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Thirty Surprising Facts About the Respiratory System

Updated on August 6, 2017
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Linda Crampton is a teacher with a first class honors degree in biology. She writes about human biology and the scientific basis of disease.

The respiratory system is vital for the input of oxygen and the output of carbon dioxide.
The respiratory system is vital for the input of oxygen and the output of carbon dioxide. | Source

A Vital System

The human body is a fascinating structure that can perform some very impressive feats. In order to perform these feats, the body needs input from the environment and must release the waste products that it makes. The regular input of oxygen and output of carbon dioxide via the respiratory system is vital. This system has some interesting and sometimes surprising features.

The respiratory system is a network of tubes, sacs, and muscles that obtains oxygen from the air and transports it to the bloodstream. The blood delivers the oxygen to all the cells in the body, which use it to produce energy from digested food. Carbon dioxide waste made by the cells is transported in the opposite direction, from the cells into the respiratory system to be exhaled.

We depend on our respiratory system for our survival, since all of our vital organs require oxygen in order to function. Brain cells are damaged after only a few minutes without oxygen (except under very special conditions, such as deep chilling of the body) and death may soon follow.

Breathing and Gas Exchange for Students

Respiration and Breathing: What's the Difference?

Respiration is a multi-step process involving the respiratory system, the circulatory system, and tissue cells. Unfortunately, the word "respiration" is often used instead of "breathing", which can be confusing for a biology student. When it's used in its technical sense, the term respiration refers to more than just breathing.

During respiration, oxygen is inhaled throught the nose and/or mouth and then transported to the tissue cells via the bloodstream. The oxygen participates in a complex chemical reaction inside the cells. This reaction produces energy, carbon dioxide, and water. The carbon dioxide and water are transported to the lungs via the bloodstream and exhaled.

Respiration is often said to involve four processes, as described below. The respiratory system is involved in the first two steps.

  • Breathing (ventilation): the inhalation of oxygen and the exhalation of carbon dioxide
  • External Respiration: gas exchange between the lungs and the bloodstream; oxygen leaves the lungs and goes into the bloodstream while carbon dioxide moves in the opposite direction
  • Internal Respiration: gas exchange between the bloodstream and the tissue cells; oxygen leaves the bloodstream and enters the tissue cells while carbon dioxide moves in the opposite direction
  • Cellular Respiration: a chemical reaction between oxygen and carbohydrates inside the tissue cells

The Bronchial Tree

Plasticized human trachea, bronchi, and bronchioles
Plasticized human trachea, bronchi, and bronchioles | Source

Airways and Alveoli Facts

1. The airways begin with the trachea (windpipe), which branches into two bronchi, one going to each lung. Each bronchus divides repeatedly to form narrower bronchi and then even narrower bronchioles, producing a structure called the bronchial tree.

2. The bronchioles lead to tiny air sacs called alveoli. According to most researchers, an adult lung contains 300 million to 500 million alveoli.

3. The lungs are able to float on water since they contain so many air sacs.

4. If all the alveoli in both lungs were flattened out, they would have a total area of about 160 square meters—about 80% of the size of a singles tennis court and about 80 times greater than the surface area of an average-sized adult’s skin.

5. The interior lining of an alveolus is covered by a thin layer of water. This enables oxygen to move through the wall of the alveolus and into the bloodstream efficiently.

6. Water molecules on the lining of an alveolus are attracted to each other, creating a force known as surface tension. When the alveoli become smaller during exhalation, the surface tension increases. This could cause the alveoli to collapse and prevent them from expanding again.

7. The lining of alveoli produces a substance called a surfactant. The surfactant reduces the surface tension of water, preventing the alveoli from collapsing.

Structure of the lungs
Structure of the lungs | Source

Alveoli, Capillary, and Blood Facts

8. The surface of an alveolus is covered with capillaries. Capillaries are narrow blood vessels with a thin wall that is just one cell thick.

9. Like the wall of capillaries, the wall of an alveolus is also just one cell layer thick. This allows for quick absorption of oxygen from the alveoli into the capillaries and the quick release of carbon dioxide from the capillaries into the alveoli.

10. A red blood cell contains about 250 million hemoglobin molecules, which carry oxygen through the blood. Each hemoglobin molecule can carry four oxygen molecules. There are 4 million to 6 million red blood cells in each microliter (cubic millimeter) of blood.

Lung Anatomy and Function

Lung Facts

11. The right lung is larger than the left one. The heart is located between the lungs with its pointed tip directed towards the left side of the body. The position of the heart allows for less space for the left lung than for the right lung.

12. An adult generally breathes between 12 and 18 times a minute when he or she is not exercising, or about 17,000 to 26,000 times in a twenty-four hour period.

13. The total lung capacity (maximum amount of air that someone’s lungs are capable of holding) is between 4 and 6 liters of air in an adult. Males usually have higher total lung capacities than females.

14. When we are relaxed we inhale and exhale about 500 mL of air per breath. This value is called the tidal volume. We inhale and exhale greater volumes of air in certain situations, such as when we are exercising or during forced breathing.

15. About 30% of the tidal volume of air never reaches the alveoli and stays in the airways. This air is called “dead air” because it's useless for oxygen extraction as it isn’t in the alveoli.

16. Even after a very strong exhalation, about 1000 to 1200 mL of air remains in the lungs. This is known as residual volume.

17. Exhaled air contains water vapor from our bodies. Each day we lose about half a liter of water from our bodies by exhaling.

The Viscera and Parietal Pleura Around the Lungs

The lungs are surrounded by two membranes called the visceral pleura and the parietal pleura. The narrow space between the two membranes is called the pleural cavity and contains a small amount of a lubricating fluid.
The lungs are surrounded by two membranes called the visceral pleura and the parietal pleura. The narrow space between the two membranes is called the pleural cavity and contains a small amount of a lubricating fluid. | Source

Inhalation and Exhalation Facts

18. The diaphragm is a sheet-like muscle under the lungs. The diaphragm and the intercostal muscles between the ribs are both used for inhalation (also called inspiration), but the diaphragm plays a more important role. The diaphragm is curved upwards when relaxed and flattens as it contracts.

19. Inhaled air doesn’t push the lungs open. Instead, during inhalation the diaphragm and intercostal muscles contract, increasing the volume of the chest cavity and pulling the lungs open. Residual air inside the lungs spreads out, causing the air pressure inside the lungs to be reduced. Air outside the body, which is under a higher pressure than the air in the expanded lungs, then moves into the nose and mouth and down the airways towards the lungs.

During exhalation (also called expiration) the diaphragm and intercostal muscles relax, causing the lungs to decrease in volume and air to be pushed out.

20. The medulla oblongata in the brainstem stimulates us to inhale without us having to make a conscious decision.

21. A high level of carbon dioxide in the blood is more important in triggering inhalation than a low level of oxygen.

The medulla oblongata, pons, and midbrain form the brainstem (or brain stem) at the top of the spinal cord. The medulla oblongata stimulates inhalation.
The medulla oblongata, pons, and midbrain form the brainstem (or brain stem) at the top of the spinal cord. The medulla oblongata stimulates inhalation. | Source

Facts About the Passage of Air Through the Airways

22. At the top of the trachea is an enlarged area called the larynx. The larynx is also called the voicebox, since it contains the vocal cords. The vocal cords are also known as the vocal folds. The esophagus transports food to the stomach and starts at the back of the throat behind the trachea. When we swallow, a flap of tissue called the epiglottis moves downwards to cover the trachea to prevent the entry of swallowed materials, which could block the passage of air and cause choking.

23. Mucus is a vital substance made by the air passages. Mucus traps inhaled dirt and bacteria and also moistens the airways.

24. The cells lining the airways have hair-like extensions called cilia. The cilia beat in a coordinated fashion to create a current of mucus that is swept up to the back of the throat, where it's swallowed.

25. Smoking damages cilia, allowing mucus to build up and block the airways.

Mucus and Cilia in the Lungs: An Animation

Sneezing and the Photic Sneeze

26. The fastest speed at which material released by a sneeze travels is often said to be 100 miles an hour. This number became popular a long time ago. Some scientists of today say the speed is hugely exaggerated. A virologist at the Alberta Provincial Laboratory for Public Health found that sneezes travel at only ten miles an hour. He did say that his subjects had a slight build and that the speed might have been higher if subjects with a bigger frame had been used in the experiment, however.

27. Sneezing can be due to other factors besides irritation in the nose. Some people sneeze when entering a bright environment after being in the dark. This type of sneeze is known as a photic sneeze, or a photic sneeze reflex. A reflex doesn't involve a conscious decision by the brain.

28. About 20% to 30% of people are thought to experience photic sneezes. A photic sneeze is also known as the ACHOO syndrome (Autosomal Dominant Compelling Helio-Ophthalmic Outbust Syndrome). Some people sneeze once when exposed to light, but most people sneeze multiple times. There have been reports of photic sneeze outbursts involving forty sneezes. The trait seems to have a genetic basis.

The Trigeminal Nerve and the Photic Sneeze

The branches of the trigeminal nerve (in yellow); this nerve is believed to be involved in the photic sneeze that some people experience when they are suddenly exposed to strong light
The branches of the trigeminal nerve (in yellow); this nerve is believed to be involved in the photic sneeze that some people experience when they are suddenly exposed to strong light | Source

The Cause of Photic Sneezes

29. The nerve that carries signals from the eyes to the brain is called the optic nerve. When the pupils of the eyes are adapted to a dark environment they are dilated. If someone moves from a dark environment to a very bright environment, the optic nerve sends an electrical signal to the brain, causing it to constrict the pupils in order to protect the inside of the eyeball from light damage.

The trigeminal nerve is stimulated when an irritant enters the nose. The nerve sends a message to the brain, which causes a sneeze. The trigeminal nerve lies close to the optic nerve. Scientists think that when photic sneeze sufferers enter a bright environment, some of the electrical signal traveling through the optic nerve to the brain escapes into the trigeminal nerve, causing the person to sneeze.

30. Some cases of migraines and epilepsy may be neurologically linked to photic sneezes.

The respiratory system is an interesting and vital part of our body. Avoiding activities that harm it and taking steps to keep it healthy are important.

A Respiratory System Quiz


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References

Information about the respiratory system from the NIH (National Institutes of Health)

Biology of the lungs and airways from the Merck Manual

Lung anatomy from Medscape

Why we sneeze in bright light from the BBC

Speed of a sneeze from Popular Science

© 2011 Linda Crampton

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    • AliciaC profile image
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      Linda Crampton 9 months ago from British Columbia, Canada

      You're welcome. I'm glad the article helped you.

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      someone 9 months ago

      thanks this is helpful

    • AliciaC profile image
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      Linda Crampton 2 years ago from British Columbia, Canada

      Thank you very much for the kind comment, fpherj48! I love learning about the human body, too. It's a fascinating topic.

    • AliciaC profile image
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      Linda Crampton 2 years ago from British Columbia, Canada

      Thank you very much for the comment and the shares, Patricia! I always appreciate your visits and the beautiful angels that you send.

    • fpherj48 profile image

      Paula 2 years ago from Beautiful Upstate New York

      Alicia....A fabulous teaching hub....So thorough and fascinating to learn such detail and vital information. Thank you for this education. I love learning more about our bodies and health!

    • pstraubie48 profile image

      Patricia Scott 2 years ago from sunny Florida

      Aren't we thankful for our medulla!! ?? Alicia, I thought I knew a thing or two about these amazing respiratory organs that I possess but clearly I had no real clue.

      So much information I had not even realized is true.

      Thank you for taking the time to so carefully share this with us.

      Angels are on the way to you this lovely Sunday afternoon (just had a gentle rain and now the sun is smiling down on us again).

      ps

      Shared pinned

    • AliciaC profile image
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      Linda Crampton 2 years ago from British Columbia, Canada

      Thank you for the interesting comment, Joe Bob!

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      Joe Bob 2 years ago

      This is like, really, like, cool ans stuff dude.

    • AliciaC profile image
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      Linda Crampton 2 years ago from British Columbia, Canada

      Thank you. I appreciate your visit.

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      Wftrctdctdc 2 years ago

      This was good

    • AliciaC profile image
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      Linda Crampton 3 years ago from British Columbia, Canada

      Thank you for the comment, sel.

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      sel 3 years ago

      Cool! Thanks.

    • AliciaC profile image
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      Linda Crampton 4 years ago from British Columbia, Canada

      Thank you very much, America!

    • AliciaC profile image
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      Linda Crampton 4 years ago from British Columbia, Canada

      Thank you, ramani hariharan.

    • profile image

      ramani hariharan 4 years ago

      an interesting hub njoyed

    • AliciaC profile image
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      Linda Crampton 5 years ago from British Columbia, Canada

      I'm glad that the hub was useful!

    • profile image

      ... 5 years ago

      it helped a lot

    • AliciaC profile image
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      Linda Crampton 6 years ago from British Columbia, Canada

      Thanks a lot for the visit and the comment, Koffeeklatch Gals. I think that the human respiratory system is amazing!

    • KoffeeKlatch Gals profile image

      Susan Haze 6 years ago from Sunny Florida

      102.5 mph is quite a powerful sneeze. That's hurricane proportions. Great information - great research. I also didn't know the lungs were pulled open, I awlays thought they opened by breathing in and filling them with air.

    • AliciaC profile image
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      Linda Crampton 6 years ago from British Columbia, Canada

      Thanks for the comment and the vote, Om Paramapoonya!

    • Om Paramapoonya profile image

      Om Paramapoonya 6 years ago

      Thanks for sharing these interesting facts. It was a fun read. Voted useful and up. :)

    • AliciaC profile image
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      Linda Crampton 6 years ago from British Columbia, Canada

      Thank you very much for the comment and vote, Pamela99.

    • Pamela99 profile image

      Pamela Oglesby 6 years ago from United States

      I also found your hub very detailed and accurate. I also studied anatomy and physiology when I was in school and became an RN. I didn't have the great video either. Voted/rated up.

    • AliciaC profile image
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      Linda Crampton 6 years ago from British Columbia, Canada

      Hi, Alternative Prime! Thank you for the comment and rating.

      Thank you as well, b. Malin!

    • b. Malin profile image

      b. Malin 6 years ago

      Having worked for a Heart Specialist for over ten years, I found your Hub on this subject very informative and well written...Wonderful videos as well. You've made it simple for all to understand, our Respiratory Systems.

    • Alternative Prime profile image

      Alternative Prime 6 years ago from > California

      Hi Alicia,

      Interesting and educational at the same time. Thoroughly enjoyed it and rated accordingly.

    • AliciaC profile image
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      Linda Crampton 6 years ago from British Columbia, Canada

      Hi, Peggy W. Thank you very much for the comment and the rating!

    • Peggy W profile image

      Peggy Woods 6 years ago from Houston, Texas

      Back when I was studying anatomy and physiology there was no Internet with terrific videos like the one shown in this hub. You have mixed interesting details into this like #4 which I never heard previously. Makes studying the respiratory system ever so much more interesting! Rated up and useful. Thanks!

    • AliciaC profile image
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      Linda Crampton 6 years ago from British Columbia, Canada

      Thank your for the comment, A.A. Zavala!

      GmaGoldie - Thank you very much for the kind comment. There’s always residual air in the lungs. A small amount of the air forming the residual volume is replaced with freshly inhaled air during each breath, and a small amount of the stale air that was part of the residual volume is exhaled with each breath, so the residual air is slowly but continually being replaced. If we increase the rate of breathing or the depth of the breaths the residual air will be replaced more quickly.

      Fossillady - Thank you for commenting. I am so very sorry about your husband's lung cancer.

    • Fossillady profile image

      Kathi 6 years ago from Saugatuck Michigan

      This was very thorough, good job with it, Alicia! I recently studied the lung system because of my husband's lung cancer. If people paid closer attention to how the body works maybe they could prevent some of the diseases that plague us. Thank you for sharing

    • GmaGoldie profile image

      Kelly Kline Burnett 6 years ago from Madison, Wisconsin

      Fantastic Hub! Very well written and organized. Is it true that exhalation "cleans" the lungs?

    • A.A. Zavala profile image

      Augustine A Zavala 6 years ago from Texas

      I always hated this ssystem on the anatomy test. But the hub made it easy to understand. Thank you for sharing.