Respiratory System Functions

  • You breathe. How and why?
  • Can respiration be equated with energy extraction from food?
  • What are dozens of other functions that the respiratory system performs?
  • Is speaking, singing, crying and coughing possible without the respiratory system?
  • As the respiratory disorders are becoming common and severe, how can you prevent the collapse of lungs?

Here, in addition to the respiratory system functions, you’ll also learn about its mechanics, parts, anatomy, diseases with remedies and fun facts.

What is Respiratory System?

With the two new found organs, the mesentery and the interstitium, your body has nearly 80 organs and around a dozen organ systems, including the respiratory, the lymphatic, the nervous, the cardiovascular, the reproductive, the digestive, the excretory and the endocrine. The respiratory system is comprised of a group of closely related organs which work in coordination with one another for the successful execution of respiratory functions.

Respiration is not all about inhalation and exhalation, it does a lot more of incredible significance even to the remotest cells and organs or parts of the body. Actually, there is a close link between breathing and energy. The food you eat has energy locked up in it which is released in the presence of oxygen. So, it can be said that respiratory system plays an important role in the provision of energy or a source of life to every individual cell. Do you know the process of thinking also needs energy?[1]

Your respiratory system consists of many parts. Its parts start from the nose and end at the diaphragm with the pharynx, the larynx, trachea, bronchi, bronchioles, and lungs coming on the way. As the air can be inhaled through the mouth, the oral cavity also plays a part in the process of respiration.[2]

On the other hand, if hemoglobin (the oxygen carrier protein) is also considered as a part of the respiratory system, then this system spreads across every nook and corner of the body.

As it is the source of energy (or life) for every individual cell in the body, you need to maintain good health of the respiratory system through proper diet, regular exercise and breathing in a healthy atmosphere.

Any condition affecting nose, mouth, pharynx, larynx, trachea, bronchi, lungs or diaphragm can be considered as the respiratory system disorder.

Respiratory System Functions

Generally, and mistakenly, breathing is regarded as the only function of the respiratory system. In fact, in addition to breathing, the respiratory organs coordinate with one another to performs a plethora of tasks. Did you ever think that the acts, like speaking, laughing, moving, singing, crying, sneezing and coughing cannot be accomplished without the help of the respiratory organs?

Some of the key respiratory system functions are briefly discussed as under:

Supply of Oxygen & Removal of Carbon Dioxide

While oxygen helps in the extraction of energy from food, carbon dioxide is a gas which the body cells give off as a waste. Accumulation of too much carbon dioxide is poisonous to your body. So, it should be removed.

The supply of oxygen and removal of carbon dioxide takes place between the lungs and the blood. So, it is one of the important respiratory system functions which occurs through blood capillaries. In fact, numerous blood capillaries are found in the alveoli which facilitate this process.

Filtration & Cleaning of Air

The inhaled air may also contain dirt particles, germs, and other harmful substances which may damage your lungs. The hair-like growths called cilia, filter and clean the air by trapping these substances. The trapped particles are expelled upward along the lumen of the respiratory tract for their removal outside the body.

The cilia move the mucus upward toward your mouth and nose. The mucus is removed out of the body through sneezing or it is coughed out.[3]

External Respiration

This is the process by which gases travel between the lungs and the bloodstream. It supplies oxygen from the lungs to the blood which then carries it to all other parts of the body.

Similarly, carbon dioxide travels from the blood to the lungs for exhalation. In this way, external respiration maintains the levels of oxygen in the blood and removes carbon dioxide promptly.

Internal Respiration

This process involves the exchange of oxygen and carbon dioxide between the bloodstream and various tissues of the body. In this way, there is a constant supply of fresh oxygen to the body tissues. At the same time, carbon dioxide goes out of the body.

Warming & Moistening of Air

The respiratory tract begins at the level of nose or mouth and moves downward to reach lungs. During the process of inhalation, air passes through the nasal cavity, pharynx, larynx and trachea, where it gets warmed and moistened.[4]


Speaking is the most advanced form of communication. The organs of speech need the help of lungs for the production of speech sounds. It can be said that the respiratory system is also responsible for the act of speaking.[5]


Just hold your breath and try to smile and laugh. You will be able to smile but not laugh. Smiling is the function of lips while laughing requires the expansion and contraction (tightening) of lungs. So, laughing is also one of the functions of the respiratory system.[6]


For moving any parts or organs of the body, you need energy which comes from the food. Energy can be extracted from food in the presence of oxygen and oxygen is provided by respiration. Therefore, movement is owed to the functioning of respiratory organs. [7]


Singing involves the production of sound which comes from the vibration of vocal cords in the larynx or voice box. The vocal cords vibrate as air passes across them during inhalation or exhalation. It means, singing cannot be accomplished in the absence of the respiratory system.[8]


Sneezing helps remove the dirt trapped in the nose and the respiratory tract. When you sneeze, air coming from the lungs quickly passes through the nose and the mouth. So, sneezing is also one of the respiratory system functions. [9]


When something wrongly enters the trachea or windpipe, you need to cough to remove it. During coughing, air coming from the major respiratory organs (lungs) is quickly released through mouth. Therefore, it can be said that the act of coughing is also owed to the presence of respiratory system.[10]


Can you cry without producing sounds? If so, it won’t be called crying. If crying involves making loud sounds, it should be an act associated with inhalation and exhalation. In other words, your respiratory system is also involved in the act of crying.[11]


Ventilation is one of the physiological functions of the respiratory tract. It involves inspiration for the procurement of air from the external environment to supply the alveoli or the respiratory units. After the extraction of oxygen from it, the remainder gases of the inhaled air are returned to the outside of the body via expiration.The processes of inspiration and expiration require pressure differentials which are owed to the elastic nature of the lungs and chest wall. [12]


Perfusion or pulmonary perfusion refers to the act of actual blood flow through the pulmonary circulation. The right ventricle of the heart pumps the blood into the lungs with the help of the pulmonary artery. On reaching the lungs, the artery divides itself into the left and right branches to supply blood to both the lungs. Afterwards, there is further division of these two branches so that blood can be supplied to all parts of each lung.[13]

It is the adequate ventilation-perfusion ratio which can ensure the adequate exchanges of respiratory gases. Change in gravity, pulmonary artery pressure and alveolar pressure may bring alterations in perfusion. Similarly, ventilation is altered by changes in gravity, blockages in airways and local changes in compliance. [14]

Normal ratio, low ratio (called shunt), high ratio (called dead space) and the absence of ventilation and perfusion (called silent unit) are the possible ventilation-perfusion states in the lungs. The imbalance of ventilation-perfusion causes the shunting of blood which may lead to hypoxia or low level of cellular oxygen. The shunting of blood occurs when there is adequate perfusion but inadequate ventilation.[15]


Diffusion is another major physiological responsibility of the respiratory tract. Carbon monoxide is usually used for the measurement of the diffusion capacity of the lungs. The diffusion capacity for carbon monoxide tests how well the gas in the inhaled air can pass through the wall of an alveolus and enter the capillary. It involves the crossing of the Type 1 alveolar epithelial cells, the interstitial space as well as the vascular endothelial cells.[16]


Olfaction is yet another function of the respiratory system.It is related to the sense of smell. Olfactory fibers are present in the nasal cavity which detect smell when air passes through the cavity.

The process of smell is important for detecting potentially toxic substances. Alternatively, pleasant smells refresh the senses. Therefore, smelling is an important role of the respiratory system.

How Respiratory System Works

The working of your respiratory system not only depends on the healthy functioning and coordination among all the respiratory system organs but also the timely assistance of the associated systems, particularly the pulmonary circulation and the central nervous system. Meanwhile, the respiratory system is also linked to your brain, heart and even the muscles and bones.[17]

Control Center

A brain is the control center for execution and regulation of all the body functions, including respiration. There are respiratory centers in the brain which control the rhythm of breathing (inhalation and exhalation).

The phrenic nerve is responsible for the excitation of the respiratory muscles in a cyclic manner. The pons and the medulla oblongata contain control centers for inspiration and expiration. After determining the metabolic demands of the body, these centers ensure the appropriate rate and depth of ventilation.[18]

In the lower pons, there is the apneustic center which stimulates the center for inspiration in the medulla oblongata for the deep and prolonged inspiration. The pattern of respiration is to be controlled by the pneumotaxic center present in the upper cons.

The control and regulation of the respiratory system functions by the brain is assisted by several groups of the receptor sites. [19]

Air Movement Through the Respiratory Tract

Initiating the process of respiration, the air enters the nasal and oral cavities which are located at the anteriormost end of the respiratory tract. Then it enters the pharynx (throat) and is pushed down to trachea (windpipe) through the larynx (voice organ). Finally, the air enters the lungs and reaches the tiny air sacs, called the alveoli. The exchange of respiratory gases takes place at this point.

Gaseous Exchange at Lungs & Cellular Level

The exchange of respiratory gases takes place at two points, firstly, at the lungs level and, secondly, at the cellular level. In the lungs, oxygen enters the blood and carbon dioxide leaves for its removal out of the body. As the inhaled air reaches the alveoli in the lungs, the Type 1 epithelial cells allow for the exchange of gases. Millions of alveoli create a total surface area of about 130 square feet. Furthermore, embedded among the blood capillaries, these alveoli create an air-blood interface.[20]

At the cellular level, oxygen is diffused into the tissue cells from the blood. At the same time, carbon dioxide diffuses to the blood from the tissues. As a waste product, carbon dioxide is transported to the lungs for excretion.[21]

It is necessary to maintain a constant supply of oxygen and removes carbon dioxide. This happens through the exchange of these gases between the body and the environment.

Externally, an exchange takes places through the nasal and oral cavities. Internally, this exchange occurs between the lungs and the bloodstream.

Purification of Inhaled Air

It is essential to filter the air before it reaches the lungs. Any dust particles or possible toxins are to be removed as they can damage the lungs. This filtering process takes place in the nasal cavity as well as the trachea and the bronchia.

These components of the respiratory system have a lining of cilia and mucous which trap dust and other small particles for their removal out of the body.

Respiratory System Parts (Anatomy)

Do you really know what are the organs or parts of the respiratory system? Is this system comprised of nose, mouth, pharynx, larynx, trachea, bronchi and lungs only? If your answer to the second question is “yes”, you may not be having complete knowledge of respiration.

The organs of the body, like the nose, the mouth, the pharynx, the trachea, the bronchi and the lungs are actually the components of the respiratory tract. Otherwise, in addition to the respiratory tract, the elements of your respiratory system also include the chest wall, the pulmonary circulation, and the central nervous system.[22]

parts of respiratory system

The Naso-oropharynx, conducting airways, respiratory bronchioles and alveoli are the four distinct segments of the respiratory system. On the other hand, the lungs can be divided into the units of respiration and the conducting airways. Here the conducting airways include the trachea, the bronchi and the bronchioles, which facilitate the transport of air from the outside world into the respiratory units, that is, the alveoli.[23]

  • Nostrils: A nostril is either of the two openings of the nose or the nasal cavity that admits air to the lungs. Nostrils are located externally at the anteriormost end of the respiratory tract. They allow the passage of the inhaled air into the air passageways and exit of the exhaled air outside the body.
  • Nasal & Mouth Cavities: The cavities formed by the nose and mouth are called the nasal cavity and the mouth cavity, respectively.

Do you know your nose is just like the door to your respiratory system? The mouth can also serve the same job, but most of the air that you breathe goes in through the nose or nasal cavity. On the other hand, the mouth or mouth cavity is just like an emergency entrance. You use the mouth cavity for breathing when the nose is clogged (blocked) or when you need some extra air.

It is better to breathe through the nose than through the mouth. Do you know why? It is because, lined by hair, cilia, and mucus, the nasal cavity offers a three-fold defense system against the possible entry of dust, dirt, germs, poisons and other harmful particles. These harmful substances and germs are removed out of the body as you sneeze or cough out the mucus.[24]

  • Pharynx: The respiratory tract is divided into the upper and lower segments, called the upper respiratory tract and the lower respiratory tract, respectively. The pharynx or throat is a part of the upper segment. It serves as a common passageway for both the food and air. Obviously, in the respiratory role, it serves as a passageway for air, flowing from mouth to the lung and vice versa.

The pharynx has got a tube-like structure which connects the oral and nasal cavities to the larynx. It can be divided into three distinct regions, namely, the nasal, oral and laryngeal. The nasopharynx segment is found above the soft palate and posterior to the nose. Connected with oral cavity, the oropharynx accommodates the Palatine (faucial) tonsils. The third segment of laryngopharynx extends from hyoid bone and reaches the cricoid cartilage. [25]

Glottis & Epiglottis

Though not contributing much to the structure of the respiratory tract (upper segment), the glottis performs an important role in the production of speech. According to Brunner et al (2010), the glottis is the opening between the vocal cords in the voice organ (larynx).

On the other hand, the epiglottis functions as a covering or lid over the glottis. This valve flap of cartilage covers the opening to the larynx during the act of swallowing. In the absence of this covering, the food would enter the larynx to reach the lungs and cause infection.[26]


Forming an important structural component of the respiratory tract, the larynx also plays an important role in the production of speech sounds. That is why it is also called the voice organ, the voice box or sound apparatus of your body.

This cartilaginous structure lined with epithelium serves as a connection between the throat (pharynx) and the windpipe (trachea). As the very name suggests, the major function of the vocal organ is vocalization or the production of sound. Another function of the organ is to protect the lower airway from the harmful foreign particles. Meanwhile, it also facilitates coughing.[27]


Also called windpipe, the trachea is a tubular structure lying posterior to the esophagus and extending from the larynx to the lungs or bronchi. It is made up of the smooth muscle and C-shaped rings of cartilage are present at regular intervals. On the posterior surface, these cartilaginous rings are incomplete. They render firmness to the tracheal wall and prevent the organ from collapsing.[28]


At its lower end, the trachea divides to form left and right bronchi. These bronchi connect the left and right lungs with the trachea. Within each of the lobes of lungs, there are further divisions of the bronchi. Firstly, you will come across the lobular bronchi. The left and right lungs have two and three lobular bronchi, respectively.[29]


The lungs are the major respiratory organs. They are two in number, the left and right lungs, and are connected with trachea through the bronchi.

Resembling a large balloon, each lung is roughly shaped like a cone. However, it is not filled with air like a balloon. Each lung is packed with a large number of alveoli filled with air. There are over 300 million alveoli in each lung and, grouped together, they look like the bunches of grapes.[30]

If spread out, the lung’s alveoli would cover an area about the size of a tennis court. On the other hand, in the absence of these tiny air sacs, the surface area of the lungs would be just 5 to 6 square feet.[31]

The lungs are located in the thoracic cavity within the chest region. The lungs and the heart are encircled by 24 bones of the rib cage which protect these delicate organs from the outside forces.

There are three lobes in the right lung while the left lung has only two lobes. The left lung is a bit smaller to create room for the accommodation of the heart. [32]

A waterproof and airtight sac, called pleura, encloses both the lungs. Surrounding the membranes of the pleura, there is a fluid which keeps them moist and reduces the risk of abrasive damage.

The lymph nodes not only help in the drainage of the lungs but also assist in fighting diseases. With exposure to smoke, the pink colored tissues of the lungs are turned black.[33]


The diaphragm is a large sheet of muscle that lies at the bottom of the chest. Like other muscles, it acts like a workhorse to power the respiratory system. On receiving a signal from the brain, the diaphragm muscle tightens to expand the lungs room for inhalation. On the other hand, the relaxation of this muscle facilitates exhalation.

Working in coordination with the muscles in the chest wall, it moves the rib cage up or down to force the air into or out of the lungs. Like a bellows, the lungs are filled with air on the opening of the rib cage and the air is expelled on the contraction of the rib cage. When you are breathing rapidly, the abdominal muscles also contract so that more air can be forced out of the lungs.

The muscular layer of diaphragm separates the lungs from the abdominal region. Meanwhile, it also serves as another layer of protection for the major respiratory organs, the lungs. [34]

Central Nervous System

Do you think the central nervous system should be an element of the respiratory system? Mintz (2007), in his book “Disorders of the respiratory tract: common challenges in primary care” regards the central nervous system as an element of the respiratory system. Logically, there must be some control center for the proper execution of respiration and associated functions.

According to Brunner et al (2010), in the resting state, respiration occurs when the phrenic nerve excites the respiratory muscles in a cyclic manner. There are respiratory centers in the brain which control the rhythm of breathing. The control centers for inspiration and expiration are located in the medulla oblongata and pons. They control not only the rate but also the depth of ventilation in order to meet the metabolic demands of the body.

For deep and prolonged inspiration, the inspiratory medullary center is stimulated by the apneustic center in the lower region of the pons. On the other hand, the pattern of respiration is controlled by the pneumotaxic center located in the upper cons.[35]

Pulmonary Circulation

Like the central nervous system, the pulmonary segment of the blood circulatory system also forms an essential element of the respiratory system (Mintz, 2007). Pulmonary circulation is concerned with the supply of blood to the lungs for the purpose of its oxygenation or enrichment with oxygen.

In the pulmonary circulation, deoxygenated blood is pumped to the lungs by the right ventricle of the heart through the passageway of the pulmonary artery. Here it is also noteworthy that the pulmonary artery is the only artery in the body which transports deoxygenated blood. Otherwise, the arteries contain oxygenated blood.

As it reaches the lungs, the pulmonary artery undergoes division into the left bronchus and the right bronchus which supply blood to both the lungs. There is a further branching of the bronchi, so that blood can be supplied to all the parts of each lung.

Around 2% of the blood that the right ventricle pumps to the lungs does not perfuse the alveolar capillaries. It is called the shunted blood which is drained into the left side of your heart without participation in gaseous exchange at the alveolar level.[36]

Respiratory System Diseases

Your respiratory tract has a remarkable defense system to protect the respiratory organs against several potential hazards you breathe in every day. But this defense system is sometimes overwhelmed by the harmful microorganisms, like bacteria and viruses, to cause a respiratory infection.

The respiratory system diseases can be categorized as respiratory infections, cancers, obstructive diseases of the lungs, sleep apnea, pulmonary embolism, interstitial lung disease, and other conditions.

Some of the commonly occurring respiratory system conditions are being described asunder with the symptoms, diagnosis, and treatment.

Acute Bronchitis

One of the infectious diseases of the respiratory system, acute bronchitis refers to the swelling of the bronchi that connect the trachea with the left and right lungs. In results in the inflammation and plugging of the airways with mucus.

Acute bronchitis may be caused by a viral infection or the air pollutants, like dust, smoke, and chemical fumes. The risk of this disease increases in the cigarette smokers, and those suffering from obstructive lung disease and heart failure.[37]

Acute-Bronchitis image


The acute bronchitis symptoms include:

  • A persistent cough producing green, yellowish or gray phlegm is a predominant symptom of acute bronchitis.
  • Other symptoms include a sore throat, fever, and headache.
  • Chest pain may be caused by the severe coughing bouts.
  • Meanwhile, the individuals suffering from acute bronchitis may also experience wheezing and difficulty in breathing.

The symptoms of this respiratory system disorder may disappear on their own in a week in the healthy adults.[38]


Usually, there is no treatment for the condition of acute bronchitis. However, the patients are advised to stop smoking immediately. In some cases, the medications like dextromethorphan syrup and an albuterol inhaler are recommended but they fail to have any effect if the causative agent is a virus. If a viral infection is accompanied by a bacterial infection, the use of antibiotics becomes mandatory.[39]

To quit smoking is the most important thing that you should do as a preventive measure for acute bronchitis. If you frequently wash your hands after coming in contact with the infected people, the chances of picking up a cold virus shall be reduced. Meanwhile, you also need to avoid touching your eyes and nose.


Commonly known as flu, influenza is an acute infection of the upper respiratory tract. The outbreaks of flu occur with the onset of winter and may last up to three months. Around 10 to 20% population is usually affected by this disorder. If you are already suffering from asthma or chronic obstructive pulmonary disease, influenza may worsen the symptoms of these obstructive diseases. The flu virus is also likely to cause pneumonia.

Flu is caused by a viral infection. Among different types of flu viruses, influenza A is responsible for most of the outbreaks of disease. It causes more severe symptoms and results in more deaths than either B or C types.


Individuals suffering from flu may complain of following things:

  • Fever, headache, and pain in muscles.
  • A cough, sore throat and chills.
  • Patients may also feel weakness.

The influenza symptoms usually last for two to seven days. For diagnosis, your health care provider will look for the symptom prescribed for flu. An outbreak of influenza in the community may also indicate the likelihood of the disease.


Drinking lots of fluids and getting plenty of rest are considered as the watchword for surviving flu. The symptoms may be reduced by the use of over-the-counter drugs, like pain relievers, antihistamine, and decongestants. In case a bacterial infection complicates the flu, your healthcare provider may prescribe some antibiotics but they will have no effect on the influenza virus itself.

If taken shortly after the symptoms begin, certain prescription medications, like amantadine and rimantadine, may reduce the symptoms by about half.

Recently, two effective antiviral therapies have been developed, i.e. oseltamivir and zanamivir. The former is an oral medication while the latter is inhaled. Oseltamivir is considered as the most effective drug for the treatment of avian flu.[40]


Asthma, or bronchial asthma, is a chronic lung disorder and, as you know, a chronic condition has no permanent cure. However, it is not a contagious disease which means you cannot catch it from someone who is suffering from it. It can be mild or severe but you can control it with an adequate understanding of the condition.

Asthma image

This irritating disease affects breathing and makes the patients unable to breathe normally. The attacks can be as often as many times a day or as infrequent as once in a month.[41]

Asthma is characterized by the occasional or varying tightening of the air passages, thus posing difficulty in breathing. Bronchial asthma and cardiac asthma are two different types of asthma. In case of cardiac asthma, the air sacs are filled with fluid and cause breathing problems. On the other hand, bronchial asthma involves the narrowing of the breathing tubes and the inhaled air has difficulty in reaching the air sacs or alveoli.[42]


The frequently occurring asthma symptoms are listed below:

  • Shortness of breath due to narrowing of the breathing tubes.
  • Coughing and wheezing. (In case of viral infection, the patients continue coughing and/or wheezing for over 6 weeks.)
  • Symptoms of cold which may go on for weeks may arise due to asthma.
  • Worsening of coughing or wheezing by exercise or laughing.
  • Feeling ill quite quickly.
  • Having temperature or fever accompanied by a runny nose.

Coughing up greenish, thick and sticky phlegm.[43]


Non-medicine treatments, medications, and complementary therapies are available for the treatment of asthma. In case of non-medicine treatment, the patients are advised to avoid contact with allergens which may trigger their asthma, such as house dust mites. The use of allergy-reducing products may also be recommended by the asthma specialists.

When the non-medicine treatments do not prove to be effective, you need to try usual medicines or complementary therapies. The available complementary therapies include acupuncture, homeopathy, hypnosis and breathing exercises, such as Buteyko and yoga.[44]

The traditional medicine systems of Pakistan and India use the Datura plants for the cure of asthma. The substances present in Datura plants are useful in relieving the symptoms of the disease. A medicine developed from this plant, called atropine, can dry up the secretions.

In Traditional Chinese Medicine, the ephedra (Ma Huang) remedy is used. But ephedrine (adrenaline) in ephedra involves a lot of side effects. The traditional Japanese medicine system (Kanpo) also makes use of ephedra for the treatment of asthma.[45]

Respiratory System Facts

  1. Do you know you breathe over 10 million times a year with the heart beating tirelessly around 100,000 times a day?[46]
  2. While passing through respiratory passageways, the inner layers of gas particles move faster than the outer ones.[47]
  3. There is a close link between energy and breathing. Actually, when you breathe air, the oxygen gas in it lets the energy out which is locked up in the food.[48]
  4. The process of inspiration and expiration could not be completed if the lungs and the chest wall were not of elastic nature.[49]
  5. In the absence of the respiratory system, you won’t be able to live more than a few minutes.[50]
  6. According to Brunner et al (2010), in the early to middle adulthood, there begins a gradual decline in the functioning of respiratory system. It also affects the respiratory structures.[51]
  7. The process of respiration starts as soon as you are born and it keeps on working until you die, never taking a short break.[52]
  8. Your body cells and tissues are constantly wearing out and being replaced without your even knowing about this fact.[53]
  9. Spanish flu, a disorder of the respiratory system, has become unknown except in the history books. This epidemic of 1918-19 claimed the lives of 20 to 40 million people worldwide near the end of the First World War.[54]
  10. Interestingly, a single human cell contains as many as 3 billion letters of the coded instructions that the genome represents![55]
  11. It is not just breathing, the acts like coughing, sneezing, laughing, speaking, moving, crying and singing are allowed to the functioning of respiratory organs.[56]
  12. Do you know breathing through the nose is healthier than breathing through the mouth? It is because the nose filters and cleans the air.[57]
  13. You breathe in over 7,950 liters (2,100 gallons) of air every day![58]
  14. In a healthy nose, the cilia may move back and forth around 14 to 16 times/second.[59]
  15. It is just a myth that if people do not spend much time outdoors, they can be safe from air pollution. The reality is the reverse of it.[60]
  16. The findings of American Lung Association show that the indoor air may be more polluted than the outdoor air. It is due to poor ventilation of homes. [61]
  17. The surface area of the lungs is so large that you can compare its size to a tennis court.[62]
  18. Our lungs are not symmetrical. The left lung is smaller in size than the right lung. This is so that the heart can have sufficient room in the chest cavity.
  19. People who are habitual of breathing through the mouth can end up with crooked teeth. This is because breathing through the oral cavity can cause the jaws to shrink in size.
  20. The lungs are the only organs of the body which can float on the surface of the water. This is because each lung contains millions of alveoli containing air.
  21. The process of respiration produces carbon dioxide and vapors of water as byproducts.
  22. In humans, the normal rate of breathing usually ranges from 12 to 16 breaths per minute and the usual depth of breathing is about 400 to 500 ml.[63]
  23. In the UK alone, there are around 5 million people suffering from asthma. [64]
  24. As of 2011, around 23 million people in the USA are dealing with asthma.[65]
  25. Do you know 7th child is affected by asthma at any one time? It is the most common chronic condition of the respiratory system affecting children.[66]


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