View source for Biology:Inhalation

{{short description|Flow of the respiratory current into an organism}}
[[File:Inhalation diagram.svg|thumb|Diagram showing inhalation]]
'''Inhalation''' (or '''inspiration''') is the process of drawing air or other gases into the [[Medicine:Respiratory tract|respiratory tract]], primarily for the purpose of [[Physics:Breathing|breathing]] and oxygen exchange within the body. It is a fundamental physiological function in humans and many other organisms, essential for sustaining life. Inhalation is the first phase of respiration, allowing the exchange of [[Chemistry:Oxygen|oxygen]] and [[Chemistry:Carbon dioxide|carbon dioxide]] between the body and the environment, vital for the body's metabolic processes. This article delves into the mechanics of inhalation, its significance in various contexts, and its potential impact on health.
==Physiology==
The process of inhalation involves a series of coordinated movements and physiological mechanisms. The primary anatomical structures involved in inhalation are the respiratory system, which includes the [[Medicine:Nose|nose]], [[Biology:Mouth|mouth]], [[Biology:Pharynx|pharynx]], [[Medicine:Larynx|larynx]], [[Biology:Trachea|trachea]], bronchi, and lungs. Here is a brief overview of the inhalation process:
#Inspiration: Inhalation begins with the contraction of the thoracic diaphragm, a dome-shaped muscle that separates the chest cavity from the abdominal cavity. The diaphragm contracts and moves downward, increasing the volume of the thoracic cavity.
#Air entry: When a person or animal inhales, the diaphragm, located below the lungs, contracts, and the intercostal muscles between the ribs expand the chest cavity. This expansion creates a lower pressure inside the chest compared to the atmosphere, causing air to flow into the lungs.
#Air filtration: The nasal passages and the mouth act as entry points for air. These passages are lined with tiny hair-like structures called cilia and mucus-producing cells that help filter and humidify the incoming air, removing particles and debris before it reaches the lungs.
#[[Physics:Gas exchange|Gas exchange]]: Once the air enters the lungs, it travels through a branching network of tubes known as the bronchial tree, ultimately reaching tiny air sacs called alveoli. In the alveoli, oxygen from the inhaled air diffuses into the bloodstream, while carbon dioxide, a waste product of metabolism, is released from the blood into the alveoli for exhalation.
#Expiration: [[Biology:Exhalation|Exhalation]] is a passive process, primarily driven by the relaxation of the diaphragm and the elastic recoil of the lungs. This expels carbon dioxide from the body.<ref>Guyton, A. C., & Hall, J. E. (2006). Textbook of Medical Physiology. Elsevier Saunders.</ref><ref>West, J. B. (2000). Respiratory Physiology: The Essentials. Lippincott Williams & Wilkins</ref>
== Other substances – accidental ==
Examples of accidental inhalation includes inhalation of water (e.g. in drowning), smoke, food, vomitus and less common foreign substances<ref>{{Cite journal|last2=Lauriello|first2=M|last3=Bellussi|first3=L|last4=Passali|first4=GC|last5=Passali|first5=FM|last6=Gregori|first6=D|date=2010|title=Foreign body inhalation in children: an update|pmc=2881610|journal=Acta Otorhinolaryngol Ital|pmid=20559470|last1=Passàli|first1=D|volume=30|issue=1|pages=27–32}}</ref> (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, called inhalants

=== Medical use ===

==== Diagnostic ====

Various specialized investigations use the inhalation of known substances for diagnostic purposes. Examples include [[Medicine:Pulmonary function testing|pulmonary function testing]] (e.g. [[Medicine:Nitrogen washout|nitrogen washout]] test, [[Medicine:Diffusing capacity|diffusion capacity]] testing ([[Chemistry:Carbon monoxide|carbon monoxide]], [[Chemistry:Helium|helium]], [[Chemistry:Methane|methane]])) and diagnostic radiology (e.g. [[Physics:Isotopes of xenon|radioactive xenon isotopes]]).

==== Therapeutic ====

Gases and other drugs used in anaesthesia include oxygen, nitrous oxide, helium, xenon, [[Chemistry:Inhalational anaesthetic|volatile anaesthetic agents]]. Medication for [[Medicine:Asthma|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 [[Biology:Obligate nasal breathing|begin with the nose]].<ref name=cc>{{cite web
|url=https://health.clevelandclinic.org/breathe-mouth-nose/
|title=Should You Breathe Through Your Mouth or Your Nose?
|access-date=2020-06-28
|last=Turowski
|first=Jason
|date=2016-04-29
|publisher=Cleveland Clinic
}}</ref><ref name="guardian">{{cite web|title=Your Nose, the Guardian of Your Lungs|url=https://www.bmc.org/otolaryngology-head-neck-surgery/resources/your-nose-guardian-your-lungs|access-date=2020-06-29|publisher=Boston Medical Center}}</ref> It is possible to begin with the mouth, which is the backup breathing system. However, chronic [[Medicine:Mouth breathing|mouth breathing]] leads to, or is a sign of, illness.<ref name=harmful>{{cite web
|url=https://www.nbcnews.com/healthmain/mouth-breathing-gross-harmful-your-health-1C6437430
|title='Mouth-breathing' gross, harmful to your health
|access-date=2020-06-28
|last=Dahl
|first=Melissa
|date=2011-01-11
|publisher=NBC News
}}</ref><ref name="role">{{cite web
|url=https://www.journal-imab-bg.org/issues-2018/issue1/JofIMAB-2018-24-1p1878-1882.pdf
|title=THE ROLE OF MOUTH BREATHING ON DENTITION DEVELOPMENT AND FORMATION
|access-date=2020-05-31
|last=Valcheva
|first=Zornitsa
|date=January 2018
|publisher=Journal of IMAB
}}</ref><ref name="nesnpr">{{cite web
|url=https://www.npr.org/transcripts/862963172
|title=How The 'Lost Art' Of Breathing Can Impact Sleep And Resilience
|access-date=2020-06-23
|last=Gross
|first=Terry
|date=2020-05-27
|publisher=National Public Radio (NPR)/Fresh Air
}}</ref> They end in the microscopic dead-end sacs(alveoli) 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&nbsp;[[Pascal (unit)|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&nbsp;kPa.<ref name="Chrisvan L 1995">{{cite journal |last1=Koen |first1=Chrisvan L. |last2=Koeslag |first2=Johan H. | title=On the stability of subatmospheric intrapleural and intracranial pressures |journal= News in Physiological Sciences | date=1995 |volume=10 |issue=4 |pages=176–178 |doi=10.1152/physiologyonline.1995.10.4.176}}</ref><ref name="Williams & Wilkins">{{cite book |last1=West |first1=J.B. |title=Respiratory physiology: the essentials. |location=Baltimore |publisher=Williams & Wilkins |date=1985| pages= 21–30, 84–84, 98–101 }}</ref>

Other muscles that can be involved in inhalation include:<ref>{{cite book| title= Essentials of Human Physiology| first= Thomas M. |last= Nosek| chapter=Section 4/4ch2/s4ch2_10 |chapter-url=http://humanphysiology.tuars.com/program/section4/4ch2/s4ch2_10.htm |archive-url=https://web.archive.org/web/20160324124828/http://humanphysiology.tuars.com/program/section4/4ch2/s4ch2_10.htm|archive-date=2016-03-24}}{{dead link|date=December 2010}}</ref>
* External intercostal muscles
* [[Medicine:Scalene muscles|Scalene muscles]]
* [[Medicine:Sternocleidomastoid muscle|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 [[Physics:Radiodensity|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 [[Biology:Atresia|atresia]] and mucus plugs in [[Medicine:Asthma|asthma]].<ref>{{cite web|url=http://www.medcyclopaedia.com/library/topics/volume_vii/h/hyperinflation.aspx|archive-url=https://archive.today/20111208222639/http://www.medcyclopaedia.com/library/topics/volume_vii/h/hyperinflation.aspx|url-status=dead|archive-date=2011-12-08|title=Hyperinflation|publisher=[[Company:General Electric|GE]]|work=Medcyclopaedia}}</ref>

==Yoga==
Yogis such as B. K. S. Iyengar advocate both [[Biology:Obligate nasal breathing|inhaling and exhaling through the nose]] in the practice of [[Philosophy:Yoga|yoga]], rather than inhaling through the nose and [[Medicine:Mouth breathing|exhaling through the mouth]].<ref name=yj>{{cite web
|url=https://www.yogajournal.com/practice/take-a-breath
|title=Q&A: Is Mouth Breathing OK in Yoga?
|access-date=2020-06-26
|last=Yoga Journal Editors
|date=2017-04-12
|publisher=Yoga Journal
}}</ref><ref name=dummies>{{cite web
|url=https://www.dummies.com/health/exercise/yoga/yogic-breathing-tips-for-breathing-through-your-nose-most-of-the-time/
|title=Yogic Breathing: Tips for Breathing through Your Nose (Most of the Time)
|access-date=2020-06-26
|last=Payne
|first=Larry
|publisher=Yoga For Dummies, 3rd Edition
}}</ref><ref name=guide>{{cite web
|url=https://www.himalayaninstitute.org/wisdom-library/yogic-breathing-study-guide/
|title=Yogic Breathing: A Study Guide
|access-date=2020-06-26
|last=Himalayan Institute Core Faculty
|first=Himalayan Institute Core Faculty
|date=2017-07-13
|publisher=Himalayan Institute of Yoga Science and Philosophy
}}</ref> They tell their students that the "nose is for breathing, the mouth is for eating."<ref name=dummies/><ref name=sparks>{{cite book
|url=https://books.google.com/books?id=QPk_nshsngoC&q=%22the+nose+is+for+breathing%2C+the+mouth+is+for+eating%22+yoga&pg=RA1-PA11
|title=Yoga Sparks
|access-date=2020-05-31
|last=Krucoff
|first=Carol
|date=2013
|publisher=New Harbinger Publications
|isbn=9781608827022
}}</ref><ref name=run>{{cite book
|url=https://books.google.com/books?id=fEm6XnTajm0C&q=%22the+nose+is+for+breathing%2C+the+mouth+is+for+eating%22+yoga&pg=PA108
|title=Eat and Run
|access-date=2020-05-31
|last=Jurek
|first=Scott
|date=2012
|publisher=Houghton Mifflin
|isbn=978-0547569659
}}</ref><ref name=yj/>

==See also==
* [[Biology:Exhalation|Exhalation]]
* [[Medicine:Inhalant|Inhalant]] – psychoactive drugs consumed through inhalation
* List of terms of lung size and activity
* [[Medicine:Mouth breathing|Mouth breathing]]
* [[Biology:Obligate nasal breathing|Obligate nasal breathing]]
* Respiratory system
* [[Medicine:Smoking|Smoking]] - a specific inhalation route
* [[Physics:Breathing|Breathing]]
* [[Biology:Work of breathing|Work of breathing]]

==Further reading==
* {{Cite book|title=Breath: The New Science of a Lost Art
|last=Nestor|first=James|publisher=Riverhead Books |year=2020|isbn= 978-0735213616 }}

==References==
{{reflist}}

{{Dosage forms}}
{{Respiratory physiology}}

[[Category:Respiration]]
[[Category:Respiratory physiology]]

{{Sourceattribution|Inhalation}}