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Heart, Lungs, Kidney, Stomach, Liver, Brain. Your heart is really a muscle. It's located a little to the left of the middle of your chest, and it's about the size of your fist. There are lots of muscles all over your body - in your arms, in your legs, in your back, even in your behind. But this muscle is special because of what it does - the heart sends blood around your body. The blood provides your body with the oxygen and nutrients it needs. It also carries away the waste that your body has to get rid of. Your heart is sort of like a pump, or two pumps in one. The right side of your heart receives blood from the body and pumps it to the lungs. The left side of the heart does the exact opposite: it receives blood from the lungs and pumps it out to the body. By the time you're grown up, your heart will be beating (pumping) about 70 times a minute.
The movement of the blood through the heart and around the body is called circulation, and your heart is really good at it. It's so good at it that it only takes about 20 seconds to pump blood to every cell in your body. That's less time than you need to sing "Take Me Out to the Ballgame"! Your body needs this steady supply of fresh blood to keep it working right. It also needs the blood to get rid of waste that would make your body sick if it stuck around. The left side of your heart sends fresh, clean blood to the body. This blood has lots of oxygen in it, and the oxygen is what makes your cells happy. The body takes the oxygen out of the blood and uses it in your body's cells. The cells say thanks by using the oxygen, making carbon dioxide and other stuff it needs to get rid of, and dumping the carbon dioxide and wastes back into the blood to be carried away. The blood has done the first part of its job by delivering the oxygen to the cells, and now it's time for it to pick up the trash (the carbon dioxide and other waste). Each time the blood circulates from the heart out to the body, about 20% (one fifth) of it goes through the kidneys where some of the waste is filtered out, and then the blood heads back to the heart. The right side of the heart is ready for the hand-off: it takes the stale, used-up blood to the lungs for a little freshening up. The carbon dioxide leaves the blood by getting breathed out by the lungs, and the new oxygen gets breathed in. Now this new blood has got the oxygen it needs to go back to the left side of the heart and start all over. And remember, it all happens in less than half a minute!
When you go for a checkup, your doctor uses a stethoscope to listen carefully to your heart. A healthy heart makes a "lub-dub" sound with each beat. This sound comes from the valves shutting on the blood inside the heart. The first sound (the "lub") happens when the blood hits the mitral and tricuspid valves between the atria and ventricles. The next sound (the "dub") happens when the blood hits the aortic and pulmonic valves that close up as the heart relaxes to fill with blood for the next beat. Next time you go to the doctor, ask if you can listen to the "lub-dub," too.
Most kids are born with a healthy heart and it's important to keep yours in good shape. Here are some things that you can do to help keep your heart happy: Remember that your heart is a muscle. Just like you need to exercise your leg and arm muscles, you need to exercise your heart, too. Regular exercise is a great way to keep your heart in shape. At least 15 to 20 minutes of exercise each day will give your heart the workout it needs to be the strongest muscle it can be. Eating a variety of healthy foods is great for your heart. Avoiding a lot of fatty foods will keep your heart happy, too. Stay away from smoking! Smoking is bad for every part
of your body, and especially your heart. Your heart and blood vessels
hate cigarettes, because smoking makes their jobs much harder.
Your lungs are protected by your rib cage, which is made up of 12 sets of ribs. These ribs are connected to your spine in your back and go around your lungs to keep them safe. Beneath the lungs is the diaphragm (say: dye-uh-fram), a dome-shaped muscle that works with your lungs to allow you to inhale (breathe in) and exhale (breathe out) air. You can't see your lungs, but it's easy to feel them in action: put your hands on your chest and breathe in very deeply. You will feel your chest getting slightly bigger. Now breathe out the air, and feel your chest return to its regular size. You've just felt the power of your lungs!
At the same time, you inhale air through your mouth or nose, and the air heads down your trachea, or windpipe. On the way down the windpipe, tiny hairs called cilia (say: sill-ee-uh) move gently to keep mucus and dirt out of the lungs. The air then goes through the series of branches in your lungs, through the bronchi and the bronchioles. The air finally ends up in the 600 million alveoli. As these millions of alveoli fill up with air, the lungs get bigger. Remember that experiment where you felt your lungs get larger? Well, you were really feeling the power of those awesome alveoli! It's the alveoli that allow oxygen from the air to pass into your blood. All the cells in the body need oxygen every minute of the day. Oxygen passes through the walls of each alveolus into the tiny capillaries that surround it. The oxygen enters the blood in the tiny capillaries, hitching a ride on red blood cells and traveling through layers of blood veseels to the heart. The heart then sends the oxygenated (filled with oxygen) blood out to all the cells in the body.
The air that you breathe out not only contains wastes and carbon dioxide, but it's warm, too! As air travels through your body, it picks up heat along the way. You can feel this heat by putting your hand in front of your mouth or nose as you breathe out. What is the temperature of the air that comes out of your mouth or nose? With all this movement, you might be wondering why things don't get stuck as the lungs fill and empty! Luckily, your lungs are covered by two really slick special layers called pleural membranes (say: ploo-ral mem-branes). These membranes are separated by a fluid that allows them to slide around easily while you inhale and exhale. Take Care of your Lungs Your lungs are amazing: they allow you to breathe, talk to your friend, shout at a game, sing, laugh, cry, and more! And speaking of a game, your lungs even work with your brain to help you inhale and exhale a larger amount of air at a more rapid rate when you're running a mile - all without you even thinking about it once. Keeping your lungs looking and feeling healthy is a good idea, and the best way to keep your lungs pink and healthy is not to smoke. Smoking isn't good for any part of your body, and your lungs especially hate it. Cigarette smoke damages the cilia in the trachea so they can no longer move to keep dirt and other substances out of the lungs. Your alveoli say, "ouch," too, because the chemicals in cigarette smoke can cause the walls of the delicate alveoli to break down, making it much harder to breathe. Finally, cigarette smoke can damage the cells of the lungs so much that the healthy cells go away, only to be replaced by cancer cells. Lungs are normally tough and strong, but when it comes to cigarettes, they can be hurt easily - and it's often very difficult or impossible to make them better. If you need to work with chemicals in an art or shop class, be sure to wear a protective mask to keep chemical fumes from entering your lungs. You can also show your love for your lungs by exercising! Exercise is good for every part of your body, and especially for your lungs and heart. When you take part in vigorous exercise (like biking, running, or swimming, for example), your lungs require more air to give your cells the extra oxygen they need. As you breathe more deeply and take in more air, your lungs become stronger and better at supplying your body with the air it needs to succeed. Keep your lungs healthy and they will thank you for life!
Kidneys normally come in pairs. If you've ever seen a kidney bean, then you have a pretty good idea what the kidneys look like. Each kidney is about 5 inches long and about 3 inches wide, about the size of a computer mouse. To locate your kidneys, put your hands on your hips, then slide your hands up until you can feel your ribs. Now if you put your thumbs on your back, you will know where your kidneys are. You can't feel them, but they are there. Read on to find out more about the cool kidneys.
First, the blood is carried into the kidneys by the renal artery (things related to the kidneys are called renal). About 400 gallons of recycled blood are pumped through the kidneys every day! Then the waste is collected out of the blood by tiny filters inside the kidneys. These filters are called nephrons, and they are tiny. There are over a million nephrons inside each kidney. The waste that is collected is combined with water to make urine. The urine goes down some tubes to the bladder, a storage bag that holds the urine. When the bladder is about halfway full, your body tells you to go to the bathroom. Then the urine goes from the bladder down another tube and out of your body. The kidneys, the bladder, and their tubes are called the urinary system. Here's a list of all of the parts of the urinary system: the kidneys: filters that take the waste out of the blood
and make urine
Your body gets water when you drink it or when you drink other liquids. You also get water from some foods, like fruits and vegetables. Water leaves your body in several ways. It comes out of your skin when you sweat, out of your mouth when you breathe, and out of your urethra in urine when you go to the bathroom. There is also water in your bowel movement. When you feel thirsty, your brain is telling you to get more fluids to maintain the balance. If you don't have enough fluids in your body, the brain communicates with the kidneys by sending out a hormone that tells the kidneys to hold onto some fluids. When you drink more, the hormone level goes down, and the kidneys let go of more fluids. You might notice that sometimes your urine is darker in color than other times. Remember, urine is made up of water plus the waste that is filtered out of the blood. If you don't take in a lot of fluids (or if you sweat a lot), your urine has less water in it and it appears darker. If you drink lots of fluids, the extra fluid comes out in your urine, and it will be lighter. Kidneys are always busy. Besides filtering the blood and balancing fluids, the kidneys constantly react to hormones that the brain sends them, and they even make some of their own hormones. For example, the kidneys produce a hormone that tells the body to make red blood cells Attached to the end of the esophagus is the stomach, a stretchy "sack" that's shaped like the letter "j." The stomach is like a mixer, churning and mashing together all the small balls of food that came down the esophagus into smaller and smaller pieces. It does this with help from the strong muscles in the walls of the stomach and gastric (say: gas-trick) juices that also come from the stomach's walls. These gastric juices help to break down food and make a sort of liquidy mixture in the stomach. They also help to kill bacteria that might have come along with the food. It takes about 4 hours for the stomach to do this job completely and get the mixture ready for the next part of the digestive tract. So now that pizza and orange are a liquid mixture - not anything like how they looked on your cafeteria tray! If you're like a lot of kids, you may have been unlucky enough in the past to see what this liquid mix looks like: it's what vomit (throw up) is made of. If a person eats food that has lots of bacteria, or if the stomach gets irritated by a virus or other germ, the stomach says, "Hey, this food's not going any further!" So the muscles of the stomach squeeze themselves together to push the food out the way it came - back out through the esophagus and mouth. Luckily, though, the liquid mixture almost always goes the right way. When the stomach's job is done, the muscles work together to push the mixture bit by bit into yet another part of the digestive tract called the small intestine.
But the small intestine can't break down food for its nutrients by itself - it gets help from three other parts of the digestive system. These parts are the pancreas (say: pan-kree-us), the liver, and the gallbladder. They are not part of the digestive tract itself, but they help to make up the whole digestive system. How? By sending different juices to the first part of the small intestine. These juices help to digest food and allow the body to absorb its nutrients. The pancreas makes juices that help the body digest fats and protein. A juice from the liver called bile helps to absorb fats into the bloodstream. And the gallbladder is like a warehouse for this bile, holding onto extra amounts of it for when the body needs it. In the upper part of the small intestine, the liquid food mix combines with the juices from the pancreas and the liver. After all this mixing of juices, the liquid food mix has now become very thin and watery. It moves into the lower part of the small intestine, getting broken down even further. When the mix is almost at the end of its journey through the small intestine (a trip that can take 4 hours from start to finish!), the nutrients from the food can finally pass through the wall of the small intestine and into the blood. So now that pizza and orange can really get used by your body: complex carbohydrates from the pizza crust, vitamin C from the orange, protein from the meatballs, and many other nutrients to keep you healthy. Once the nutrients have entered your blood, the blood takes them to a major checkpoint: the liver. The large intestine is fatter than the small intestine (3 inches to 4 inches around), and it's almost the last stop on the digestive tract. Like the small intestine, it is packed into the body, and if it were stretched out would be about 5 feet long. The large intestine has a tiny tube with a closed end coming off it called the appendix (say: uh-pen-dix). Although the appendix is part of the digestive tract, it doesn't do anything at all. Scientists think that the appendix may have been a useful part of the digestive tract millions of years ago. After almost all of the nutrients have been absorbed from the liquid food mix in the small intestine, there will still be some parts of the pizza and orange that your body can't use. This leftover waste moves into the large intestine to begin its long journey out of your body. On its way, it goes into the colon (say: cole-in), the part of the large intestine where most of the water (and some minerals) that are left in the liquid mix are absorbed into the blood. As the water leaves the mix, the waste that's left gets harder and harder as it keeps moving along, until it becomes a solid. When this solid waste reaches the end of the large intestine, it may have been in your system for several days. The amount of time that the waste spends in the large intestine depends on the kind of food that was eaten and how a person's body works. The large intestine pushes the waste into the rectum (say: reck-tum), the very last stop on the digestive tract. The solid waste stays here until you are ready to go to the bathroom. When you go to the bathroom, you are getting rid of this solid waste by pushing it through the anus (say: ay-nuss). Everything your body needs from the pizza and orange has been removed by the different parts of the digestive system, and what's left is what comes out of your body. The liver is one of your body's bigger organs, sitting on the right side of your body near the digestive tract. In addition to making bile to help with digestion, the liver is the first place that the nutrients from food go. The blood brings them directly there before going anywhere else, and for good reason: the liver processes the nutrients by filtering out any harmful substances or wastes. It turns some of the waste into more bile, which goes to the small intestine to help with digestion or to the gallbladder for storage. The liver even helps figure out how many nutrients will go to the rest of the body, and how many will stay behind in storage! (For example, the liver stores certain vitamins and a type of sugar that your body uses for energy.) Once everything has passed through the liver for inspection, the liver then gives the go-ahead, and the nutrients can be carried in the blood to the rest of the body. How do you remember the way to your friend's house? Why do your eyes blink without you ever thinking about it? Where do dreams come from? Your brain is in charge of these things and a whole lot more. In fact, your brain is the boss of your body. It runs the show by controlling just about everything you do.
The brain is always working. Even when you're sleeping, it's doing all kinds of things. Sleep is like a time-out for your body, so you can feel rested and prepared for the next day. But your brain never sits on the bench! Even as it's telling your body to sleep, parts of your brain are awake, taking control of how you sleep. There are five stages of sleep, and your brain is in charge of each one. In the first stage, as you're drifting off to sleep, your brain tells your heart to beat slower and tells your body to lower its temperature a bit. It also sends messages to your muscles to relax. In the second stage, you're in a light sleep. You might wake up from a noise or touch. But if your dog doesn't jump on the bed or start to bark, you progress to stage three. Now you're in a deep sleep. Your brain tells your blood pressure to go down, and you won't be very sensitive to the temperature of the air around you, either. Then it's time for stage four, the deepest sleep yet. This is the stage where some people sleepwalk or sleeptalk. It's difficult to be awakened from this stage of sleep. The very last stage is called REM sleep. REM stands for rapid eye movement, because even though your muscles are totally relaxed, your eyes move back and forth quickly and your heartbeat increases. This is the stage when you dream. As the night goes on, you repeat stages two, three, four, and REM every 90 minutes - that's about four or five times a night! No wonder the brain is so busy! When you go into REM sleep, your eyes may start to flutter behind your eyelids. This means you're dreaming! Everybody has dreams, but some people can't remember them as well as other people do. What's your brain doing when you're having a dream? Some scientists think that dreams are your brain's way of sorting through what happened during the day. The things that are important get stored in memory, and the rest goes away, like sorting through mail. The good stuff is what gets saved, and the bad junk mail gets thrown out |
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