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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 Control may refer to: Basic meanings Economics and business * Control (management), an element of management * Control, an element of management accounting * Comptroller (or controller), a senior financial officer in an organization * Controlli ...
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

Legal – helium, nitrous oxide (" laughing gas") Illegal – various gaseous, vaporised or aerosolized recreational drugs


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 Carbon monoxide ( chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simpl ...
,
helium Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic ta ...
,
methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of 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 Asthma is a long-term inflammatory disease of the airways of the lungs. It is characterized by variable and recurring symptoms, reversible airflow obstruction, and easily triggered bronchospasms. Symptoms include episodes of wheezing, co ...
, 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 The respiratory tract is the subdivision of the respiratory system involved with the process of respiration in mammals. The respiratory tract is lined with respiratory epithelium as respiratory mucosa. Air is breathed in through the nose to th ...
. 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. They end in the microscopic dead-end sacs(
alveoli Alveolus (; pl. alveoli, adj. alveolar) is a general anatomical term for a concave cavity or pit. Uses in anatomy and zoology * Pulmonary alveolus, an air sac in the lungs ** Alveolar cell or pneumocyte ** Alveolar duct ** Alveolar macrophage * M ...
) always opened, though the diameters of the various sections 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 The external intercostal muscles, or external intercostals (Intercostales externi) are eleven in number on both sides. Structure The muscles extend from the tubercles of the ribs behind, to the cartilages of the ribs in front, where they en ...
* 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 Atresia is a condition in which an orifice or passage in the body is (usually abnormally) closed or absent. Examples of atresia include: *Aural atresia, a congenital deformity where the ear canal is underdeveloped. * Biliary atresia, a condition i ...
and mucus plugs in
asthma Asthma is a long-term inflammatory disease of the airways of the lungs. It is characterized by variable and recurring symptoms, reversible airflow obstruction, and easily triggered bronchospasms. Symptoms include episodes of wheezing, co ...
.


Yoga

Yogis such as
B. K. S. Iyengar Bellur Krishnamachar Sundararaja Iyengar (14 December 1918 – 20 August 2014) was an Indian teacher of yoga and author. He is founder of the style of yoga as exercise, known as " Iyengar Yoga", and was considered one of the foremost yoga guru ...
advocate both inhaling and exhaling through the nose in the practice of
yoga Yoga (; sa, योग, lit=yoke' or 'union ) is a group of physical, mental, and spiritual practices or disciplines which originated in ancient India and aim to control (yoke) and still the mind, recognizing a detached witness-consciou ...
, 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."


See also

* Exhalation * Inhalant – psychoactive drugs consumed through inhalation *
List of terms of lung size and activity Following are terms that specify a type of lung size and/or activity. More specific definitions may be found in individual articles. *Eupnea – normal breathing *Apnea – absence of breathing *Bradypnea – decreased breathing rate *Dyspnea or '' ...
* Mouth breathing * Obligate nasal breathing *
Respiratory system The respiratory system (also respiratory apparatus, ventilatory system) is a biological system consisting of specific organs and structures used for gas exchange in animals and plants. The anatomy and physiology that make this happen varies g ...
*
Smoking Smoking is a practice in which a substance is burned and the resulting smoke is typically breathed in to be tasted and absorbed into the bloodstream. Most commonly, the substance used is the dried leaves of the tobacco plant, which have b ...
- a specific inhalation route * Breathing *
Work of breathing Work of breathing (WOB) is the energy expended to inhale and exhale a breathing gas. It is usually expressed as work per unit volume, for example, joules/litre, or as a work rate (power), such as joules/min or equivalent units, as it is not particu ...


Further reading

*


References

{{Respiratory physiology Respiration Respiratory physiology