99 Fun Facts About Respiratory System

The left lung is the smaller one, to leave room for which organ?

Heart. It sits left of centre and fits into a dent in the left lung called the cardiac notch, so that lung holds less air than its shorter, wider partner.

Which blood cells pick up oxygen in the lungs and carry it to the rest of the body?

Red blood cells. They have no nucleus and no mitochondria, so they burn none of the oxygen they carry and can deliver every bit of it to the tissues.

What is the common name for the trachea?

The windpipe. If the throat above it is blocked, a surgeon can cut a small hole into it at the front of the neck, a tracheostomy, and the patient breathes through a tube there.

Which first-aid technique, named for an American surgeon, uses abdominal thrusts to clear a choking person's airway?

The Heimlich maneuver. Henry Heimlich described it in 1974, and in 2016, aged 96, he said he had used it himself to save a choking woman at his retirement home.

What shape are the cartilage hoops of the trachea?

Incomplete and C-shaped. The gap at the back is bridged by a muscle that tightens during a cough, narrowing the tube to help force the air out.

Where does the trachea end by splitting into the two main bronchi?

At the carina. The lining of this ridge is the most cough-sensitive spot in the airway, so anything that lands on it sets off violent coughing.

Which birds did coal miners carry underground because carbon monoxide knocks them out before it harms a human?

Canaries. Their rapid breathing and small bodies make them succumb first, which gave miners time to get out; Britain only decided to replace its pit canaries with electronic detectors in 1986.

If a foreign body is inhaled, where does it usually lodge?

Right main bronchus. It is wider, shorter and more upright than the left one, so an inhaled peanut or bead usually drops straight into it.

Approximately how many alveoli does a typical pair of human lungs contain?

About 480 million. That is an average: counts in six adult lungs ran from 274 to 790 million, because bigger lungs hold more alveoli rather than bigger ones.

The word 'alveolus' comes from Latin meaning what?

Little cavity. English borrowed the word in 1706 for a tooth socket and only later extended it to the lung's air sacs, which is why dentists still talk about alveolar bone.

Which alveolar cells release pulmonary surfactant?

Type II. They cover only a few percent of the alveolar wall, the rest being flat type I cells, yet without their secretion the air sacs would collapse with every breath out.

What does pulmonary surfactant do to the fluid lining the alveoli?

Reduces its surface tension. Water in the lining clings to itself and resists stretching, so without this slick coating the wet air sacs would be far harder to inflate.

Insufficient surfactant in preterm babies causes which condition?

Infant respiratory distress syndrome. Doctors now deliver replacement surfactant straight into the baby's airway, and steroids given to the mother before an early birth speed up the lungs' own supply.

What is the larynx commonly called?

The voice box. Rest a finger on the front of your neck and swallow: you will feel it ride upward, a lift that helps close off the airway while food goes past.

A boy's voice breaks and deepens at puberty because his vocal cords do what?

Lengthen and thicken. Like a thicker rubber band, longer and heavier cords give a deeper note, and the cracks and squeaks come while the body adjusts to their new size.

Which laryngeal cartilage forms the Adam's apple?

Thyroid. The name is Greek for 'shield-shaped', and this shield grows and juts forward at puberty under testosterone, which is why the bump usually shows more on a man's neck.

Which leaf-shaped flap stops food and water entering the trachea?

The epiglottis. It stands upright while you breathe, then folds back over the airway as the throat lifts during a swallow, steering the mouthful toward the stomach instead.

Pertussis is the medical name for which childhood infection, known for the gasp for air that ends each attack?

Whooping cough. The 'whoop' is the sound of a child dragging air back in after a long bout of coughing, and the illness lingers so long it is also called the 100-day cough.

Which lumps of tissue behind the nose, often removed in childhood, are formally called the pharyngeal tonsils?

The adenoids. They swell through early childhood, when they can block the nose and force a child to breathe through the mouth, then shrink away and have usually vanished by adulthood.

Which passage links the middle ear to the back of the nose?

The auditory tube. Better known as the Eustachian tube, it stays shut until a swallow or yawn opens it for a moment to even out the air pressure, and that is the pop you feel on a plane.

Which nerve, formed from roots C3 to C5, supplies the main breathing muscle?

The phrenic. Irritate it and you get stubborn hiccups; lose both sides, as a high spinal injury can cause, and a person may need a ventilator to breathe.

During inhalation, which way does the main breathing muscle move as it contracts?

Downward toward the abdomen. As the dome flattens, the chest cavity grows and the pressure inside drops below that of the air outside, so air flows in to fill the lungs.

A hiatus hernia is when part of the stomach pushes through which structure?

The diaphragm. The stomach squeezes up through the hiatus, the opening that normally lets the food pipe through, and the bulge lets acid escape upward, which is why heartburn is the classic symptom.

Which disorder makes breathing stop and restart again and again through the night, often with loud snoring?

Sleep apnea. The airway closes or blocks until the sleeper restarts with a snort or gasp, and in bad cases that happens 30 or more times an hour.

For how many years did Guinness record-holder Charles Osborne have hiccups?

68 years. They started in 1922 as he handled a hog for slaughter and stopped one morning in 1990; in between he married twice and fathered eight children.

What is the scientific name for a hiccup?

Singultus. The Latin word means a sob: a jerk of the main breathing muscle sucks air in, and the throat snaps shut on it a split second later to make the 'hic'.

What is a pneumothorax, in which leaked air builds up inside the chest, more commonly called?

A collapsed lung. The escaped air presses on the lung from outside so it cannot fully expand; it can strike with no injury at all, and tall, thin people and smokers are more at risk.

ACHOO syndrome makes some people sneeze the moment they step out into what?

Bright sunlight. Aristotle blamed the sun's heat on the nose, but Francis Bacon faced the sun with his eyes shut and did not sneeze, which pointed to the eyes; doctors call it the photic sneeze reflex.

What is the fluid-lined space between the two membranes that wrap each lung called?

The pleural cavity. Its thin film of fluid lets the lungs glide as you breathe, and when the membranes inflame and rub instead, every breath brings the sharp pain of pleurisy.

Which layer of the lung's double membrane covers the lung itself?

Visceral. This inner layer has no pain nerves, so the stabbing ache of an inflamed chest lining comes from the outer layer that lines the ribs.

What is the half-litre of air moved by each quiet breath called?

Tidal volume. Intensive-care ventilators are set by it, and a landmark trial found that giving smaller breaths than tradition dictated saved lives by sparing fragile lungs from overstretching.

What is the part of each breath that never reaches the alveoli called?

Dead space. A snorkel adds to it, since every breath in begins with the stale air left in the tube from the last breath out.

Where in the brain are the respiratory centres that control breathing in mammals?

The medulla and pons. They fire on their own, which keeps you breathing in your sleep, and it is by quieting these centres that an opioid overdose slows breathing until it stops.

The urge to breathe is driven mainly by a build-up of which gas in the blood, rather than by falling oxygen?

Carbon dioxide. Sensors in the brain and in the big arteries of the neck and chest track its level closely, and a rise makes you breathe faster and deeper.

Which gas makes up about 78 percent of each breath in and is breathed back out unused?

Nitrogen. Its atoms are bonded so tightly that the body cannot use the gas at all; the nitrogen in our proteins comes from food, not from the air we breathe.

In hemoglobin, each oxygen molecule binds to an atom of which metal?

Iron. Each hemoglobin molecule holds four atoms of it, one for each oxygen molecule it carries, whereas horseshoe crabs carry their oxygen with copper instead, which is why their blood is blue.

Which inherited disease, which clogs the lungs with thick, sticky mucus, also makes a child's sweat unusually salty?

Cystic fibrosis. It disrupts the glands that make both mucus and sweat, so doctors confirm it with a sweat test: an unusually high level of salt is the telltale sign.

Which breathing condition takes its name from the Greek word for panting?

Asthma. The name fits an attack, when the airways inflame and narrow until the sufferer wheezes and has to fight for every breath.

Which fireproof mineral, once packed into buildings and ships, can cause lung cancers decades after its dust is inhaled?

Asbestos. Its thin fibres lodge in the lungs and stay there, and the diseases they cause, including the cancer mesothelioma, can take 10 to 40 years or more to show.

Which infection did the physician William Osler call 'the captain of the men of death'?

Pneumonia. He meant it had become one of the great killers of his day, yet he also called it 'the friend of the aged', because it gave the frail a quick and often painless end.

Which German doctor announced in 1882 that he had found the bacterium that causes tuberculosis?

Robert Koch. The day he announced it, 24 March, is still World Tuberculosis Day, but the cure he later promoted, tuberculin, was a failure that survives only as a skin test for the infection.

By what historical name was tuberculosis widely known in the 1800s?

Consumption. The name described how the illness seemed to consume its victims from within, as they grew thinner and weaker over months or years.

The BCG vaccine against tuberculosis was bred from a weakened strain of a germ that infects which animals?

Cattle. Albert Calmette and Camille Guérin regrew the bovine germ 230 times over 13 years until it could no longer cause disease, and the vaccine still carries their initials.

What fraction of the world's people does the WHO estimate has been infected with TB bacteria?

One in four. Most of them will never fall ill: only about 5 to 10 percent of infected people go on to develop the disease itself.

In spirometry, what does FEV1 measure?

Air forcibly blown out in the first second. Healthy lungs empty most of their air in that second, so a low share of the total is the telltale sign of narrowed airways, as in COPD.

Which hair-like structures line the airways and beat in waves to sweep mucus up and out of the lungs?

Cilia. They beat in coordinated waves that carry dust-laden mucus up to the throat like a slow escalator, where it is quietly swallowed.

Which breathing organs do zoologists call branchiae, as in 'nudibranch'?

Gills. 'Nudibranch' means naked gills, because these sea slugs have no shell as adults and many of them breathe through feathery plumes exposed on their backs.

In which reptiles is one lung usually tiny or missing, leaving the other to do the breathing?

Snakes. A tube-shaped body needs long, thin organs, so in most species the left lung is a shrunken leftover or gone altogether.

The adult human lungs' gas-exchange surface is often compared to the size of what?

A tennis court. The textbook comparison is generous: estimates run from about 50 to 75 square metres, which is less than half the area of a singles court.

Which medical instrument began in 1816 as a sheaf of paper rolled into a tube by René Laennec?

The stethoscope spared Laennec the embarrassment of pressing his ear to a woman's chest. His first purpose-built model was a hollow wooden cylinder about 25 cm long.

Which gas makes a voice squeaky because sound moves through it nearly three times faster than in air?

Helium leaves the pitch of the vocal folds unchanged; it raises the resonances of the vocal tract, so only the timbre shifts. Inhaled to excess it is dangerous, because it displaces the oxygen the body needs.

Which French naval officer and ocean filmmaker co-invented the Aqua-Lung with engineer Émile Gagnan?

Jacques Cousteau was a naval lieutenant when he and Gagnan built it in France in the winter of 1942–43. Its twin-hose demand regulator became the foundation of all later scuba regulators.

Because dolphins must surface to breathe, how do they manage to sleep without drowning?

Half the brain at a time is the trick: one hemisphere sinks into deep sleep while the other stays alert, with the opposite eye left open. Fur seals in water do the same.

Which feature of the mammal face gradually moved to the top of the head to become a whale's blowhole?

Nostrils are what a blowhole is: a nose that migrated. A sperm whale blows only through its left one, while the right is sealed off inside the head.

Which cell structures, carrying their own DNA inherited only from the mother, perform aerobic respiration?

Mitochondria use oxygen to make ATP, with a yield more than ten times what fermentation manages. Their 'powerhouse of the cell' nickname was popularised by a 1957 Scientific American article.

Which radioactive gas, seeping from soil into basements, is the top cause of lung cancer in non-smokers?

Radon is denser than air, so it pools in basements and crawlspaces. In the United States it ranks second only to cigarette smoking as a cause of lung cancer.

Which lung infection is named after the 1976 veterans' convention in Philadelphia where it was first identified?

Legionnaires' disease killed more than two dozen people linked to that American Legion gathering. Its bacteria thrive in warm water, such as the cooling towers of large air conditioners.

Which disease caused the 1918 pandemic wrongly pinned on Spain because its newspapers were uncensored?

Influenza of the H1N1 subtype was behind it, and the outbreak did not begin in Spain. Wartime censors elsewhere suppressed the bad news, while the neutral Spanish press reported freely.

Smelling salts revive a fainting person by releasing which pungent gas that triggers a reflex to inhale?

Ammonia irritates the lining of the nose and lungs, setting off an inhalation reflex that makes the breathing muscles work faster. The salts were once sold as sal volatile or spirit of hartshorn.

Through which tiny pores, each flanked by a pair of guard cells, do plant leaves exchange gases with the air?

Stomata take their name from the Greek for 'mouth'. Water vapour escapes through the same openings, so a plant has to balance its gas exchange against drying out.

Which domestic animals are obligate nasal breathers, physically unable to draw air in through the mouth?

Horses have a soft palate that seals the mouth off from the lower airways, so every breath travels through the nose. Rabbits and rodents are built the same way.

Which temporary organ supplies an unborn baby with oxygen from the mother's blood until the first breath?

The placenta passes oxygen and nutrients from the mother's blood to the fetus and sends waste back the other way. It is joined to the baby by an umbilical cord about half a metre long.

Which cough-drop ingredient makes a blocked nose feel clearer by triggering cold receptors without opening it?

Menthol sets off the cold-sensitive TRPM8 receptors, so each breath feels like a rush of cool air. Tests find the sensation of decongestion without any measurable decongestant action.

Which chemical, released from mast cells when pollen meets the immune system, triggers hay fever's sneezing?

Histamine also makes small blood vessels leaky, which is why the nose runs and the eyes water. Mast cells cluster in the nose and mouth, where trouble is most likely to arrive.

Which nickname was given to an airway disease after factory workers fell ill inhaling artificial butter flavouring?

Popcorn lung came to public attention when eight former workers at a Missouri popcorn plant fell ill. The chemical blamed was diacetyl, which gives microwave popcorn its buttery taste.

Oxygen peaked at about 35% of the air some 280 million years ago, but roughly what share is it today?

About 21% is the modern figure, or 20.95% of dry air to be exact. The 35% peak spanned the late Carboniferous and Permian periods, and the level has swung up and down ever since.

Which acid do muscles produce during a hard sprint, when they break down glucose faster than oxygen can keep up?

Lactic acid takes its name from the Latin for milk, because it was first isolated from sour milk in 1780. Well-oxygenated muscle cells later burn it again as fuel.

Which breathing pattern, often set off by anxiety or panic, causes dizziness and tingling in the lips and hands?

Hyperventilation blows off waste gas faster than the body makes it, so the blood turns too alkaline. That shift, called respiratory alkalosis, is what brings on the tingling and faintness.

Which arteries, leaving the right ventricle, are the only ones in the adult body that carry oxygen-poor blood?

Pulmonary arteries flip the usual rule: they take spent blood to the lungs, and the veins of the same name bring the freshly oxygenated blood back.

Which narrow airways, about a millimetre wide or less, have no cartilage in their walls to hold them open?

The bronchioles are ringed with smooth muscle instead, which tightens or relaxes to change how much air flows through. The finest are half a millimetre across or less.

Which muscles lift the ribs up and outward during a breath in, widening the chest from side to side?

The intercostals work in layers: the external ones raise the ribs for a breath in, while the internal ones pull the ribs down and inward for a forced breath out.

The right half of the main breathing muscle sits higher than the left because which large organ rests beneath it?

The liver, the heaviest internal organ in the human body, rests under the right side of that muscle and holds it higher than the left.

By which passive process, driven only by a concentration gradient, does oxygen cross from the alveoli into the blood?

Diffusion costs the body no energy: oxygen simply moves from where it is concentrated to where it is scarce. The thinner the exchange surface, the faster the gas gets across.

Which passage behind the nose and mouth is the one stretch shared by both breathed air and swallowed food?

The pharynx comes in three sections, the nasopharynx, oropharynx and laryngopharynx. Below the last of them, the routes for air and food finally part.

Which chambers act as the bellows for a bird's rigid lungs and even reach inside its hollow bones?

Air sacs push air through a bird's lungs in one direction only, on the breath in and the breath out alike, so fresh air is always passing over the exchange surface.

Through which openings along an insect's body, which close to save water, does air enter the breathing tubes?

Spiracles lead into tubes that carry air straight to the tissues, so an insect's blood plays only a minor part in moving oxygen around.

Members of the largest family of which amphibians have no lungs and breathe through their skin and mouth lining?

Salamanders of the family Plethodontidae, more than 500 species strong, rely almost entirely on gas exchange through the skin and the tissues lining the mouth.

Some diving turtles take up oxygen underwater through a pair of pouches that open off which body part?

The cloaca is the single rear opening a turtle also uses for waste and reproduction. Sea cucumbers breathe in a similar way, drawing water in through the anus.

Which French chemist, guillotined in 1794, gave oxygen its name and recognised it as an element?

Antoine Lavoisier went to the guillotine on charges of tax fraud, despite appeals to spare him for his contributions to science. The French government exonerated him a year and a half later.

Which English theologian and chemist, who also invented soda water, isolated oxygen in 1774 by heating mercuric oxide?

Joseph Priestley called his new gas 'dephlogisticated air'. In his own lifetime much of his fame rested on carbonated water, which he devised in 1767.

Which childhood airway infection is known for a barking cough often likened to the call of a sea lion?

Croup swells the lining of the trachea, which also produces a harsh noise on breathing in and a hoarse voice. The symptoms usually get worse at night.

Which smoking-related lung condition breaks down the walls of the alveoli, leaving fewer, larger air spaces?

Emphysema shrinks the surface available for gas exchange, so less oxygen reaches the blood. It takes years to develop, which is why it mostly shows up in middle age or later.

Which skin sign, seen in the lips and fingertips, appears when blood oxygen saturation drops to about 85% or below?

Cyanosis is a bluish-purple tinge, caused by a build-up of hemoglobin that has given up its oxygen. Blue food dyes and large birthmarks can be mistaken for it.

Which hormone, released by the kidneys when oxygen runs low, was notoriously abused by professional cyclists?

Erythropoietin, or EPO, tells the bone marrow to turn out more oxygen-carrying cells. Riders confessed to using it in cycling's Festina affair, after a team car full of doping products was found.

Which gas law, published in 1662, explains why air flows into the lungs when the chest expands?

Boyle's law says the pressure of a gas rises as its volume shrinks and falls as it grows. In France the same rule is credited to the physicist Edme Mariotte.

Which cells, scattered through the lining of both the airways and the intestines, secrete the mucins that form mucus?

Goblet cells get their name from their shape: the top is swollen like a cup with mucus-laden granules, while the narrow base forms the stem.

Which swelling of the fingertips, known as a sign of disease since Hippocrates, often points to lung trouble?

Clubbing leaves the nails curved like the glass of a watch, which is why the sign also goes by the names watch-glass nails and drumstick fingers.

Which effect, named after the father of a famous Danish physicist, makes hemoglobin give up oxygen in acidic tissue?

The Bohr effect means hard-working, more acidic tissue pulls extra oxygen off passing hemoglobin. Christian Bohr described it in 1904; his son Niels became a Nobel laureate in physics.

Which deep, gasping pattern of respiration, first noted in advanced diabetes, signals severe metabolic acidosis?

Kussmaul breathing is the body's attempt to correct acid blood by breathing off more waste gas. Adolf Kussmaul, a 19th-century German physician, first noted it in patients with advanced diabetes.

Which medical term means coughing up blood that has come from the lungs or airways?

Hemoptysis means the blood comes from the bronchi, larynx, trachea or lungs. That separates it from hematemesis, which is the vomiting of blood.

Which capital's 1952 polio epidemic, with students ventilating patients by hand, led to the first intensive care unit?

Copenhagen's Bjørn Ibsen enlisted 200 medical students to pump air and oxygen into paralysed patients' lungs by hand. In 1953 he set up a dedicated ward for such care.

Which Spanish theologian, burned at the stake in Geneva, first described in Europe how blood passes through the lungs?

Michael Servetus tucked his account of the blood's route through the lungs into a religious treatise of 1553. John Calvin denounced him, and Geneva's council had him burned for heresy.

Which small clusters of chemoreceptor cells in the neck mainly detect a fall in the oxygen level of arterial blood?

The carotid bodies sit where each common carotid artery forks, sampling the blood that flows through them. Their firing climbs steeply once oxygen pressure drops below about 60 mmHg.

Which measure of how easily the lungs stretch, likened to a thick balloon when low, falls when lung tissue scars?

Compliance is the change in lung volume for a given change in pressure. A stiff, scarred lung behaves like a thick balloon, while an over-pliable one is likened to a grocery bag.

Which reflex, first reported in 1868, protects the lungs from over-inflating by cutting short a very deep breath in?

The Hering–Breuer reflex runs through the vagus nerve, as Josef Breuer showed while working for Ewald Hering in Vienna. Breuer later became a mentor to the young Sigmund Freud.

Obesity hypoventilation syndrome was first nicknamed after a sleepy, overweight boy in which Charles Dickens novel?

The Pickwick Papers features Joe, a markedly obese boy who keeps falling asleep during the day. Doctors in the 1950s borrowed him for the name 'Pickwickian syndrome'.

Which central compartment of the chest holds every organ of the thorax except the lungs themselves?

The mediastinum takes its name from a Latin word for 'midway'. It houses the esophagus, the trachea, the thymus and the great vessels, all packed in loose connective tissue.

Which tiny vessels wrap each alveolus in a fine mesh that covers about 70% of its surface?

Capillaries form the blood side of the lung's gas-exchange surface: oxygen passes across the thin alveolar membrane into them, and waste gas passes out the other way.

Which fleshy projection hanging from the soft palate helps make the throaty 'r' sound of French?

The uvula shapes uvular consonants by narrowing the airflow against the back of the tongue. It also produces plenty of thin saliva, which is thought to keep the throat lubricated.