Transcription
It is riddled with holes, yet contains 15 gallons of water and a pint of hydrochloric acid. It has more protein than 70 pounds of peanuts. It has enough carbon to fill a thousand pencils and enough phosphorus for 3,000 match heads. What sounds like a collection of chemicals in a leaky bag is the most complex structure on our planet: the human body. So [Music] hey, 400,000 humans are born every day. [Music] The one thing we all have in common is the amazing machine we all inhabit: the human body.
In the course of its life, it will breathe 10 million balloons worth of air; it will process 30 tons of food; and it will secrete 17 gallons of tears. But humans rarely stop to think about the amazing technology behind even the most mundane action. At the very center of the body, for example, is an ingenious structure. It is incredibly strong, yet it is ultra-light, so that we can move around freely. The skeleton is made up of 206 rigid bones. It is a framework that keeps the body upright and forms a protective cage around delicate inner organs.
The most vulnerable organ in the body gets special attention. The brain is shielded by 22 bones fused together to form a natural crash helmet. [Music] But the strongest bones in the skeleton work the hardest. As the body lands from an energetic leap, the thigh bones experience an impact of half a ton—a force that would shatter granite. Thigh bones are engineered to survive this kind of treatment. [Music] The ends of the bone have a honeycomb structure consisting of struts and arches. These direct the forces of impact into the stronger, more compact middle section. It's this honeycomb structure that makes bone tough yet light. [Music]
This example of nature's ingenuity inspired an engineer working in Paris in the late 1800s. [Music] He wanted to build the tallest structure in the world. The strongest material available was iron, but he knew that if he used too much, the structure would collapse under its own weight. Following the blueprint of the thigh bone, the engineer used the iron only where it made the structure stronger. [Music] His name was Gustave Eiffel, and his tower became an icon. [Music] The iron girders in the Eiffel Tower, like the struts and arches in a thigh bone, direct all forces acting on the tower into its strongest parts: the legs. [Music] But unlike the Eiffel Tower, bones are not rooted to the spot. [Music] They are constantly on the move and have to cope with all kinds of stresses and strains. [Music]
Any impact on bone triggers an amazing reaction. The shock mobilizes an army of microscopic bone-building machines where stress occurs. These cells excrete a layer of liquid bone; this hardens to strengthen the structure. Areas without stress do not need to be so strong; here bone-destroying cells use hydrochloric acid to dissolve superfluous bone. Like a team of sculptors, the bone cells constantly remodel the skeleton to make it strong where it has to be and light where it can afford to be. But it's not just the bones of athletes that undergo perpetual change; it happens to all of us. We take around five million steps a year, and each one does its share to shape our bones. [Music] To every action there is a reaction: exercise strengthens the skeleton; driving a car weakens it. [Music] All through their lives, humans thus sculpt their own unique skeletons. [Music] Bone cells work so hard that every person gets a completely overhauled skeleton every 10 years. [Music] So whatever age you are, your skeleton can never be more than 10 years old.
The biggest organ in the body weighs in at about nine pounds and covers an area of about 20 square feet. Rubbing it makes it flake off, filling our houses with dust. [Music] It's the skin. The part of skin you can see is made up of dead cells. These overlap like tightly packed roof tiles, making the body waterproof. [Music] [Music] Skin stops precious water from escaping and harmful chemicals from entering. [Music] While it is a formidable barrier, skin has to be flexible—sometimes extremely so. [Music] Pregnant women produce a hormone that allows their skin to stretch to twice its size. [Music] But skin is not just an inert coating; it is an active organ with a vital function. Skin keeps the body cool. This heat-sensitive camera shows, in red and yellow, the hottest areas on a body in action. During heavy exercise, muscles generate enough heat to boil several cups of coffee. This heat would easily damage the internal organs unless the body did something about it. Just below the skin surface are three million temperature control units; these are the sweat glands, each a coiled tube four feet long, loaded with liquid. As the body heats up, the tube contracts, squeezing a droplet of sweat out onto the skin. As the sweat evaporates, it draws heat from the skin and cools the body. A body working flat out can expel two pints of sweat per hour.
For an organ so packed with such finely tuned technology, skin is surprisingly robust. Woven beneath the surface of skin is a mesh of tough collagen fibers. A strand of collagen is stronger than a steel wire of the same dimensions. If skin lacks collagen, it is weak. This hardly matters unless it is pushed to its limit. Four years ago, Billy Schwer lost his bid for the lightweight championship of the world. [Music] His skin let him down. The part was going really well, actually, but unfortunately, I got two really bad cuts when I reach. Unfortunately, the referee had to stop the fight at the end of the eighth round. Losing the championship because of cut eyes is a—it's a terrible way to lose a championship, really, but um, that's boxing. Billy has tried to overcome his skin's lack of collagen by enriching his diet with collagen-building supplements and undergoing laser treatments to make his skin stronger. It appears to be working. Philly has not been cut in his last four fights, but his skin is about to face its toughest test: world champion Stevie Johnston. [Music] I really do believe that this is my time now, and fingers crossed on the night it’d be okay for me. [Music] [Applause] In the third round, Billy was cut. He fought on, only to suffer further cuts to his eyes and nose, but these were not serious enough to stop the fight. [Music] There really went the full distance but lost to the champion on points. [Music]
It's hard to imagine, but given time, Billy's cuts will heal. This is what makes skin truly amazing. When skin is cut, hundreds of blood vessels are severed, flooding the wound with blood. This carries the body's healing kit. Small cells called platelets stick to each other and form temporary plugs that slow down the bleeding. Threads of protein form a tight mesh, trapping blood cells. This becomes the scab. The scab contracts, pulling the edges of the wound closer together. Eventually, the scab falls off, leaving behind a strip of new skin. [Music] This is Billy three months after the fight. [Music]
The human body seems to break all the rules of engineering. It is top-heavy, yet balances on just a few square inches of flesh and bone. [Music] This is why we have developed a clever system to keep us upright. [Music] But we have to learn how to use it. Once the basics are mastered, we can push our balance organs to the edge as we bend our limbs. Microscopic strain gauges measure the tension in the muscles to make sure we do not lean too far. The eyes lock on to familiar references like the horizon, the judge which way the body is leaning. But the most important information for balance control comes from deep inside the skull. At the very center of the inner ear are two tiny sack-like organs. [Music] Each sack contains a patch of jelly covered with thousands of tiny crystals. As the head tilts, gravity pulls these crystals toward the ground. The slightest movement of these crystals stimulates nerve cells embedded in the jelly to fire off electrical messages. This tells the brain which way our head is tilting. These organs are so sensitive that we can detect a change in the angle of the head by as little as a few widths of a hair. The one limitation of the balance system is that it needs gravity to work. We have main engine start: four, three, two, one. We have booster ignition and liftoff. When we venture into space, we start to experience problems. Vertical and horizontal reference points are not where the eyes expect them to be. The strain gauges in muscles experience less resistance than they are used to, and without gravity to pull on them, the crystals in the inner ear stop sending accurate information. As a result, the balance system goes awry. It is an experience all too familiar for Dr. Ellen Baker, a medic on three space shuttle missions. Until you're really weightless, you just don't know what it's going to be like. You don't know how your body's going to react; you don't know how you're going to adjust when your world is turned in any number of directions. But it's [Applause] [Music] and I think as the mission goes on, you find your feet are facing the floor less and less often. It looks okay.
Astronauts eventually adapt to their balance sensors giving them confusing and unfamiliar information. After a short time in space, the human body actually forgets how to deal with gravity and instead learns how to balance and move around without it. That is a problem when astronauts returned to Earth. Touchdown: one flawless mission completed. I actually had a harder time coming back than I did going. Normal sensations of moving your head don't feel so normal, for example. Every time I would turn my head back and forth, I'd feel like my body was translating back and forth, and some people have that same sensation when they pitch their head forward; they feel like they're tumbling. And it probably took me a good six or seven hours to feel like I could walk without making myself sick. I would say virtually everybody has those sorts of problems to a different degree. On returning, astronauts feel a sensation not unlike seasickness when they return to gravity because the signals from their reawakened ear crystals do not match with what their eyes are telling them. This confuses them and results in disorientation. Every astronaut has some disturbance of balance or gait after return from flight. If you watch them walk around under the shuttle, for instance, as they try to walk around corners, they take it too short and clip their elbow or their knee on the corner. There's a funny illusion that many of them report: if they walk upstairs right after space flight, it feels not like they're walking up the stairs but often like they're pushing the stairs down.
After landing, astronauts are tested for balance in a computer-controlled booth. This test—please keep your eyes open and try to maintain an upright stance. Here we go, Bill Pulaski. Can move the base plates and the visuals around to assess the performance of each of the balance sensors. You feel like you know where upright is? I think so. I think I'm tilting back right now, and now I feel like I'm about to fall forward. He has found that the inner ear organ is impaired the most. Okay, wow. You all right? Yeah, I'm fine. [Music] The longer a human spends in weightlessness, the longer it takes the body to readapt to gravity. It can take weeks for an astronaut to get over the nausea and disorientation. This is a simulation of NASA's latest brainchild: a manned mission to Mars. As soon as they touch down, the crew would have to cope with a planet's gravity, which is only half that of Earth, but enough to cause problems. The kinds of disturbances that they have on landing um, put them at a higher risk of falling, and if one were to fall and and hurt oneself on the Martian surface, then it could disrupt the mission, or it could hurt the person for a long period of time. It could be some dire consequences with the nearest hospital six months away. Any injury would be catastrophic. NASA wants to solve the balance problem by reminding astronauts what gravity feels like. They plan to dose them with artificial gravity by spinning them in a centrifuge for short periods during the flight. As soon as they land, they would be ready to start work without the risk of disorientation. When we provide this therapy, then when they arrived at the Martian surface, they'd probably be able to get up and just go rather than have to wait for two to four weeks before they could adapt to that environment. [Music] [Music]
Perhaps the most sophisticated instrument in nature is something we take for granted: the human hand. We only consider it when it needs maintenance, but the hand is a remarkable piece of mechanical engineering. It contains more moving parts controlled by more muscles than any other structure in the body. [Music] This is why the hand can perform such an enormous variety of movements. It is capable of both brute force [Music] and incredible finesse. But the hand has not always been so [Music] versatile. At the University of Arizona, physical anthropologist Dr. Mary Marsky is investigating the evolution of the hand. She believes that it was molded by millions of years of practice. Three and a half million years ago, humans learned to stand upright, freeing up their front paws to learn new skills. This is Lucy, our oldest known upright ancestor. The area in Ethiopia where she was discovered was strewn with stones that she may have used as crude tools. All that is now left of Lucy are a few fossilized bones. So in order to find out whether Lucy's hands were equipped to make tools, Dr. Marsky had to do some detective work. If you could just go through the motions, see if I have it all in the picture. [Music] As an archaeologist goes through the motions required to make a simple prehistoric cutting tool, [Music] electrodes fixed to his hand measure which muscles are active. This allows Dr. Marsky to pinpoint which muscles Lucy would have required to make such tools. Well, Lucy would have had muscles very similar to ours, probably the same full complement of muscles that we have, and the muscles would have had to have enough leverage so that she could hold on to objects tightly, because in much of tool making you have to be able to hold the tool with one hand, hit it with another, and prevent them from flipping out of the hand, and the working surface has to be exposed; otherwise you smash your fingers. Apes can hold things very tightly and grasp things very tightly with their fingers, but it covers up the working surface, so the muscles had to be built a little bit differently. By taking close-up photographs of Lucy's finger bones, Dr. Marsky is able to reconstruct a three-dimensional image of the joint surfaces. From the shape and curvature that was revealed, she is able to judge the amount of movement Lucy's fingers may have had. Well, Lucy doesn't seem to have had so much of a range of movement for her little finger, especially in the palm of the hand coming toward the thumb. All right, we're going to do clubbing, and this might have had an effect on her ability to get a good grasp of cylindrical objects like bones that she might have used for pounding or clubbing. On the other hand, she had some features which she shared exclusively with modern humans, and these features provide a little give at the base of the index finger, allowing it to be pulled over toward the thumb, so that we think that she would have had the ability for a good, well-controlled three-jaw chuck grip of something like stones that she could have thrown. [Music]
Throwing objects with speed and precision may have been the one thing that gave early humans the edge over other animals. This ability meant that any predator would have thought twice about attacking Lucy or her kind. This gave humans the freedom to perfect their manual skills and allowed the hand to evolve. [Music] Engineers at NASA have achieved in five years what took nature millions of years to accomplish: they have built a robotic hand that can do almost everything the human hand can do. The NASA hand will one day be part of a robotic astronaut that will perform sophisticated maintenance tasks outside spacecraft. It takes a bank of computers merely to control the mechanical components of the hand, but it needs an even more sophisticated piece of hardware to guide it by remote control: a human brain. There are an infinite number of possible situations that the hand needs to cope with. This enormous task leaves even the most powerful computers stranded. We actually spend most of our early childhood teaching our brains how to control our hands. Just to open a tin can, the brain has to send millions of nerve signals to the hands every second while it simultaneously coordinates a multitude of other bodily functions. The brain can do this because it processes information in a unique way: it splits the workload among its 100 billion cells, each communicating with 10,000 other cells via a network of electrical connections. [Music] To get an idea of the scale of this system, imagine making a phone call. Now imagine making a phone call to everyone you know. Now imagine every citizen in a city as big as New York calling every single name listed in the telephone directory. What if the same thing was happening in every single city in the world? [Music] How long would it take? How many connections would that amount to? [Music] It's getting close to the number of connections the brain can activate per second. It makes them quietly. But the brain is not confined to the 85 cubic inches of space inside the skull. The brain is able to reach out and experience the world through the senses. The sense of touch calls on five million powerful sensors sprouting from the skin. Each hair has a nerve at its root so sensitive it is sparked by the slightest pressure; a mote of dust is all it takes. The sense of hearing relies on specially shaped pieces of cartilage attached to the sides of the head. [Music] The ridges and hollows of the ear vibrate at different frequencies according to the location of the sound source. This helps us determine where a sound comes from. The surface of the tongue is dotted with 9,000 chemical detectors: these taste buds require just a few molecules of a substance to detect whether it's bitter, salty, sour, or sweet. The radar net of the senses even extends far beyond the body itself. We can distinguish up to 10,000 different smells, which language is not equipped to describe. How do you describe the smell of a sunny afternoon or a newborn baby? [Music] We are literally bathed in smells as odor molecules are floating around us all the time. Every breath draws millions of these molecules up into the nostril. The stream of molecules winds its way right up to a small patch at the top of the nose. This area is packed with millions of nerve cells that can register smells. The odor molecules dissolve in the sticky mucus surrounding the tips of these cells. Each nerve ending is studded with tiny receptors that will react to only one specific kind of molecule. Once the odor molecules lock into the correct receptor, they trigger electrical impulses. [Music] These signals feed straight into the brain area that controls emotion and memory. That explains why smells are so good at bringing back memories and influencing our mood. The conscious part of the brain eventually translates all the electric signals from the nose into what we perceive as a smell. So ultimately, we smell with our brains.
The brain plays an equally important role in sight. More space in the brain is devoted to vision than to all the other senses put together. A picture hitting the retina triggers a wave of electrical activity which travels through the optic nerve to the brain. Within fractions of a second, the brain neatly divides this electric storm into separate chunks of information: for color, edge, form, movement, or depth. Eventually, the brain rebuilds the separate elements into a picture we can understand. Unless you are blind, neurobiologist John Cronley Dylan is trying to do something that sounds like a miracle: make blind people see. His inspiration came from an unlikely source. It was found quite a long time ago that if you'd cut an optic nerve of a goldfish and you waited a few months, it would regrow. The million or so nerve fibers that had been severed would home back into the brain and connect up within the brain, and the question is why can the goldfish do it and we can't do it. There are a lot of laboratories all over the world that are looking at this problem, and in fact, it looks as if we even we may be able to stimulate the growth, and it's very encouraging, but it's still a long way off. Professor Cronley Dylan's aim is to come up with an alternative system. He believes that the part of the brain that is normally used for vision can be retrained to adapt to extra auditory input. [Music] The boundaries between the different senses may not be as sharply demarcated as we've always thought to be the case. There are certain visual areas of the brain that receive input from the auditory system. At the University of Manchester, Cronley Dylan is attempting to teach his blind subjects to recognize pictures by their sound, like this fish [Music] or this horse. He gives horizontal lines one sound, the pitch depending on its height; verticals another; diagonals another. [Music] Then if the picture is simplified into a line drawing, it has a characteristic sound. [Music] The picture can be split into simple sections or played as a whole. Right, well, I've got a number of uh images of scenes taken in this area, but what I'm going to do is to let you listen to the whole sound signature for the whole scene. Right, you've heard what I played, the whole thing. Can you tell me what you think it is? I think the the major part of the picture is a big building because you can hear all those verticals, and they're the signatures for many windows. That's right. The other thing on the left and the right of it must be in the foreground because they seem even bigger in some senses, so I guess that the tree must be on the right must be uh in the front of the picture on the left-hand side. Uh, could it possibly be the outline of another building perhaps? Yes, that's right. Professor Cronley Dylan's ultimate aim is that the subject would carry a camera attached to a computer which would simplify scenes and provide the relevant musical signature, acting as an aid like the guide dog or the cane. It's a way of touching the world with you. This is what our eyes do: they're touching the world for you at the distance. Now it's true that touch does that, but with a cane you're limited to within arm's lengths. We see it as providing information which is not at the present available to a blind person.
The brain is able to adapt and learn new skills because, unlike the hardware inside a computer, the brain is not set in stone. [Music] It is of an almost fluid nature. [Music] Think of the brain as a pond, and any kind of experience has a pebble hitting the water. Waves of electrical activities spread out through the brain like ripples on the pond. Different ripples merge and form new patterns. [Music] The surface of the pond changes all the time, just like the brain, which is constantly rewiring itself. Every thought, every emotion can create a new connection or strengthen an existing one. This is how we learn. [Music] Behind all of this activity is an army of microscopic machines responsible not only for the brain's actions but for every process within the [Music] body. Humans are made up of about 70 million million cells. [Music] Boyce Rensburger, science writer turned biologist, has become obsessed with investigating the wonders of the cell. The entire human body is made out of cells, or the things that cells have made, such as bone. Skin is made of cells; your heart is made of cells; the muscles that operate the the body so that you can move, these things are all made of cells, including the brain itself, which sends electrical signals around from one cell to the other so that we can think. All these different kinds of cells work fundamentally the same way. When you look inside the cell, you see the same kinds of structures. Inside a single cell there are hundreds of microscopic power stations, protein factories, recycling plants, and transport highways. [Music] The nucleus is the control center of the cell; it contains DNA, the blueprint of life that tells a cell how to assemble its infrastructure. The outer wall of the cell allows it to take in the raw materials it needs to stay alive. Cells trap these materials from the outside and package them into tiny cargo bubbles called vesicles. The bubble hitches a ride on a motor no bigger than a molecule which latches on to one of the miniature monorail tracks that form the cell's transport network. [Music] Usually the bubbles reach their destinations within seconds, but in the biggest cells, which stretch from the spine to the toe, the journey can take four days. Each bubble carries a code, a chemical address label that guides it to a particular location. When it reaches its target, perhaps a lysosome, one of the cell's many recycling plants, it hops off the track and empties its cargo. The job.
Of the recycling plant is to break down the delivered raw materials into smaller building blocks, which the cell uses to grow. [Music] The instructions that are in the cells, starting in embryonic development, tell each cell how to change to take on a new function. Also, the cells monitor the activities going on; if there's a wound, the cells can sense that, and they will send out the message to other cells to come and repair the damage. So all of this keeps the whole body on a kind of an even keel. [Music]
Sometimes, though, our cells don't behave as they're supposed to, and they are unable to repair damage to the body. Ten years ago, outdoors enthusiast Sean Sarason cut his leg. Unfortunately, the wound was inflamed for such a long period of time that Sean's skin cells were not able to grow and heal the wound. "It's quite disturbing when you get a wound area of your skin that's not healing like every other part of your body does," he says. "You cut your hand, you cut your face, everything grows back when the cells realize that there's been damage done, but in my leg that wasn't happening." And so they tried a skin graft, which failed; they tried another skin graft, which failed. And so that's why we needed to take some different measures.
Sean is one of 3,000 people who have received a revolutionary treatment: a graft of artificial skin. [Music] Scientists from biotech companies have harnessed the power of the cell to grow tissue from scratch. The best cells to use are those from the circumcised foreskins of newborn babies, because they multiply rapidly. [Music] The cells from just one foreskin can grow a football field's worth of skin. [Music]
This is a sample of the latest generation of factory-grown skin called Apligraf. It has neither hair nor sweat glands, but it is teeming with young, vigorous cells. [Music] "Legs looking good here," says the doctor. "It's gotten quite a bit smaller, I think, since your last visit here. I'm going to measure it. That now measures 55 millimeters, so it's healed almost by half in the last month, and it must be 80 percent healed from when we originally put on the Apligraf, I would say." [Music] "It's re-taught my skin cells to grow, and when they haven't done that for a long time, it's just been a remarkable process of healing for me."
It seems that cells really are the fundamental building blocks of life. If so, what more can scientists learn about life by studying cells? "Everything we've looked at turns out to be explainable and understandable in terms of chemistry and physics," says one scientist. "So the next question is, what about consciousness? You know, this seems like such a mysterious thing." [Applause] "Can it be explained through entirely natural processes?" Most scientists say yes, of course it can. It's undoubtedly going to be one of the last frontiers in the study of how life works at the most fundamental level. We may get close to it; we may never get close to it. Could it be that our incredible bodies are no more than the result of physics and chemistry? [Music]
Even if one day our very thoughts could be explained in terms of cells and molecules, there is something that lies beyond the realm of science. Quite simply, how we live our lives, our experiences and memories, really make us who we are: unique inhabitants of nature's most complex machine—the human body. [Music] You