Thirty Surprising Facts About the Respiratory System
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
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.
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
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
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.
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 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.
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© 2011 Linda Crampton