Breathing is so vital to life that it happens automatically. Each day, you breathe about 20,000 times, and by the time you're 70 years old, you'll have taken at least 600 million breaths.
All of this breathing couldn't happen without the respiratory system, which includes the nose, throat, voice box, windpipe, and lungs.
At the top of the respiratory system, the nostrils (also called nares) act as the air intake, bringing air into the nose, where it's warmed and humidified. Tiny hairs called cilia protect the nasal passageways and other parts of the respiratory tract, filtering out dust and other particles that enter the nose through the breathed air.
Air can also be taken in through the mouth. These two openings of the airway (the nasal cavity and the mouth) meet at the pharynx, or throat, at the back of the nose and mouth. The pharynx is part of the digestive system as well as the respiratory system because it carries both food and air. At the bottom of the pharynx, this pathway divides in two, one for food (the esophagus, which leads to the stomach) and the other for air. The epiglottis, a small flap of tissue, covers the air-only passage when we swallow, keeping food and liquid from going into the lungs.
The larynx, or voice box, is the uppermost part of the air-only pipe. This short tube contains a pair of vocal cords, which vibrate to make sounds.
The trachea, or windpipe, extends downward from the base of the larynx. It lies partly in the neck and partly in the chest cavity. The walls of the trachea are strengthened by stiff rings of cartilage to keep it open. The trachea is also lined with cilia, which sweep fluids and foreign particles out of the airway so that they stay out of the lungs.
At its bottom end, the trachea divides into left and right air tubes called bronchi, which connect to the lungs. Within the lungs, the bronchi branch into smaller bronchi and even smaller tubes called bronchioles. Bronchioles end in tiny air sacs called alveoli, where the exchange of oxygen and carbon dioxide actually takes place. Each lung houses about 300-400 million alveoli.
The lungs also contain elastic tissues that allow them to inflate and deflate without losing shape and are encased by a thin lining called the pleura. This network of alveoli, bronchioles, and bronchi is known as the bronchial tree.
The chest cavity, or thorax, is the airtight box that houses the bronchial tree, lungs, heart, and other structures. The top and sides of the thorax are formed by the ribs and attached muscles, and the bottom is formed by a large muscle called the diaphragm. The chest walls form a protective cage around the lungs and other contents of the chest cavity.
Separating the chest from the abdomen, the diaphragm plays a lead role in breathing. It moves downward when we breathe in, enlarging the chest cavity and pulling air in through the nose or mouth. When we breathe out, the diaphragm moves upward, forcing the chest cavity to get smaller and pushing the gases in the lungs up and out of the nose and mouth.
The air we breathe is made up of several gases. Oxygen is the most important for keeping us alive because body cells need it for energy and growth. Without oxygen, the body's cells would die.
Carbon dioxide is the waste gas produced when carbon is combined with oxygen as part of the energy-making processes of the body. The lungs and respiratory system allow oxygen in the air to be taken into the body, while also enabling the body to get rid of carbon dioxide in the air breathed out.
Respiration is the set of events that results in the exchange of oxygen from the environment and carbon dioxide from the body's cells. The process of taking air into the lungs is inspiration, or inhalation, and the process of breathing it out is expiration, or exhalation.
Air is inhaled through the mouth or through the nose. Cilia lining the nose and other parts of the upper respiratory tract move back and forth, pushing foreign matter that comes in with air (like dust) either toward the nostrils to be expelled or toward the pharynx. The pharynx passes the foreign matter along to the stomach to eventually be eliminated by the body. As air is inhaled, the mucous membranes of the nose and mouth warm and humidify the air before it enters the lungs.
When you breathe in, the diaphragm moves downward toward the abdomen, and the rib muscles pull the ribs upward and outward. In this way, the volume of the chest cavity is increased. Air pressure in the chest cavity and lungs is reduced, and because gas flows from high pressure to low, air from the environment flows through the nose or mouth into the lungs.
In exhalation, the diaphragm moves upward and the chest wall muscles relax, causing the chest cavity to contract. Air pressure in the lungs rises, so air flows from the lungs and up and out of respiratory system through the nose or mouth.
Every few seconds, with each inhalation, air fills a large portion of the millions of alveoli. In a process called diffusion, oxygen moves from the alveoli to the blood through the capillaries (tiny blood vessels) lining the alveolar walls. Once in the bloodstream, oxygen gets picked up by the hemoglobin in red blood cells. This oxygen-rich blood then flows back to the heart, which pumps it through the arteries to oxygen-hungry tissues throughout the body.
In the tiny capillaries of the body tissues, oxygen is freed from the hemoglobin and moves into the cells. Carbon dioxide, which is produced during the process of diffusion, moves out of these cells into the capillaries, where most of it is dissolved in the plasma of the blood. Blood rich in carbon dioxide then returns to the heart via the veins. From the heart, this blood is pumped to the lungs, where carbon dioxide passes into the alveoli to be exhaled.
The respiratory system is susceptible to a number of diseases, and the lungs are prone to a wide range of disorders caused by pollutants in the air.
The most common problems of the respiratory system are:
Asthma. More than 20 million people in the United States have asthma, and it's the #1 reason that kids frequently miss school. Asthma is a chronic inflammatory lung disease that causes airways to tighten and narrow. Often triggered by irritants in the air such as cigarette smoke, asthma flares involve contraction of the muscles and swelling of the lining of the tiny airways. The resulting narrowing of the airways prevents air from flowing properly, causing wheezing and difficulty breathing, sometimes to the point of being life-threatening. Controlling asthma starts with an asthma management plan, which usually involves avoiding asthma triggers and, sometimes, taking medicines.
Bronchiolitis. Not to be confused with bronchitis, bronchiolitis is an inflammation of the bronchioles, the smallest branches of the bronchial tree. Bronchiolitis affects mostly infants and young children, and can cause wheezing and serious difficulty breathing. It's usually caused by specific viruses in the wintertime, including respiratory syncytial virus (RSV).
Chronic obstructive pulmonary disease (COPD). COPD is a term that describes two lung diseases — emphysema and chronic bronchitis:
Common cold. Caused by more than 200 different viruses that cause inflammation in the upper respiratory tract, the common cold is the most common respiratory infection. Symptoms may include a mild fever, cough, headache, runny nose, sneezing, and sore throat.
Cough. A cough is a symptom of an illness, not an illness itself. There are many different types of cough and many different causes, ranging from not-so-serious to life-threatening. Some of the more common causes affecting kids are the common cold, asthma, sinusitis, seasonal allergies, croup, and pneumonia. Among the most serious causes of cough are tuberculosis (TB) and whooping cough (pertussis).
Cystic fibrosis (CF). Affecting more than 30,000 kids and young adults in the United States, cystic fibrosis is the most common inherited disease affecting the lungs. Affecting primarily the respiratory and digestive systems, CF causes mucus in the body to be abnormally thick and sticky. The mucus can clog the airways in the lungs and make a person more vulnerable to bacterial infections.
Lung cancer. Caused by an abnormal growth of cells in the lungs, lung cancer is a leading cause of death in the United States and is usually caused by smoking cigarettes. It starts in the lining of the bronchi and takes a long time to develop, so it's usually a disease in adults. Symptoms include a lasting cough that may bring up blood, chest pain, hoarseness, and shortness of breath. Radon gas (a gas that occurs in soil and rocks) exposure also might cause lung cancer. Radon is more likely to happen in certain parts of the United States. You can check your home's radon level with a radon kit available at your local home supply or hardware store.
Pneumonia. This inflammation of the lungs usually happens because of bacterial or viral infection. Pneumonia causes fever and inflammation of lung tissue, and makes breathing difficult because the lungs have to work harder to transfer oxygen into the bloodstream and remove carbon dioxide from the blood. Common causes of pneumonia are influenza (the flu) and infection with the bacterium Streptococcus pneumoniae.
Pulmonary hypertension. This is when the blood pressure in the arteries of the lungs is abnormally high, which means the heart has to work harder to pump blood against that high pressure. Pulmonary hypertension may happen in children because of a congenital (present at birth) heart defect or because of a health condition such as HIV infection.
Several respiratory conditions can affect a newborn baby just starting to breathe for the first time. Premature babies are at increased risk for conditions such as:
Although some respiratory diseases can't be prevented, many chronic lung and respiratory illnesses can be prevented by avoiding smoking, staying away from pollutants and irritants, washing hands often to avoid infection, and getting regular medical checkups.
Reviewed by: Steven Dowshen, MD
Date reviewed: July 2015
|National Heart, Lung, and Blood Institute (NHLBI) The NHLBI provides the public with educational resources relating to the treatment of heart, blood vessel, lung, and blood diseases as well as sleep disorders.|
|American Academy of Allergy, Asthma, and Immunology The American Academy of Allergy, Asthma, and Immunology offers up-to-date information and a find-an-allergist search tool.|
|Cystic Fibrosis Foundation This organization offers information about the illness, public policy, clinical trials and local chapters.|
|American College of Allergy, Asthma, and Immunology The ACAAI is an organization of allergists-immunologists and health professionals dedicated to quality patient care. Contact them at: American College of Allergy, Asthma, and Immunology|
85 W. Algonquin Road
Suite 550 Arlington Heights, IL 60005
|American Lung Association The mission of this group is to prevent lung disease and promote lung health. Contact the group at: American Lung Association|
61 Broadway, 6th Floor
NY, NY 10006
|Allergy and Asthma Network/Mothers of Asthmatics (AAN-MA) Through education, advocacy, community outreach, and research, AAN-MA hopes to eliminate suffering and fatalities due to asthma and allergies. AAN-MA offers news, drug recall information, tips, and more for treating allergies and asthma. Call: (800) 878-4403|
|Smoking Stinks! Everyone says smoking is bad for you. Why? Find out in this article for kids.|
|Smoking Smoking is on the decline, but some people are still lighting up. Why? The answer is addiction. Find out more in this article for teens.|
|Croup Croup is characterized by a loud cough that resembles the barking of a seal and difficulty breathing. Most cases of croup are caused by viruses, are mild, and can be treated at home.|
|Bronchitis Bronchitis is an inflammation of the lining of the bronchial tubes. When a person has bronchitis, it may be harder for air to pass in and out of the lungs.|
|Sinusitis Sinus infections, or sinusitis, are common and easily treated.|
|Pneumonia Pneumonia is an infection in a person's lungs. Find out more in this article for kids.|
|Bronchopulmonary Dysplasia (BPD) Babies who are born prematurely or who experience respiratory problems shortly after birth are at risk for bronchopulmonary dysplasia (BPD), sometimes called chronic lung disease.|
|Word! Bronchoconstriction Actually, bronchoconstriction affects the airways in a person's lungs.|
|Cystic Fibrosis Cystic fibrosis (CF) is an inherited disease that causes the body to produce mucus that's extremely thick and sticky. It mainly affects the lungs and the pancreas, causing serious breathing and digestive problems.|
|Asthma Center Asthma means breathing problems. Find out what's going on in the lungs and how to stay healthy, if you have it.|
|Movie: Lungs & Respiratory System Watch this movie about the respiratory system, the system that enables you to breathe.|
|Chilling Out With Colds Cough, sneeze, snort. Those are the sounds of a cold. Find out more about colds in this article for kids.|
|Bronchiolitis Bronchiolitis is a common illness of the respiratory tract caused by an infection that affects tiny airways - the bronchioles - that lead to the lungs.|
|Cystic Fibrosis Cystic fibrosis (CF), a genetic disorder that particularly affects the lungs and digestive system, makes kids who have it more vulnerable to repeated lung infections.|
|Cystic Fibrosis Cystic fibrosis affects the lungs and makes it hard to breathe. Find out more in this article for kids.|
|Kids and Smoking The health risks of tobacco are well known, yet every year many young people take up smoking. Here's how to help your kids avoid tobacco use - or quit, if they've already started.|
|Lungs and Respiratory System Each day you breathe about 20,000 times. Find out more about the lungs and breathing process.|
|Your Lungs & Respiratory System What's something kids are doing all day, every day? Breathing! Your lungs are large and in charge of breathing, so read all about them in this article.|
|Pneumonia Pneumonia is a common lung infection that can usually be treated without a hospital stay.|
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