What Breathing Does for the Body - How the Lungs Work - What Breathing Does for the Body 

Breathing involves two phases: breathing in and breathing out. Your lungs deliver oxygen and remove carbon dioxide from your blood in a process called gas exchange. Gas exchange happens in the capillaries surrounding the alveoli, where the oxygen that is breathed in enters the circulatory system and carbon dioxide in the blood is released to the lungs and then breathed out. If you have problems breathing, gas exchange may be impaired, increasing the risk of serious health problems.

Breathing in
- How the Lungs Work - What Breathing Does for the Body
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

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. Here the oxygen you inhaledi 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 © 2019 Nucleus Medical Media Inc. All rights reserved.

Through the very 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 the capillaries into the air sacs. This process of exchanging oxygen for carbon dioxide is called gas exchange. The oxygen in your blood is stored inside your red blood cells by a protein called hemoglobin.

The oxygen-rich blood from the lungs is carried to the left side of the heart through the pulmonary veins. The left side of the heart pumps the blood to the rest of the body. There, the oxygen in the red blood cells moves from blood vessels into surrounding tissues.

As carbon dioxide is released from the cells of the body, it travels in the bloodstream to the heart. The blood rich in carbon dioxide is then pumped from the right side of the heart through the pulmonary artery to the lungs, where gas exchange occurs.

For more information on blood flow, visit our How the Heart Works Health Topic.

Breathing out
- How the Lungs Work - What Breathing Does for the Body
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 the 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.

Conditions that affect the respiratory system

- How the Lungs Work - What Breathing Does for the Body
Damage, infection, or inflammation in the lungs or airways or both can lead to the following conditions.

• Asbestos-related lung diseases
• Asthma
• Atelectasis
• Bronchitis
• COPD
• Hypersensitivity pneumonitis
• Idiopathic pulmonary fibrosis
• Pleural Disorders
• Pneumonia
• Primary ciliary dyskinesia
• Sarcoidosis

​Exposure to cigarette smoke, air pollutants, or other substances can damage the airways, causing disease of the airways or making a disease more severe.

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How Your Body Controls Breathing - How the Lungs Work - How Your Body Controls Breathing​
The body’s muscles and nervous system help control your breathing.

The pleura and diaphragm. Your lungs are encased by pleura, a thin membrane that protects them and helps them slide back and forth as you breathe in and out. Underneath your lungs is the diaphragm, a smooth thin muscle that helps your lungs expand and contract as you breathe. Medical Animation Copyright © 2019 Nucleus Medical Media Inc. All rights reserved.

The pleura and the muscles used for breathing
- How the Lungs Work - How Your Body Controls Breathing
The lungs are enclosed by the pleura, a membrane that has two layers. The space between these two layers is called the pleural cavity. The membrane’s cells create pleural fluid, which acts as a lubricant to reduce friction during breathing.
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The lungs are like sponges; they cannot move on their own. Muscles in your chest and abdomen contract, or tighten, to create space in your lungs for air to flow in. The muscles then relax, causing the space in the chest to get smaller and squeeze the air back out.

These muscles include the:

• Diaphragm, which is a dome-shaped muscle below your lungs. It separates the chest cavity from the abdominal cavity. The diaphragm is the main muscle used for breathing.
• Intercostal muscles, which are located between your ribs. They also play a major role in helping you breathe.
• Abdominal muscles. They help you breathe out when you are breathing fast, such as during physical activity.
• Muscles of the face, mouth, and pharynx. The pharynx is the part of the throat right behind the mouth. These muscles control the lips, tongue, soft palate, and other structures to help with breathing. Problems with these muscles can cause sleep apnea.
• Muscles in the neck and collarbone area. These muscles help you breathe in when other muscles involved in breathing are not working well or when lung disease impairs your breathing.

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.

Role of the nervous system
- How the Lungs Work - How Your Body Controls Breathing
Your breathing usually does not require any thought, because it is controlled by the autonomic nervous system, also called the involuntary nervous system. The autonomic nervous system has different effects on your breathing.

• The parasympathetic nervous system tells the diaphragm and intercostal muscles to tighten and relax more quickly or more slowly to adjust your breathing rate in response to carbon dioxide and oxygen levels in the brain. This system also causes your bronchial tubes to narrow and the pulmonary blood vessels to widen.
• The sympathetic nervous system increases your breathing rate through what is called the fight-or-flight response. When this system is activated, it releases a chemical signal called norepinephrine that makes your bronchial tubes widen and the pulmonary blood vessels narrow.

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. In contrast, your body needs to restrict how much air you breathe if the air contains irritants or toxins. 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 help your respiratory system provide enough oxygen to the body while removing carbon dioxide. The sensors transmit signals to the centers of the brain involved in breathing. These sensors include:

• Sensors in the airways that detect lung irritants. The sensors can trigger sneezing or coughing. In people who have asthma, the sensors may cause the muscles around the airways in the lungs to contract. This makes the airways smaller.
• Sensors in the brain and in two blood vessels, the aorta and the carotid artery in the neck, that detect carbon dioxide or oxygen levels in your blood and change your breathing rate as needed.
• Sensors in your joints and muscles that detect the movement of your arms or legs. These sensors may play a role in increasing your breathing rate when you are physically active.

Some health conditions can interfere with brain signals to the airways and chest muscles, causing central sleep apnea. In central sleep apnea, the respiratory centers of the brain do not respond properly to rising carbon dioxide levels and do not properly control the diaphragm and intercostal muscles. As a result, breathing stops for a short period. Central sleep apnea can lead to stroke and other medical conditions.

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- How the Lungs Work - How Your Body Controls Breathing

• Keeping Your Lungs Healthy will discuss lifestyle changes that can help protect your lungs from injury or disease.

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Keeping Your Lungs Healthy - How the Lungs Work - Keeping Your Lungs Healthy
You can take steps to help protect your lungs from injury or disease, including:

• Quitting smoking, or not starting if you do not smoke. Visit Smoking and Your Heart and the National Heart, Lung, and Blood Institute’s Your Guide to a Healthy Heart. Although these resources focus on heart health, they include basic information about how to quit smoking. For free help and support to quit smoking, you may call the National Cancer Institute’s Smoking Quitline at 1-877-44U-QUIT (1-877-448-7848).
• Avoiding secondhand tobacco smoke by staying away from places where smoking is allowed. Ask friends and family members who smoke not to do it in the house or car.
• Aiming for a healthy weight. Unhealthy eating patterns and lack of physical activity can lead to overweight and obesity, which can result in sleep apnea. Research has shown that losing weight can reduce sleep apnea in people who have also been diagnosed with obesity.
• Being physically active. By being physically active, you can help strengthen your heart and lungs so they work more efficiently. Physical activity may also reduce your risk of lung injury or disease. Our Move More Fact Sheet includes basic information about recommendations for physical activity. Before starting any exercise program, ask your doctor what level of physical activity is right for you.
• Limiting exposure to outdoor air pollution by checking the Air Quality Index before taking part in outdoor activities and avoiding heavy traffic when possible.
• Reducing indoor air pollution by making sure that the places where you live and work are well ventilated and cleaned regularly to prevent the buildup of allergens, dust, and mold. You can also remove products that create fumes, such as strong cleaning products and aerosols. Avoid burning solid fuels such as wood for heating and cooking.
• Taking precautions against seasonal flu and pneumonia. Get a flu shot every year. You may also want to ask your doctor or healthcare provider about the pneumonia vaccine.
• Testing your home for radon gas. Radon is a colorless, tasteless, and odorless gas that forms naturally. It can enter buildings through cracks in the wall and can cause lung cancer. Inexpensive testing kits are available from many hardware stores. If radon levels are hazardous, take recommended steps to reduce radon levels in your home, or alert the property owners so they can fix the building.
• Using protective gear if you work in an industry that involves exposure to dust, silica, allergens, chemical fumes, or other indoor or outdoor air pollution.

​How do your lungs change as you get older?
Read moreAs 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.
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• Research for Your Health will discuss how we are using current research and advancing research to prevent lung injury and disease.
• Participate in NHLBI Clinical Trials will explain our open and enrolling clinical studies that are investigating prevention strategies for lung injury and disease.

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