for the first time, both sexes find the other sexually attractive.
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Now with puberty behind us, we are ready in mind and body to become adults. Our early 20s, childhood and puberty are behind us. This is the start of a new phase in our lives…. ADULTHOOD. What happens now is up to us. In our 20s we look and feel better than any other time in our lives. We are in our prime both outside and in. Trillions of cells make up our organs and tissues. Over time, these get damage but new cells grow and divide to replace the old ones. Our body replaces entire organs. So it is no wonder that we feel good. Essentially, every 10 years we get a brand new body. Some tissues regenerate even faster like our hair and nails which require a quick trip to the salon every so often. Hairs are made from modified dead skin cells. Each hair grows from a follicle embedded in the skin. The modified cells grow here then die as new cells push them upward. The column of dead skin cells is the hair. Each person grows an incredible 7 miles of hair every year. Our hair grows whether we want it or not. But other parts of our body are partially under our control. Choices we make now like exercising affect us for the rest of our lives. It has an effect throughout the body. It is helping cells and organs stay in good condition. Our muscles are also building. Muscles are made from bundles of fibers. A good workout rips these fibers apart but our cells repair the damage by adding extra materials. The muscle grows back, bigger and stronger through choices we make. Unfortunately, some choices are less beneficial. Some exposes to damage that even our youthful cells cannot repair. Parties are just a part of our lives. We all know smoke can damage the lungs. But smoke is not the only hazard here. Our hearing is under threat too from loud noise. The problem is deep inside the ear. The fragile sensory hairs in the cochlea or stereo cilla turn sound into nerve impulses. Loud noise destroys these irreplaceable cells. The hairs that respond to high frequency are most affected. High pitched sounds shake their foundations more violently. The effect is too small to notice but frequency range of our hearing is already shrinking. Another source of damage is alcohol. As we absorb alcohol into our blood stream, it affects both our organs and state of mind. It raises our blood pressure and makes our heart beat irregular. We loss coordination. These symptoms are consequence of chemical reactions in the brain especially in the cerebellum. Cerebellum controls coordination and balance. When we drink, alcohol affects cerebellum’s brain cells. Some synapses accept the signal more frequently. Others become totally blocked. The more we drink, the more the extreme the effect. It may feel good now but there will be a price to pay later.
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After a party, time passes and we get to know our limits. Now, new challenges are on the horizon to find love and have children of our own. Our late 20s, childhood is a distant memory but not the thrill of our first kiss. That was pure lust. Now, it is time for something new. It is time to fall in love. Many of us meet our future partners at work. We may think the attraction is social or physical, but a lot of it is biological. Looks are not everything. Attraction is also about smell. Inside the nose, olfactory nerves do more than detect smells. They also detect chemicals we cannot smell, the pheromones. Pheromones are hormonal messages we release in our sweat. They carry information about our genetic health and our ability to resist diseases. Our brains use these signals to help choose a partner with the best possible genes for our children. Love is more than just an emotion. It is all about chemistry. We release adrenalin into the blood. Our heart pounds. We cannot sleep. When that happens, another hormone comes into play. The brain floods with dopamine, the feel-good hormone. It is as potent as cocaine. Makes us euphoric and it is addictive. It leaves us wanting more. We start thinking about commitment and eventually marriage. Love, both chemical and emotional, wins the day. It is a relationship we hope will last a lifetime and the process of long term bonding is chemical. Sex is not just about pro-creation or recreation. It chemically strengthens the bond between us. Both partners’ pituitary glands pump the blood full of substance called oxytocin. It is sometimes called the bonding hormone. It is the very same hormone that bonds us to our mothers as a new born. Some anthropologists believe that oxytocin could be evolution’s way of creating a bond that strong enough to endure the trial of parenthood. And the time of parenthood is now. The man releases sperms. The goal is to find the egg. An egg ripens and bursts from the woman’s ovaries, the largest cell in the human (female) body. It passes in the fallopian tube and ready for fertilization. Sperms are the smallest cell in the human (male) body. They have a long journey ahead of them. First, they have to survive the hostile environment of the vagina. Its secretions are acidic to prevent bacterial infections but also kill sperms. Ejaculation releases almost 300 million sperms but only thousands will make it as far as the cervix. The surviving sperms swim into the uterus and fallopian tube. Muscular contractions in the walls of the fallopian tube help guide
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the sperm toward the egg. Only a few hundred make it this far. Only 1 will succeed in fertilizing the egg. This is truly a survival of the fittest. Ten hours later, the strongest of 300 million sperms is the one to pass on its genes. Over the next 40 weeks, a single cell will develop into a perfectly formed baby. Often the first symptom is morning sickness. No one knows for sure what causes the nausea. One theory is that it protects the fetus from toxins in food which could harm its organs during this critical phase of development. Another theory is that nausea is the side effect of the mother’s immune system as it weakens to avoid attacking the developing embryo. The fetus is effectively a parasite. It saps the mother’s energy as it draws what it need from her body. It has its own life-support system, the placenta. Here, the mother’s blood passes nutrients across a membrane into the fetal blood. With this constant supply of nourishment, the fetus grows over 10 ounces in its first 10 weeks. The uterus expands to 1000 times its normal size just to hold it. That extra space must come from somewhere. So the mother’s body rearranges itself internally. In a pregnant woman, the organs get squeezed and some are pushed up into her chest. Not only are the organs squeezed, the lung and heart work harder than ever before. To make space, muscles and tendons in the spine relax and curve out of its normal shape. The stomach is also compressed and rotated to 45 degrees. It can only hold small amount of food and drinks and still the growing baby demands more. After 9 months, it is time to give birth. And pushing a 7-pound baby can be quite a challenge. Soften tendons allow the pelvis to open up the growth canal. SMA- –
