The role of Alveoli in the respiratory system Home / Training Zone / The Human Body / Respiratory System / Alveoli Alveoli Part of the respiratory system, these tiny alveoli have a key role in the movement of oxygen and carbon dioxide. Role in the respiratory system. The final branches of the respiratory tree, alveoli are where oxygen from the air enters your blood, and carbon dioxide from your body is expelled back into the air. How they work. Air enters the body through the nose or mouth, passes through the larynx, down the trachea, and into our lungs. Once it is in your lungs, air goes through a maze of smaller and smaller bronchial tubes until it reaches clusters of tiny sacs the alveoli. In appearance they are somewhat like bunches of grapes. Size and where they live. These alveoli are tiny, but your lungs are simply packed with them an estimated three hundred million per lung, all required to ensure that your body gets the oxygen it needs. Once it is in your lungs, the blood has to get into your blood. The alveoli are the primary gas exchange units of the lung.

Quite simply, they are the point where the gas-blood barrier is thin enough to permit rapid gas exchange. To get into the blood, oxygen is diffused through the alveolar epithelium, a thin interstitial space, and the capillary endothelium. Role also has to be reversed. That is only half the process of course this process also has to work in reverse in order to allow CO2, a waste product carried by the blood, to be expelled back into the lungs, and thus out of the body when we exhale. Human Respiratory System and Lungs; How They Work Clearing the Air You usually don't even notice it, but twelve to twenty times per minute, day after day, you breathe -- thanks to your body's respiratory system . Your lungs expand and contract, supplying life-sustaining oxygen to your body and removing from it, a waste product called carbon dioxide . The Act of Breathing Breathing starts at the nose and mouth . You inhale air into your nose or mouth , and it travels down the back of your throat and into your windpipe, or trachea . Your trachea then divides into air passages called bronchial tubes.

For your lungs to perform their best, these airways need to be open during inhalation and exhalation and free from inflammation or swelling and excess or abnormal amounts of mucus. As the bronchial tubes pass through the lungs, they divide into smaller air passages called bronchioles. The bronchioles end in tiny balloon-like air sacs called alveoli. Your body has over 300 million alveoli. The alveoli are surrounded by a mesh of tiny blood vessels called capillaries. Here, oxygen from the inhaled air passes through the alveoli walls and into the blood . After absorbing oxygen, the blood leaves the lungs and is carried to your heart . Your heart then pumps it through your body to provide oxygen to the cells of your tissues and organs. As the cells use the oxygen, carbon dioxide is produced and absorbed into the blood. Your blood then carries the carbon dioxide back to your lungs, where it is removed from the body when you exhale. The Diaphragm's Role in Breathing Inhalation and exhalation are the processes by which the body brings in oxygen and expels carbon dioxide. The breathing process is aided by a large dome-shaped muscle under the lungs called the diaphragm.

When you breathe in, the diaphragm contracts downward, creating a vacuum that causes a rush of fresh air into the lungs. The opposite occurs with exhalation, where the diaphragm relaxes upwards, pushing on the lungs, allowing them to deflate. Clearing the Air The respiratory system has built-in methods to prevent harmful substances in the air from entering the lungs. Hairs in your nose help filter out large particles. Microscopic hairs, called cilia, are found along your air passages and move in a sweeping motion to keep the air passages clean. But if harmful substances, such as cigarette smoke, are inhaled, the cilia stop functioning properly, causing health problems like bronchitis . Mucus produced by cells in the trachea and bronchial tubes keeps air passages moist and aids in stopping dust, bacteria and viruses, allergy -causing substances, and other substances from entering the lungs. Impurities that do reach the deeper parts of the lungs can often be moved up via mucous and coughed out or swallowed.

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He has a master's degree in writing and literature. Did you know that the average human lung has a respiratory surface area that is roughly the same size as half of a tennis court? Believe it or not, that's how much surface area an active, healthy human needs to ensure that the body gets plenty of oxygen. Why Doesn't the Skin Absorb Oxygen? Let's talk about the human respiratory system and why we need it. I mean, we're all surrounded by the air, which is about 20% oxygen, so why don't we just absorb it through our skin? The problem is, if we just absorbed oxygen through our skin, it might reach the first two, maybe three layers of cells, before it was all used up, and it would never make it all the way to our brain, or muscles, or most other places in our body. We just don't have enough surface area to supply enough oxygen and we need an efficient way to get it into the bloodstream so that it can be distributed throughout the body. The trachea splits into the bronchi Parts of the Respiratory System So, let's start at the beginning. A person breathes air in through their nostrils or their mouth.

The mouth and nasal airways come together at a junction called the pharynx, which is located at the back of the mouth, and continues down the throat until it reaches the larynx. The larynx is more commonly known as the voice box, and some people call it the Adam's apple. The air then enters the trachea, which is the main airway that runs from the larynx down to the lungs. The trachea is known to most people as the windpipe. Just as the air reaches the lungs, the trachea splits into two smaller tubes called bronchi. Each bronchus enters one side of the lungs and then splits repeatedly into ever smaller tubes called bronchioles . The Alveoli And finally, at the ends of the smallest bronchioles are clusters of spherical structures that look a lot like bunches of grapes. These grape-like structures are called alveoli and are basically tiny air sacs with very thin walls that serve as the main site of gas exchange. Alveoli clusters create a honeycomb-like structure The average human lung has about 500 million alveoli with a combined inner surface area that is about the same size as half of a full-size tennis court.

That's 40 times the surface area of a person's skin! So how is this even possible? The organization of the alveoli in clusters creates a honeycomb-like internal structure where the alveoli walls create a massive amount of surface area for the air to come in contact with. In combination with the sheer numbers of the alveoli, they solve our first problem by increasing the surface area available to absorb oxygen through. But how do the lungs take oxygen out of the air and get it into the bloodstream? Well, surrounding the alveoli is a very dense network of capillaries . You may remember that capillaries are very small, flattened blood vessels with very thin walls that allow gases and nutrients to be easily transferred between the blood and surrounding tissues. How Blood Becomes Oxygenated The blood collects oxygen from the alveoli as it passes over the entire surface area, created by the alveolar walls. However, the oxygen can't just magically jump from the air across the alveoli and into the blood; it has to cross each barrier one at a time. First, the oxygen has to be dissolved, so there is a thin film of water coating the inside surface of the alveoli.

Because the volume of water is so small, it becomes saturated with oxygen almost instantly and the oxygen is then free to diffuse across the cell membrane. You may recall that dissolved molecules diffuse quickly in the direction of a lower concentration, which in this case is the oxygen-depleted blood in the surrounding capillaries, so oxygen diffuses from the saturated water coating the alveoli, across the alveolar wall, through the capillary wall and into the oxygen-depleted blood. Once in the blood, you may also remember that oxygen enters red blood cells and then binds to hemoglobin, taking it out of solution and keeping the dissolved oxygen level low in the blood. This ensures that the oxygen continues to flow from the alveoli and into the blood. × Respiratory System The Respiratory System and Gas Exchange | Back to Top Cellular respiration involves the breakdown of organic molecules to produce ATP . A sufficient supply of oxygen is required for the aerobic respiratory machinery of Kreb's Cycle and the Electron Transport System to efficiently convert stored organic energy into energy trapped in ATP. Carbon dioxide is also generated by cellular metabolism and must be removed from the cell. There must be an exchange of gases: carbon dioxide leaving the cell, oxygen entering.

Animals have organ systems involved in facilitating this exchange as well as the transport of gases to and from exchange areas. Bodies and Respiration | Back to Top Single-celled organisms exchange gases directly across their cell membrane. However, the slow diffusion rate of oxygen relative to carbon dioxide limits the size of single-celled organisms. Simple animals that lack specialized exchange surfaces have flattened, tubular, or thin shaped body plans, which are the most efficient for gas exchange. However, these simple animals are rather small in size. Respiratory Surfaces | Back to Top Large animals cannot maintain gas exchange by diffusion across their outer surface. They developed a variety of respiratory surfaces that all increase the surface area for exchange, thus allowing for larger bodies. A respiratory surface is covered with thin, moist epithelial cells that allow oxygen and carbon dioxide to exchange. Those gases can only cross cell membranes when they are dissolved in water or an aqueous solution, thus respiratory surfaces must be moist. Methods of Respiration | Back to Top Sponges and jellyfish lack specialized organs for gas exchange and take in gases directly from the surrounding water. Flatworms and annelids use their outer surfaces as gas exchange surfaces.

Arthropods, annelids, and fish use gills; terrestrial vertebrates utilize internal lungs. Gas exchange systems in several animals. Images from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates ( ) and WH Freeman ( ), used with permission. The Body Surface Flatworms and annelids use their outer surfaces as gas exchange surfaces. Earthworms have a series of thin-walled blood vessels known as capillaries. Gas exchange occurs at capillaries located throughout the body as well as those in the respiratory surface. Amphibians use their skin as a respiratory surface. Frogs eliminate carbon dioxide 2.5 times as fast through their skin as they do through their lungs. Eels (a fish) obtain 60% of their oxygen through their skin. Humans exchange only 1% of their carbon dioxide through their skin. Constraints of water loss dictate that terrestrial animals must develop more efficient lungs. Gills Gills greatly increase the surface area for gas exchange. They occur in a variety of animal groups including arthropods (including some terrestrial crustaceans), annelids, fish, and amphibians.

Gills typically are convoluted outgrowths containing blood vessels covered by a thin epithelial layer. Typically gills are organized into a series of plates and may be internal (as in crabs and fish) or external to the body (as in some amphibians). Gills are very efficient at removing oxygen from water: there is only 1/20 the amount of oxygen present in water as in the same volume of air. Water flows over gills in one direction while blood flows in the opposite direction through gill capillaries. This countercurrent flow maximizes oxygen transfer. Countercurrent flow in a fish. Images from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates ( ) and WH Freeman ( ), used with permission. Tracheal Systems Many terrestrial animals have their respiratory surfaces inside the body and connected to the outside by a series of tubes. Tracheae are these tubes that carry air directly to cells for gas exchange. Spiracles are openings at the body surface that lead to tracheae that branch into smaller tubes known as tracheoles. Body movements or contractions speed up the rate of diffusion of gases from tracheae into body cells.

However, tracheae will not function well in animals whose body is longer than 5 cm. Respiratory system in an insect. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates ( ) and WH Freeman ( ), used with permission. Lungs Lungs are ingrowths of the body wall and connect to the outside by as series of tubes and small openings. Lung breathing probably evolved about 400 million years ago. Lungs are not entirely the sole property of vertebrates, some terrestrial snails have a gas exchange structures similar to those in frogs. Lungs in a bird (top) and amphibian (bottom). Images from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates ( ) and WH Freeman ( ), used with permission. Respiratory System Principles | Back to Top Movement of an oxygen-containing medium so it contacts a moist membrane overlying blood vessels. Diffusion of oxygen from the medium into the blood. Transport of oxygen to the tissues and cells of the body. Diffusion of oxygen from the blood into cells. Carbon dioxide follows a reverse path. Functional unit of a mammalian lung.

Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates ( ) and WH Freeman ( ), used with permission. The Human Respiratory System | Back to Top This system includes the lungs, pathways connecting them to the outside environment, and structures in the chest involved with moving air in and out of the lungs. The human respiratory system. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates ( ) and WH Freeman ( ), used with permission. Air enters the body through the nose, is warmed, filtered, and passed through the nasal cavity. Air passes the pharynx (which has the epiglottis that prevents food from entering the trachea).The upper part of the trachea contains the larynx . The vocal cords are two bands of tissue that extend across the opening of the larynx. After passing the larynx, the air moves into the bronchi that carry air in and out of the lungs. The lungs and alveoli and their relationship to the diaphragm and capillaries.

Images from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates ( ) and WH Freeman ( ), used with permission. Bronchi are reinforced to prevent their collapse and are lined with ciliated epithelium and mucus-producing cells. Bronchi branch into smaller and smaller tubes known as bronchioles . Bronchioles terminate in grape-like sac clusters known as alveoli . Alveoli are surrounded by a network of thin-walled capillaries . Only about 0.2 µm separate the alveoli from the capillaries due to the extremely thin walls of both structures. Gas exchange across capillary and alveolus walls. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates ( ) and WH Freeman ( ), used with permission. The lungs are large, lobed, paired organs in the chest (also known as the thoracic cavity ). Thin sheets of epithelium ( pleura ) separate the inside of the chest cavity from the outer surface of the lungs. The bottom of the thoracic cavity is formed by the diaphragm . Ventilation is the mechanics of breathing in and out.

When you inhale, muscles in the chest wall contract, lifting the ribs and pulling them, outward. The diaphragm at this time moves downward enlarging the chest cavity. Reduced air pressure in the lungs causes air to enter the lungs. Exhaling reverses theses steps. Inhalation and exhalation. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates ( ) and WH Freeman ( ), used with permission. Diseases of the Respiratory System | Back to Top The condition of the airways and the pressure difference between the lungs and atmosphere are important factors in the flow of air in and out of lungs. Many diseases affect the condition of the airways. Asthma narrows the airways by causing an allergy-induced spasms of surrounding muscles or by clogging the airways with mucus . Bronchitis is an inflammatory response that reduces airflow and is caused by long-term exposure to irritants such as cigarette smoke, air pollutants, or allergens . Cystic fibrosis is a genetic defect that causes excessive mucus production that clogs the airways.

The Alveoli and Gas Exchange | Back to Top Diffusion is the movement of materials from a higher to a lower concentration. The differences between oxygen and carbon dioxide concentrations are measured by partial pressures. The greater the difference in partial pressure the greater the rate of diffusion. Respiratory pigments increase the oxygen-carrying capacity of the blood. Humans have the red-colored pigment hemoglobin as their respiratory pigment. Hemoglobin increases the oxygen-carrying capacity of the blood between 65 and 70 times. Each red blood cell has about 250 million hemoglobin molecules, and each milliliter of blood contains 1.25 X 1015 hemoglobin molecules. Oxygen concentration in cells is low (when leaving the lungs blood is 97% saturated with oxygen), so oxygen diffuses from the blood to the cells when it reaches the capillaries. Effectiveness of various oxygen carrying molecules. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates ( ) and WH Freeman ( ), used with permission.

Carbon dioxide concentration in metabolically active cells is much greater than in capillaries, so carbon dioxide diffuses from the cells into the capillaries. Water in the blood combines with carbon dioxide to form bicarbonate . This removes the carbon dioxide from the blood so diffusion of even more carbon dioxide from the cells into the capillaries continues yet still manages to "package" the carbon dioxide for eventual passage out of the body. Details of gas exchange. Images from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates ( ) and WH Freeman ( ), used with permission. In the alveoli capillaries, bicarbonate combines with a hydrogen ion (proton) to form carbonic acid, which breaks down into carbon dioxide and water. The carbon dioxide then diffuses into the alveoli and out of the body with the next exhalation. Control of Respiration | Back to Top Muscular contraction and relaxation controls the rate of expansion and constriction of the lungs. These muscles are stimulated by nerves that carry messages from the part of the brain that controls breathing, the medulla . Two systems control breathing: an automatic response and a voluntary response. Both are involved in holding your breath.

Although the automatic breathing regulation system allows you to breathe while you sleep, it sometimes malfunctions. Apnea involves stoppage of breathing for as long as 10 seconds, in some individuals as often as 300 times per night. This failure to respond to elevated blood levels of carbon dioxide may result from viral infections of the brain, tumors, or it may develop spontaneously. A malfunction of the breathing centers in newborns may result in SIDS (sudden infant death syndrome) . As altitude increases, atmospheric pressure decreases. Above 10,000 feet decreased oxygen pressures causes loading of oxygen into hemoglobin to drop off, leading to lowered oxygen levels in the blood. The result can be mountain sickness (nausea and loss of appetite). Mountain sickness does not result from oxygen starvation but rather from the loss of carbon dioxide due to increased breathing in order to obtain more oxygen. Your Lungs & Respiratory System Your Lungs & Respiratory System What's something that you do all day, every day, no matter where you are or who you're with?

(a) think about what's for lunch tomorrow (b) put your finger in your nose (c) hum your favorite song (d) breathe It's possible that some kids could say (a) or (c) or that others might even say — yikes! — (b). But every single person in the world has to say (d). Breathing air is necessary for keeping humans (and many animals) alive. And the two parts that are large and in charge when it comes to breathing? If you guessed your lungs, you're right! Your lungs make up one of the largest organs in your body, and they work with your respiratory system to allow you to take in fresh air, get rid of stale air, and even talk. Let's take a tour of the lungs! Locate Those Lungs Your lungs are in your chest, and they are so large that they take up most of the space in there. You have two lungs, but they aren't the same size the way your eyes or nostrils are. Instead, the lung on the left side of your body is a bit smaller than the lung on the right. This extra space on the left leaves room for your heart.

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: DY-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! continue A Look Inside the Lungs From the outside, lungs are pink and a bit squishy, like a sponge. But the inside contains the real lowdown on the lungs! At the bottom of the trachea (say: TRAY-kee-uh), or windpipe, there are two large tubes.

These tubes are called the main stem bronchi (say: BRONG-kye), and one heads left into the left lung, while the other heads right into the right lung. Each main stem bronchus (say: BRONG-kuss) — the name for just one of the bronchi — then branches off into tubes, or bronchi, that get smaller and even smaller still, like branches on a big tree. The tiniest tubes are called bronchioles (say: BRONG-kee-oles), and there are about 30,000 of them in each lung. Each bronchiole is about the same thickness as a hair. At the end of each bronchiole is a special area that leads into clumps of teeny tiny air sacs called alveoli (say: al-VEE-oh-lie). There are about 600 million alveoli in your lungs and if you stretched them out, they would cover an entire tennis court. Now that's a load of alveoli!

Each alveolus (say: al-VEE-oh-luss) — what we call just one of the alveoli — has a mesh-like covering of very small blood vessels called capillaries (say: CAP-ill-er-ees). These capillaries are so tiny that the cells in your blood need to line up single file just to march through them. All About Inhaling When you're walking your dog, cleaning your room, or spiking a volleyball, you probably don't think about inhaling (breathing in) — you've got other things on your mind! But every time you inhale air, dozens of body parts work together to help get that air in there without you ever thinking about it. As you breathe in, your diaphragm contracts and flattens out. This allows it to move down, so your lungs have more room to grow larger as they fill up with air. "Move over, diaphragm, I'm filling up!" is what your lungs would say. And the diaphragm isn't the only part that gives your lungs the room they need. Your rib muscles also lift the ribs up and outward to give the lungs more space.

At the same time, you inhale air through your mouth and 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. previous continue Thank You, Alveoli! 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 vessels to the heart.

The heart then sends the oxygenated (filled with oxygen) blood out to all the cells in the body. Waiting to Exhale When it's time to exhale (breathe out), everything happens in reverse: Now it's the diaphragm's turn to say, "Move it!" Your diaphragm relaxes and moves up, pushing air out of the lungs. Your rib muscles become relaxed, and your ribs move in again, creating a smaller space in your chest. By now your cells have used the oxygen they need, and your blood is carrying carbon dioxide and other wastes that must leave your body. The blood comes back through the capillaries and the wastes enter the alveoli. Then you breathe them out in the reverse order of how they came in — the air goes through the bronchioles, out the bronchi, out the trachea, and finally out through your mouth and nose. 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 (say: PLOO-ral) membranes. These membranes are separated by a fluid that allows them to slide around easily while you inhale and exhale. previous continue Time for Talk Your lungs are important for breathing . . . and also for talking! Above the trachea (windpipe) is the larynx (say: LAIR-inks), which is sometimes called the voice box. Across the voice box are two tiny ridges called vocal cords, which open and close to make sounds. When you exhale air from the lungs, it comes through the trachea and larynx and reaches the vocal cords. If the vocal cords are closed and the air flows between them, the vocal cords vibrate and a sound is made. The amount of air you blow out from your lungs determines how loud a sound will be and how long you can make the sound.

Try inhaling very deeply and saying the names of all the kids in your class — how far can you get without taking the next breath? The next time you're outside, try shouting and see what happens — shouting requires lots of air, so you'll need to breathe in more frequently than you would if you were only saying the words. Experiment with different sounds and the air it takes to make them — when you giggle, you let out your breath in short bits, but when you burp , you let swallowed air in your stomach out in one long one! When you hiccup, it's because the diaphragm moves in a funny way that causes you to breathe in air suddenly, and that air hits your vocal cords when you're not ready. Love 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 smart 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 get hurt 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! How Lungs Work | American Lung Association See what healthy lungs can do for you Every cell in your body needs oxygen in order to live. The air we breathe contains oxygen and other gases. Once in the lungs, oxygen is moved into the bloodstream and carried through your body. At each cell in your body, oxygen is exchanged for a waste gas called carbon dioxide. Your bloodstream then carries this waste gas back to the lungs where it is removed from the blood stream and then exhaled. Your lungs and respiratory system automatically perform this vital process, called gas exchange. In addition to gas exchange, your respiratory system performs other roles important to breathing. These include: Bringing air to the proper body temperature and moisturizing it to the right humidity level. Protecting your body from harmful substances. This is done by coughing, sneezing, filtering or swallowing them. Supporting your sense of smell.

The Parts of the Respiratory System and How They Work Airways SINUSES are hollow spaces in the bones of your head above and below your eyes that are connected to your nose by small openings. Sinuses help regulate the temperature and humidity of inhaled air. The NOSE is the preferred entrance for outside air into the respiratory system. The hairs lining the nose's wall are part of the air-cleaning system. Air also enters through the MOUTH, especially for those who have a mouth-breathing habit, whose nasal passages may be temporarily blocked by a cold, or during heavy exercise. The THROAT collects incoming air from your nose and mouth then passes it downward to the windpipe (trachea). The WINDPIPE (trachea) is the passage leading from your throat to your lungs. The windpipe divides into the two main BRONCHIAL TUBES, one for each lung, which divides again into each lobe of your lungs. These, in turn, split further into bronchioles. Lungs and Blood Vessels Your right lung is divided into three LOBES, or sections. Each lobe is like a balloon filled with sponge-like tissue.

Air moves in and out through one opening—a branch of the bronchial tube. Your left lung is divided into two LOBES. The PLEURA are the two membranes, actually one continuous one folded on itself, that surround each lobe of the lungs and separate your lungs from your chest wall. Your bronchial tubes are lined with CILIA (like very small hairs) that move like waves. This motion carries MUCUS (sticky phlegm or liquid) upward and out into your throat, where it is either coughed up or swallowed. Mucus catches and holds much of the dust, germs, and other unwanted matter that has invaded your lungs. You get rid of this matter when you cough, sneeze, clear your throat or swallow. The smallest branches of the bronchial tubes are called BRONCHIOLES, at the end of which are the air sacs or alveoli. ALVEOLI are the very small air sacs that are the destination of breathed-in air. CAPILLARIES are blood vessels in the walls of the alveoli. Blood passes through the capillaries, entering through your PULMONARY ARTERY and leaving via your PULMONARY VEIN.

While in the capillaries, blood gives off carbon dioxide through the capillary wall into the alveoli and takes up oxygen from air in the alveoli. Muscles and Bones Your DIAPHRAGM is the strong wall of muscle that separates your chest cavity from the abdominal cavity. By moving downward, it creates suction in the chest, drawing in air and expanding the lungs. RIBS are bones that support and protect your chest cavity. They move slightly to help your lungs expand and contract. Keeping Lungs Healthy Lung capacity declines as you age . Keep your lungs healthy by taking good care of yourself every day. Eat a balanced diet, exercise and reduce stress to breathe easier. Get more tips for healthy lungs » Related Content Alveoli - Definition, Structure, and Function in the Lungs Pneumoconioses (such as black lung disease.) Rare diseases such as pulmonary alveolar lung disease and others also affect the alveoli. The Oxygen Journey: Following the Travel of Oxygen and Carbon Dioxide From the Air to the Body and Back To understand the function of the alveoli, it can help to follow the flow of gases (oxygen and carbon dioxide) from the atmosphere to the body and back.

Inspiration - Oxygen in the air is first inhaled through the mouth or the nose. It then travels down past the trachea and enters either the left bronchus or right bronchus to travel to the respective lung. From the bronchi, air containing oxygen travels to the bronchioles and then to the respiratory bronchioles (the smallest bronchioles.) It reaches the alveolar duct, and then one of the alveoli clustered around the alveolar duct like grapes. Oxygen Exchange - Once oxygen is present in an alveolus it diffuses first into the fluid of the alveolus ( surfactant ) and through the single-celled wall of the alveolus, then through the single-celled wall of the capillary and into the plasma. It does so by diffusion since the oxygen concentration is lower in the blood of the capillary than it is in the alveolus. Within the blood of the capillary oxygen then binds to hemoglobin floating in the plasma. Each molecule of hemoglobin carries 4 molecules of oxygen.

Flow of Oxygen and Cellular Respiration – Oxygen is carried on hemoglobin in the blood on from the capillary through arterioles and arteries and back to capillaries, to all of the tissues and organs in the body. From tissue capillaries, this oxygen then diffuses into cells due to a lower concentration of oxygen being in the cells than in the plasma. Oxygen is then used by the body in the process of cellular respiration which results in the production of carbon dioxide. Flow of Carbon Dioxide - Carbon dioxide produced in the cells then diffuses from the cell into capillaries, into veins (from small to large,) to the right side of the heart, and back to the lungs via the pulmonary arteries. The pulmonary arteries then branch into smaller arteries and arterioles until they reach the capillaries near the alveoli in the lungs. Carbon Dioxide Exchange - From the plasma in capillaries, carbon dioxide diffuses into the alveoli, as the carbon dioxide concentration in the alveoli is lower than that in the capillaries.

Expiration - Carbon dioxide then travels in a reverse direction of the oxygen through the respiratory tract, traveling from alveoli, through the alveolar ducts, bronchioles, bronchi, and trachea, to exit through the mouth or nose. Sources: Hamid, Q., Shannon, J., and J. Martin. The Physiologic Basis of Respiratory Disease. PMPH-USA. 2005. Sharafkhaneh, A., Hanania, N., and V. Kim. Pathogenesis of Emphysema . Proceedings of the American Thoracic Society. 2008. 5:475-77. U.S. National Library of Medicine. Medline Plus. Gas exchange. Updated 10/27/14. U.S. National Library of Medicine. PubMed Health. Alveoli. Accessed 09/20/15. Continue Reading The Lungs (Human Anatomy): Picture, Function, Definition, Conditions Human Anatomy Picture of the Lungs © 2014 WebMD, LLC. All rights reserved. The lungs are a pair of spongy, air-filled organs located on either side of the chest (thorax).

The trachea (windpipe) conducts inhaled air into the lungs through its tubular branches, called bronchi. The bronchi then divide into smaller and smaller branches (bronchioles), finally becoming microscopic. The bronchioles eventually end in clusters of microscopic air sacs called alveoli. In the alveoli, oxygen from the air is absorbed into the blood . Carbon dioxide , a waste product of metabolism , travels from the blood to the alveoli, where it can be exhaled. Between the alveoli is a thin layer of cells called the interstitium, which contains blood vessels and cells that help support the alveoli. The lungs are covered by a thin tissue layer called the pleura. The same kind of thin tissue lines the inside of the chest cavity -- also called pleura. A thin layer of fluid acts as a lubricant allowing the lungs to slip smoothly as they expand and contract with each breath. Lung Conditions Chronic obstructive pulmonary disease ( COPD ): Damage to the lungs results in difficulty blowing air out, causing shortness of breath. Smoking is by far the most common cause of COPD. Emphysema : A form of COPD usually caused by smoking .

The fragile walls between the lungs' air sacs (alveoli) are damaged, trapping air in the lungs and making breathing difficult. Chronic bronchitis : Repeated, frequent episodes of productive cough, usually caused by smoking . Breathing also becomes difficult in this form of COPD. Pneumonia : Infection in one or both lungs. Bacteria, especially Streptococcus pneumoniae, are the most common cause. Asthma : The lungs' airways (bronchi) become inflamed and can spasm, causing shortness of breath and wheezing . Allergies , viral infections , or air pollution often trigger asthma symptoms . Acute bronchitis : An infection of the lungs' large airways (bronchi), usually caused by a virus. Cough is the main symptom of acute bronchitis . Pulmonary fibrosis : A form of interstitial lung disease . The interstitium (walls between air sacs) become scarred, making the lungs stiff and causing shortness of breath. Sarcoidosis : Tiny areas of inflammation can affect all organs in the body, with the lungs involved most of the time.

The symptoms are usually mild; sarcoidosis is usually found when X-rays are done for other reasons. Obesity hypoventilation syndrome: Extra weight makes it difficult to expand the chest when breathing. This can lead to long-term breathing problems . Pleural effusion : Fluid builds up in the normally tiny space between the lung and the inside of the chest wall (the pleural space). If large, pleural effusions can cause problems with breathing. Pleurisy : Inflammation of the lining of the lung (pleura), which often causes pain when breathing in. Autoimmune conditions, infections, or a pulmonary embolism may cause pleurisy . Bronchiectasis: The airways (bronchi) become inflamed and expand abnormally, usually after repeated infections. Coughing , with large amounts of mucus, is the main symptom of bronchiectasis. Lymphangioleiomyomatosis ( LAM ): A rare condition in which cysts form throughout the lungs, causing breathing problems similar to emphysema . LAM occurs almost exclusively in women of childbearing age. Cystic fibrosis : A genetic condition in which mucus does not clear easily from the airways.

The excess mucus causes repeated episodes of bronchitis and pneumonia throughout life. Interstitial lung disease : A collection of conditions in which the interstitium (lining between the air sacs) becomes diseased. Fibrosis (scarring) of the interstitium eventually results, if the process can't be stopped. Lung cancer : Cancer may affect almost any part of the lung. Most lung cancer is caused by smoking . Lungs, Lungs Information, Breathing Facts, News, Photos -- National Geographic This requires the latest version of Flash Player. Click here to download. Our lungs fuel us with oxygen, the body's life-sustaining gas. They breathe in air, then extract the oxygen and pass it into the bloodstream, where it's rushed off to the tissues and organs that require it to function. Oxygen drives the process of respiration, which provides our cells with energy. The waste gas carbon dioxide is produced as a byproduct and disposed of when we exhale. Without this vital exchange our cells would quickly die and leave the body to suffocate. Since the lungs process air, they are the only internal organs that are constantly exposed to the external environment.

Central to the human respiratory system, they breathe in between 2,100 and 2,400 gallons (8,000 and 9,000 liters) of air each day—the amount needed to oxygenate the 2,400 gallons (9,000 liters) or so of blood that is pumped through the heart daily. Intricate Construction Our two lungs are made up of a complex latticework of tubes, which are suspended, on either side of the heart, inside the chest cavity on a framework of elastic fibers. Air is drawn in via the mouth and the nose, the latter acting as an air filter by trapping dust particles on its hairs. The air is warmed up before passing down the windpipe, where it's divided at the bottom between two airways called bronchi that lead to either lung. Within the lungs, the mucus-lined bronchi split like the branches of a tree into tens of thousands of ever smaller tubes (bronchioles), which connect to tiny sacs called alveoli. The average adult's lungs contain about 600 million of these spongy, air-filled structures.

There are enough alveoli in just one lung to cover an area roughly the size of a tennis court. The alveoli are where the crucial gas exchange takes place. The air sacs are surrounded by a dense network of minute blood vessels, or capillaries, which connect to the heart. Those that link to the pulmonary arteries carry deoxygenated blood that needs to be refreshed. Oxygen passes through the incredibly thin walls of the alveoli into the capillaries and is then carried back to the heart via the pulmonary veins. At the same time, carbon dioxide is removed from the blood through the same process of diffusion. This waste gas is expelled as we breathe out. The rate at which we breathe is controlled by the brain, which is quick to sense changes in gas concentrations. This is certainly in the brain's interests—it's the body's biggest user of oxygen and the first organ to suffer if there's a shortage. In and Out The actual job of breathing is done mainly by the diaphragm, the sheet of muscles between the chest and abdomen. These muscles contract when we breathe in, expanding the lungs and drawing in air. We breathe out simply by relaxing the diaphragm; the lungs deflate like balloons.

Lungs are delicate organs and vulnerable to a range of illnesses. The most common of these in Western countries are bronchitis and emphysema, which are often caused by smoking. Tubes inside the lung become chronically inflamed, producing excess mucus. Smoking can also lead to lung cancer, the world's major cancer, which is diagnosed in 1.4 million people a year.

Question: Where in the human body do you find the alveoli?
Answer: Lung