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Your lungs are a pair of organs in your chest. They have a spongy texture and are pinkish-gray in color.
When you inhale (breathe in), air enters your lungs and oxygen from the air moves from your lungs to your blood. At the same time, carbon dioxide, a waste gas, moves from your blood to the lungs and is exhaled (breathe out). This process is called gas exchange and is essential to life.
In addition to the lungs, your respiratory system includes the trachea (windpipe), muscles of the chest wall and diaphragm, blood vessels, and tissues that make breathing and gas exchange possible. Your brain controls your breathing rate (how fast or slow you breathe), by sensing your body’s need for oxygen and its need to get rid of carbon dioxide.
Healthy lifestyle habits, such as physical activity and not smoking, can help prevent lung injury and disease.
Explore this Health Topic to learn more about how the lungs work, our role in research and clinical trials, and where to find more information.
Your lungs lie on each side of your heart inside your chest cavity. The right lung is divided into three lobes (sections), and the left lung is divided into two lobes. Your left lung is slightly smaller than your right lung, since your heart takes up some space on the left side. When you breathe in, air enters your airways and travels down into the alveoli (air sacs) in your lungs. This is where gas exchange takes place.
Your lungs. Your lungs are two spongy organs in your chest. The left lung is divided into two lobes and the right lung is divided into three lobes. Medical Animation Copyright © 2019 Nucleus Medical Media Inc. All rights reserved.
The circulatory system, which is made up of the heart and blood vessels, supports the respiratory system by bringing blood to and from the lungs. The circulatory system helps to deliver nutrients and oxygen from the lungs to tissues and organs throughout the body and removes carbon dioxide and waste products. Other body systems that work with the respiratory system include the nervous system, lymphatic system, and immune system.
The airways are pipes that carry oxygen-rich air to the alveoli in your lungs. They also carry the waste gas carbon dioxide out of your lungs. The airways include these parts of your body:
Breathing air into your lungs. When you breathe in, air enters your nose and/or mouth, and passes into your windpipe, also called the trachea. The windpipe divides into two bronchial tubes, or bronchi, then branches into smaller bronchioles. The bronchioles end in tiny air sacs, called alveoli. Here the oxygen you inhale passes into the bloodstream, and carbon dioxide from your body passes out of the bloodstream into the air in your lungs. The carbon dioxide is expelled from your body when you exhale. Medical Animation Copyright © 2020 Nucleus Medical Media Inc. All rights reserved.
Air first enters your body through your nose or mouth, which moistens and warms the air since cold, dry air can irritate your lungs. The air then travels past your voice box and down your windpipe. Rings of tough tissue, called cartilage, acts as a support to keep the bronchial tubes open.
Inside your lungs, the bronchial tubes branch into thousands of thinner tubes called bronchioles. The bronchioles end in clusters of tiny air sacs called alveoli.
Your lungs have about 150 million alveoli. Normally, your alveoli are elastic, meaning that their size and shape can change easily. Alveoli are able to easily expand and contract, because their insides are coated with a substance called surfactant. Surfactant reduces the work it takes to breathe by helping the lungs inflate more easily when you breathe in and preventing the lungs from collapsing when you breath out.
Each of these alveoli is made up of a mesh of tiny blood vessels called capillaries. The capillaries connect to a network of arteries and veins that move blood through your body.
The pulmonary artery and its branches deliver blood to the capillaries that surround the alveoli. This blood is rich in carbon dioxide and low in oxygen.
Carbon dioxide moves from the blood into the air inside the alveoli. At the same time, oxygen moves from the air into the blood in the capillaries.
How does my body protect the airways from food or bacteria?
When you swallow, a thin flap of tissue called the epiglottis covers your windpipe. Along with coughing and gag reflexes, the epiglottis prevents food and drink from entering the airway. The epiglottis also helps direct food into your esophagus, which is the pipe that goes to your stomach.
Except for the mouth and some parts of the nose, the airways have cells that make mucus, a sticky substance that coats the walls of the airways. Other cells in the airways have hairlike structures called cilia. The cilia and mucus trap germs and other particles that enter your airways when you breathe in air. The cilia then sweep the mucus-coated germs up to the nose or mouth. From there, the germs are swallowed, coughed, or sneezed out of the body.
The lungs are surrounded by the pleura, a membrane with two layers. The space between these two layers is called the pleural cavity. A slippery liquid called pleural fluid acts as a lubricant to reduce friction during breathing.
The body’s muscles and nervous system help control your breathing.
The lungs are like sponges; they cannot expand (get bigger) on their own. Muscles in your chest and abdomen contract (tighten) to create a slight vacuum around your lungs. This causes air to flow in. When you exhale, the muscles relax and the lungs deflate on their own, much like an elastic balloon will deflate if left open to the air.
The breathing muscles include the:
Damage to the nerves in the upper spinal cord can interfere with the movement of your diaphragm and other muscles in your chest, neck, and abdomen. This can happen due to a spinal cord injury, a stroke, or a degenerative disease such as muscular dystrophy. The damage can cause respiratory failure. Ventilator support or oxygen therapy may be necessary to maintain oxygen levels in the body and protect the organs from damage.
Your breathing usually does not require any thought, because it is controlled by the autonomic nervous system, also called the involuntary nervous system.
Your breathing changes depending on how active you are and the condition of the air around you. For example, you need to breathe more often when you do physical activity. At times, you can control your breathing pattern, such as when you hold your breath or sing.
To help adjust your breathing to changing needs, your body has sensors that send signals to the breathing centers in the brain.
In central sleep apnea, the brain temporarily stops sending signals to the muscles needed to breathe. Learn more at our Sleep Apnea Health Topic.
Breathing involves two phases: breathing in and breathing out. If you have problems breathing, gas exchange may be impaired, which can be a serious health problem.
When you breathe in, or inhale, your diaphragm contracts and moves downward. This increases the space in your chest cavity, and your lungs expand into it. The muscles between your ribs also help enlarge the chest cavity. They contract to pull your rib cage both upward and outward when you inhale.
As your lungs expand, air is sucked in through your nose or mouth. The air travels down your windpipe and into your lungs. After passing through your bronchial tubes, the air travels to the alveoli, or air sacs.
Gas exchange in your lungs. When you breathe in, air enters your nose or mouth, and passes into your windpipe, also called the trachea. At the bottom, the windpipe divides into two bronchial tubes, then branches into smaller bronchioles. The brochioles end in tiny air sacs, called alveoli. In the alveoli, the oxygen you inhaled passes into the bloodstream, and carbon dioxide from your body passes out of the bloodstream. The carbon dioxide is expelled from your body when you exhale. Medical Animation Copyright © 2020 Nucleus Medical Media Inc. All rights reserved.
Through the thin walls of the alveoli, oxygen from the air passes into your blood in the surrounding capillaries. At the same time, carbon dioxide moves from your blood into the air sacs. The oxygen in your blood is carried inside your red blood cells by a protein called hemoglobin.
The oxygen-rich blood from your lungs is carried to the left side of the heart through the pulmonary veins. The heart pumps the blood to the rest of the body, where oxygen in the red blood cells moves from blood vessels into your cells.
Your cells use oxygen to make energy so your body can work. During this process, your cells also make a waste gas called carbon dioxide. Carbon dioxide needs to be breathed out or it can damage your cells.
Carbon dioxide moves from the cells into the bloodstream, where it travels to the right side of your heart. The blood rich in carbon dioxide is then pumped from the heart through the pulmonary artery to the lungs, where it is breathed out.
For more information on blood flow, visit our How the Heart Works Health Topic.
When you breathe out, or exhale, your diaphragm and rib muscles relax, reducing the space in the chest cavity. As the chest cavity gets smaller, your lungs deflate, similar to releasing of air from a balloon. At the same time, carbon dioxide-rich air flows out of your lungs through the windpipe and then out of your nose or mouth.
Breathing out requires no effort from your body unless you have a lung disease or are doing physical activity. When you are physically active, your abdominal muscles contract and push your diaphragm against your lungs even more than usual. This rapidly pushes air out of your lungs.
Damage, infection, or inflammation in the lungs or airways or both, can lead to the following conditions.
Exposure to cigarette smoke, air pollutants, or other substances can damage the airways, causing disease of the airways or making a disease more severe.
You can take these steps to help protect your lungs from injury or disease:
How do your lungs change as you get older?
As you age, the lung tissue that helps keep your airways open can lose elasticity, which means they cannot expand or contract as easily as when you were younger. The muscles your body uses for breathing may get smaller or weaker, and your spine can curve more, leaving less space for your lungs to expand. It can take longer to clear mucus and particles from your airways. It can also become harder to cough. These changes can make it harder to breathe during physical activity as you get older.
The NHLBI is part of the U.S. Department of Health and Human Services’ National Institutes of Health (NIH)—the Nation’s biomedical research agency that makes important scientific discoveries to improve health and save lives. We are committed to advancing science and translating discoveries into clinical practice to promote the prevention and treatment of heart, lung, blood, and sleep disorders. Learn about current and future NHLBI efforts to improve health through research and scientific discovery.
Learn about the following ways the NHLBI continues to translate current research to prevent and treat lung problems. Research on this topic is part of the NHLBI’s broader commitment to advancing lung disease scientific discovery.
Learn about some of the pioneering research contributions we have made over the years that have improved clinical care.
In support of our mission, we are committed to advancing lung research in part through the following ways.
Learn about exciting research areas the NHLBI is exploring about the lungs.
We lead or sponsor studies on the lungs. See if you or someone you know is eligible to participate in a clinical trials.
To learn more about clinical trials at the NIH Clinical Center or to talk to someone about a study that might fit your needs, call the Office of Patient Recruitment 800-411-1222.
Learn more about participating in a clinical trial.
View all trials from ClinicalTrials.gov.
After reading our How the Lungs Work Health Topic, you may be interested in additional information found in the following resources.
This Symposium will highlight important scientific advances in pulmonary health and disease since the creation of t...