50 Fun Facts About Respiratory System

How many lobes does the right human lung have?

The left lung has only two lobes, because it gives up room to the heart and has a cardiac notch instead of a middle lobe.

Which muscle is described as the most important muscle of respiration?

When it contracts the chest cavity gets bigger, pressure drops, and air is pulled in; relaxing it pushes the air back out.

What is the common name for the trachea?

It links the larynx to the bronchi and is found in almost every land vertebrate with lungs.

Roughly how many rings of hyaline cartilage surround the adult trachea?

The rings are incomplete and C-shaped, with the open side at the back so the oesophagus behind it can bulge when you swallow.

What shape are the cartilage hoops of the trachea?

Complete O rings do occur as a rare abnormality and can narrow the airway enough to cause breathing trouble.

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

The split sits at about the level of the fourth thoracic vertebra, though it shifts a little as you breathe.

Which main bronchus is wider, shorter and more vertical?

That geometry is why inhaled food or small objects tend to end up in the right lung.

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

The left bronchus leaves the windpipe at a sharper angle, so gravity and airflow favour the right side.

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

Together they give a gas-exchange surface of roughly 70 to 80 square metres, packed into a chest.

The word 'alveolus' comes from Latin meaning what?

The same root gives dentists their 'alveolar' bone, the sockets that hold teeth.

Which alveolar cells release pulmonary surfactant?

They are small and cube-shaped, and can also multiply to replace damaged type I cells after injury.

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

With less surface tension the lung inflates far more easily, which cuts the work of every breath.

Insufficient surfactant in preterm babies causes which condition?

Adequate surfactant is not made until around 35 weeks of gestation, which is why very early babies struggle to breathe.

What is the larynx commonly called?

It sits at the top of the neck and does three jobs: breathing, making sound and keeping food out of the windpipe.

How many cartilages make up the skeleton of the human larynx?

Three are single (epiglottic, thyroid, cricoid) and three come in pairs (arytenoid, corniculate, cuneiform).

Which laryngeal cartilage forms the Adam's apple?

Anatomists call the bump the laryngeal prominence; it is the only laryngeal cartilage found exclusively in mammals.

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

When you swallow, the tongue levers it down over the glottis so the mouthful slides into the oesophagus instead.

Into how many sections is the human pharynx conventionally divided?

They are the nasopharynx behind the nose, the oropharynx behind the mouth and the laryngopharynx that leads on to the oesophagus.

The adenoids, found in the nasopharynx, are also known as what?

They are lumps of lymphoid tissue on the back wall of the nasopharynx and form part of Waldeyer's tonsillar ring.

Which passage links the middle ear to the nasopharynx?

That link is why your ears pop when you swallow or yawn on a plane: it lets the middle ear equalise pressure.

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

Medical students remember the roots with the rhyme 'C3, 4, 5 keeps you alive'.

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

Moving down enlarges the thoracic cavity and drops the pressure inside it, so air flows into the lungs.

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

The stomach or lower oesophagus slips up into the thorax, which is why the condition is linked to acid reflux.

What is a hiccup, physiologically?

The glottis snaps shut about 35 milliseconds after the spasm, and that closure makes the 'hic'.

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

They began in 1922 and stopped in 1990, an estimated 430 million hiccups in all.

What is the scientific name for a hiccup?

It comes from the Latin for 'sob'; sternutation is a sneeze and tussis is a cough.

What is the formal term for a sneeze?

A sneeze blasts air out through the nose and mouth, usually because something is irritating the lining of the nose.

Sneezing triggered by sudden bright light is called what?

It is sometimes nicknamed ACHOO syndrome, and it runs in families.

What is the potential space between the two pleurae around each lung called?

It holds a thin film of serous fluid that lets the lung slide against the chest wall with each breath.

Which pleura covers the surface of the lung itself?

The parietal pleura is the outer layer lining the chest wall; only a film of fluid separates the two.

What is the resting tidal volume of an adult human, roughly?

Of that half-litre, around 150 ml only refills the airways' dead space and never reaches the alveoli.

How much air sits in the adult airways' dead space after exhaling?

That stale air is breathed back into the alveoli before any fresh air arrives, so only about 350 ml of each breath is new.

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

They respond chiefly to carbon dioxide in the blood, which is why holding your breath soon becomes unbearable even with plenty of oxygen left.

At sea level, breathing rate is controlled mainly by the blood level of which gas?

Oxygen is allowed to drift across a fairly wide range before the body reacts; CO2 is watched far more tightly.

What percentage of inhaled air, by volume, is nitrogen?

Oxygen is just under 21%, and the rest is a pinch of argon, carbon dioxide and other trace gases.

How many oxygen molecules can one mammalian hemoglobin molecule carry?

Each of its four subunits holds an iron-containing heme group, and each heme binds one oxygen.

Who determined the molecular structure of hemoglobin in 1959?

The work earned him a share of the 1962 Nobel Prize in Chemistry with John Kendrew, who solved myoglobin.

The word 'asthma' comes from a Greek word meaning what?

Hippocrates named it as a distinct respiratory problem around 450 BC.

Which inhaled drug is commonly used to treat a sudden asthma attack?

Americans know it as albuterol; it relaxes the airway muscles within minutes, while steroids handle the underlying inflammation.

Which bacterium is isolated in nearly half of community-acquired pneumonia cases?

Infection with it classically produces rusty-coloured sputum, and a vaccine against it exists.

Which physician called pneumonia the 'captain of the men of death' in 1918?

By then it had overtaken tuberculosis as one of the leading killers; Osler is often called the father of modern medicine.

Who identified the bacillus that causes tuberculosis on 24 March 1882?

World Tuberculosis Day is still held every 24 March to mark the announcement.

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

In that century it was blamed for about a quarter of all deaths in Europe.

What do the letters BCG stand for in the name of the TB vaccine?

Albert Calmette and Camille Guérin were the French scientists who developed it from a weakened bovine strain.

Roughly what fraction of the world's population is estimated to have latent TB?

That is around 2 billion people carrying the bacterium without active disease.

In spirometry, what does FEV1 measure?

It falls in obstructive diseases like asthma and COPD, because narrowed airways slow the outward rush of air.

Roughly how many motile cilia does each respiratory epithelial cell carry?

They beat in waves to sweep mucus and trapped debris up and away from the lungs, a process called mucociliary clearance.

What is the zoologists' academic name for gills?

It comes from the Greek for 'gills', and it survives in words like 'branchial arches'.

Snakes typically rely on which lung as their major respiratory organ?

The left lung is greatly reduced or missing altogether, which suits a body that is essentially one long tube.

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

Estimates run 50 to 75 square metres, which is actually less than half a singles court, so the textbook comparison is generous.