science

Inhalation

Inhalation is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Inhalation rather than just read about it. In short: Inhalation (or inspiration) happens when air or other gases enter the lungs. Inhalation of air Inhalation of air, as part of the cycle of breathing, is a vital process for all human life.

Key takeaways

Inhalation belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Inhalation to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Inhalation from memory before moving on to harder problems.

Reference excerpt

Inhalation (or inspiration) happens when air or other gases enter the lungs.

Inhalation of air Inhalation of air, as part of the cycle of breathing, is a vital process for all human life. The process is autonomic (though there are exceptions in some disease states) and does not need conscious control or effort. However, breathing can be consciously controlled or interrupted (within limits). Breathing allows oxygen (which humans and a lot of other species need for survival) to enter the lungs, from where it can be absorbed into the bloodstream.

Other substances – accidental Examples of accidental inhalation includes inhalation of water (e.g. in drowning), smoke, food, vomitus and less common foreign substances (e.g. tooth fragments, coins, batteries, small toy parts, needles).

Other substances – deliberate

Recreational use Nitrous oxide ("laughing gas") has been used recreationally since 1899 for its ability to induce euphoria, hallucinogenic states and relaxation, and is legal in some countries. Helium can be inhaled to give the voice a reedy, duck-like quality, but this can be dangerous as the gas is an asphyxiant and displaces the oxygen needed for normal respiration. Various illegal gaseous, vapourised or aerosolized recreational drugs exist, and are classed as inhalants.

Medical use

Diagnostic Various specialized investigations use the inhalation of known substances for diagnostic purposes. Examples include pulmonary function testing (e.g. nitrogen washout test, diffusion capacity testing (carbon monoxide, helium, methane)) and diagnostic radiology (e.g. radioactive xenon isotopes).

Therapeutic Gases and other drugs used in anaesthesia include oxygen, nitrous oxide, helium, xenon, volatile anaesthetic agents. Medication for asthma, croup, cystic fibrosis and some other conditions.

Mechanism Inhalation begins with the contraction of the muscles attached to the rib cage; this causes an expansion in the chest cavity. Then takes place the onset of contraction of the thoracic diaphragm, which results in expansion of the intrapleural space and an increase in negative pressure according to Boyle's law. This negative pressure generates airflow because of the pressure difference between the atmosphere and alveolus. The inflow of air into the lungs occurs via the respiratory airways. In health, these airways begin with the nose. It is possible to begin with the mouth, which is the backup breathing system. However, chronic mouth breathing leads to, or is a sign of, illness, and there is no mucus in the mouth to trap unwanted substances unlike the nostrils. They end in the microscopic dead-end sacs (alveoli) always opened, though the diameters of the various airways can be changed by the sympathetic and parasympathetic nervous systems. The alveolar air pressure is therefore always close to atmospheric air pressure (about 100 kPa at sea level) at rest, with the pressure gradients that cause air to move in and out of the lungs during breathing rarely exceeding 2–3 kPa. Other muscles that can be involved in inhalation include:

External intercostal muscles Scalene muscles Sternocleidomastoid muscle Trapezius muscle

Hyperinflation

Hyperinflation or hyperaeration is where the lung volume is abnormally increased, with increased filling of the alveoli. This results in an increased radiolucency on X-ray, a reduction in lung markings and depression of the diaphragm. It may occur in partial obstruction of a large airway, as in e.g. congenital lobar emphysema, bronchial atresia and mucus plugs in asthma.

Yoga Yogis such as B. K. S. Iyengar advocate both inhaling and exhaling through the nose in the practice of yoga, rather than inhaling through the nose and exhaling through the mouth. They tell their students that the "nose is for breathing, the mouth is for eating."

Illustrations

Worked examples

Example 1 — a first encounter with Inhalation

Start with the simplest possible case. Write down what Inhalation claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Inhalation before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Inhalation ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Inhalation

In research: Inhalation appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Inhalation in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Inhalation is common in secondary-school and first-year university syllabi. It links to neighbouring topics Respiration, Respiratory physiology, so understanding it makes those chapters shorter.
In everyday life: Look for Inhalation outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Inhalation in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Inhalation means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Inhalation out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Inhalation in simple terms?

Inhalation (or inspiration) happens when air or other gases enter the lungs. Inhalation of air Inhalation of air, as part of the cycle of breathing, is a vital process for all human life.

Why does Inhalation matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Inhalation?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Inhalation.