人体内旅行前两节字幕

人体内旅行第一节：00:00:00 – 00:11:27The incredible journey of life, from birth through infancy, childhood, puberty, adulthood, and the slow maturity to old age. This is the story of our lives. From the unique perspective, deep inside how body is working. This is the journey of a human life from the outside in.A fetus develops in the womb. It's 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 billions of perfectly functioning cells. These cells are the building blocks of our bodies. They make us what we are. A hundred thousand billion cells all working in harmony. Inside every cell is the same extraordinary engine, the machine that tells each cell how to grow, and what functions to perform. DNA is unique to every person, a chemical blueprint of instructions that creates each new life.This baby is ready to enter the world. A new born person who's journey is about to begin. The journey starts with the challenge --- breathe or die. These lungs have never breathed before. They are still full of amniotic fluid that protected them for 9 long months. The new-born is in danger of drowning. Then, the body kicks into survival mode. The adrenal glands, right above the kidneys, send adrenalin surging around the body. It shocks the lungs into live. Muscles we need to breathe suddenly start to spasm. And we take our first breath. It's the most important breath of our lives - the first of 700 million. Our lungs will pump air every single second as long as we live. Air rushes down the wind pipe, down thousands of branching tubes, and into nearly 30 million tiny air sacks the alveoli. These air sacks pull oxygen into our blood, and pump out the carbon dioxide we exhale with every breath and they do it non-stop for 80 years.At the moment of birth, everything changes. The physical link between mother and baby is broken for the first time. The first hour brings rapid change. All the baby's organs have to adapt to life outside the womb. It's a challenging and risky time. At this age, the heart is no bigger than a walnut. It's been pumping in the womb for 8 months. But now it has flaws that could be fatal. Two holes, one in aorta and one in the heart. In the womb, they diverted blood away from our inactive lungs. Now that we need the lungs, the holes seal shut. The heart is working normally, pumping blood through tens of thousands of miles of blood vessels. Other systems are also gearing up. The digestive track is ready to clear itself out to make room for its first meal. The bowels are full of digested amniotic fluid and dead cells, a sticky green black tar-like material called Meconium. It's corrosive stuff. If it ends up in the babies’ lungs during labor, it can attack the delicate lining. But here in the gut, Meconium is harmless. The digestive track flushes it out within days.As time passes, more sophisticated systems starts to kick-in. Our next challenge is the cold. It was 100 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 ofour brains. When an adult is too cold or hot, this area sends out instructions for ourselves to produce more or less energy. It's called the Hypothalamus. And like all our other organs at this age, it's still immature. The brain is under pressure, making 100 trillion calculations per second just to keep our bodies functioning. But it's still learning how. And now we are in danger of Hyperthermia. An inferred camera shows the struggle to keep warm as we lose precious body heat. The yellow areas show where we lose the most. Luckily we are prepared. A layer of special tissue around our blood vessels and vital organs actively generates heat. It's fat. But this isn’t regular fat. It's brown fat, a specialized type usually found in hibernating animals. It's packed with special heat-generating cells. Eventually, most of this fat will melt away as the Hypothalamus matures, and the liver and 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. Feeding is a reflex. Normally, we have no more control over sucking than the urge to breathe. This is milk on its first journey down the Esophagus to the stomach. Mother's milk is much more than the ultimate super-food. It also protects us from hidden danger. Outside the womb, bacteria are everywhere, invisible and potentially deadly. Our day-old skin is under constant attack. There are 10 times more bacteria than human cells in and on our bodies. Our immune systems aren't developed yet. So we can't 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 attacking us. Her immune system creates antibodies. Then she delivers those antibodies back to us, in her milk. Until our own immune system developed, she will keep us save.第二节：00:11:28 – 00:24:30It's been 4 weeks since birth. The baby has drunk nearly 30 pints of milk. And it has put on 2 pounds – a quarter of its body weight. It's time for its first trip outside.1 MonthEven a visit to the grocery store can overload the senses. It's 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 signal 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 ear drum. On the other side of the ear drum, these tiny bones - the Ossicles (听小骨) - vibrate in response. They are the smallest bones in the body, but without them, we will never hear a thing. They use leverage(杠杆) to amplify the vibrations, hitting the ear drum 22 times. The amplified vibrations now enter the inner ear, or Cochlea(耳蜗). It's lined with delicate hairs. When vibrations pass through, the hairsvibrate. At the base are the fragile hairs for high frequency sounds. At the top, low frequency hairs. Each one, 200 times thinner than our 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.The story is different for eye sight. We are born with very underdeveloped vision. Even at one month, the world is blurred, and mostly black and white. Every aspect of our vision is rudimentary. The eye muscles are immature, keeping us from pointing your eyes where we want to. Inside the eye, the lens muscles still can't focus, and the lens flips the image it receives. All through life, we see the world upside down. The picture only gets reoriented in our brains. Right now, the picture is on the Retina(视网膜) - The screen at the back of the eye. The Retina has two types 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 travel along 2 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. That's changing fast. At 2 months we can distinguish colors and shapes. At 4 months, we can identify our mother's face. By 8 months, we have 20/20 vision. (If you have 20/20 vision, you can see clearly at 20 feet what should normally be seen at that distance.)Along with our perfect eye sight, comes a grow spirt. We start packing on pounds. We add 1/4 to our body weight every month. After 3 month, it slows down. Lucky for us. If we kept growing that fast, we weight 150 tons by age 4 - the same as a blue whale.8 MonthAt 8 month, all our senses work. We are beginning to explore the world. And the sense we use most is touch. Touch something too hot and temperature sensors in the skin send nerve signals raising up the arm, up to spinal core 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 sensoring nerve receptors all over our skin, but some areas are more sensitive than others. The hands, face and mouth. There are 9000 sensory receptors on the tongue alone, which is why babies use their mouth to exploreBut there is another reason for all the annoying. Something painful is happening inside the baby's mouth. Her first teeth are coming through. Milk teeth form deep in our gums while we were still in the womb. Now, one by one, they burst through. It's painful, but it's progress. At 8 months into life's 80-year journey. The sensors are operating at full capacity. Every sensation is a new surprise.And with her new teeth, she can take on more solid foods. Digestion starts in the mouth, teeth grind up the food, then special 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'll pass from the stomach into the coils of the small intestine before finally passing into the large intestine. Waves of contracting muscle keep the food moving - A process called Peristalsis(蠕动). This contractions are so powerful, we can even eat upside down. For the first time, a new camera shows a high definition view of how food travels through our bodies and into our stomachs. Food enters the stomach through a hole at the top. The stomach is a bag of muscle that churns, squashes and squeezes food into liquid.At the same time, acids brake the food down. The stomach walls protect themselves with the lining of mucous. Without it, the acids could digest parts of stomach itself, causing Stomach Ulcers(溃疡). About an hour later, the stomach squeezes the broken down food out through a tiny hole called the Pyloric Sphincter(幽门括约肌). The food enters the small intestine. An 11 foot coil of tube where we absorb most of the nutrients. The interior wall of small intestine is lined with millions of microscopic projections called Villi(绒毛). These 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 lever brakes down the fat into tiny droplets. Smaller droplets are easier for the intestine to absorb. After 1 hour and half. The small intestine has absorbed most of the nutrients from the food. It's time for what remains to move on. It enters the large intestine through this - the Ileocecal Sphincter(回盲括约肌), a valve that keeps our food from going back where it came from. What's left is a mix 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 isn't because of an infection. We actually need them. They produce enzymes that brake down complex carbohydrates in our food - carbohydrates we couldn't otherwise digest. Finally, after about 12 hours, we expel what's left of our first meal.。