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Breathing (or ventilation) is the process of moving
air File:Atmosphere gas proportions.svg, Composition of Earth's atmosphere by volume, excluding water vapor. Lower pie represents trace gases that together compose about 0.043391% of the atmosphere (0.04402961% at April 2019 concentration ). Number ...

air
out and in the
lung The lungs are the primary organs An organ is a group of tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A given organ's tissues can be broadly categorized as parenchyma ...

lung
s to facilitate
gas exchange Gas exchange is the physical process by which gases move passively by Diffusion#Diffusion vs. bulk flow, diffusion across a surface. For example, this surface might be the air/water interface of a water body, the surface of a gas bubble in a liquid ...

gas exchange
with the internal environment, mostly to flush out
carbon dioxide Carbon dioxide (chemical formula A chemical formula is a way of presenting information about the chemical proportions of s that constitute a particular or molecule, using symbols, numbers, and sometimes also other symbols, such as pare ...

carbon dioxide
and bring in
oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

oxygen
. All aerobic creatures need oxygen for
cellular respiration upright=2.5, Typical eukaryotic cell Cellular respiration is a set of metabolic Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life Life is a characteristic that distinguishes physical entities ...

cellular respiration
, which uses the oxygen to break down foods for energy and produces carbon dioxide as a waste product. Breathing, or "external respiration", brings air into the lungs where gas exchange takes place in the
alveoli Alveolus (pl. alveoli, adj. alveolar) is a general anatomical term for a concave cavity or pit. Alveolus may refer to: In anatomy and zoology in general * Pulmonary alveolus, an air sac in the lungs ** Alveolar cell or pneumocyte ** Alveolar duct ...
through
diffusion Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration In chemistry Chemistry is the study of the properties and behavior of . It is a that covers ...

diffusion
. The body's
circulatory system The circulatory system, also called the cardiovascular system or the vascular system, is an organ system An organ system is a biological system A biological system is a complex network Network and networking may refer to: Arts, entertai ...
transports these gases to and from the cells, where "cellular respiration" takes place. The breathing of all
vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic ma ...
s with lungs consists of repetitive cycles of
inhalation Inhalation happens when air or other gases enter the lungs. Inhalation of air Inhalation of air, as part of the cycle of breathing File:X-ray video of a female American alligator (Alligator mississippiensis) while breathing - pone.0004497. ...

inhalation
and
exhalation Exhalation (or expiration) is the flow of the breath upright=1.4, X-ray video of a female American alligator while breathing. Breathing (or ventilation) is the process of moving air File:Atmosphere gas proportions.svg, Composition of ...
through a highly branched system of tubes or
airways
airways
which lead from the nose to the alveoli. The number of respiratory cycles per minute is the breathing or
respiratory rate The respiratory rate is the rate at which breathing File:X-ray video of a female American alligator (Alligator mississippiensis) while breathing - pone.0004497.s009.ogv, upright=1.4, X-ray video of a female American alligator while breathing. ...
, and is one of the four primary
vital signs Vital signs (also known as vitals) are a group of the four to six most important that indicate the status of the body’s (life-sustaining) functions. These measurements are taken to help assess the general physical health of a person, give clu ...
of life. Under normal conditions the breathing depth and rate is automatically, and unconsciously, controlled by several homeostatic mechanisms which keep the
partial pressure In a mixture of gases, each constituent gas has a partial pressure which is the notional pressure of that constituent gas if it alone occupied the entire volume of the original mixture at the same temperature. The total pressure of an ideal gas mix ...
s of
carbon dioxide Carbon dioxide (chemical formula A chemical formula is a way of presenting information about the chemical proportions of s that constitute a particular or molecule, using symbols, numbers, and sometimes also other symbols, such as pare ...

carbon dioxide
and
oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

oxygen
in the arterial blood constant. Keeping the partial pressure of carbon dioxide in the arterial blood unchanged under a wide variety of physiological circumstances, contributes significantly to tight control of the pH of the
extracellular fluids Extracellular fluid (ECF) denotes all body fluid Body fluids, bodily fluids, or biofluids are liquid A liquid is a nearly incompressible fluid In physics, a fluid is a substance that continually Deformation (mechanics), deforms (flows) un ...
(ECF). Over-breathing (
hyperventilation Hyperventilation occurs when the rate or tidal volume of breathing eliminates more carbon dioxide than the body can produce. This leads to hypocapnia, a reduced concentration of carbon dioxide dissolved in the blood. The body normally attempts ...
) and under-breathing (
hypoventilation Hypoventilation (also known as respiratory depression) occurs when ventilation is inadequate (''hypo'' meaning "below") to perform needed respiratory gas exchange. By definition it causes an increased concentration of carbon dioxide Carbon d ...
), which decrease and increase the arterial partial pressure of carbon dioxide respectively, cause a rise in the pH of ECF in the first case, and a lowering of the pH in the second. Both cause distressing symptoms. Breathing has other important functions. It provides a mechanism for
speech Speech is human vocal communication Communication (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''c ...

speech
,
laughter Laughter is a pleasant physical reaction consisting usually of rhythmical, often audible contractions of the diaphragm Diaphragm may refer to: * Diaphragm (anatomy) or thoracic diaphragm, a thin sheet of muscle between the thorax and the abdomen ...

laughter
and similar expressions of the emotions. It is also used for
reflex In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanism ...

reflex
es such as
yawning A yawn is a reflex In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, phys ...

yawning
,
coughing A cough is a sudden expulsion of air through the large breathing passages that can help clear them of fluids, irritants, foreign particles and Microorganism, microbes. As a protective reflex, coughing can be repetitive with the cough reflex follow ...
and
sneezing A sneeze, or sternutation, is a semi-autonomous, convulsive expulsion of air from the lungs through the nose and mouth, usually caused by foreign particles irritating the nasal mucous membrane, mucosa. A sneeze expels air forcibly from the mouth an ...
. Animals that cannot
thermoregulate Thermoregulation is the ability of an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the Life#Biology, properties of life. It is a sy ...
by
perspiration Perspiration, also known as sweating, is the production of fluids secreted by the sweat gland Sweat glands, also known as sudoriferous or sudoriparous glands, , are small tubular structures of the skin Skin is the layer of usually soft, fl ...
, because they lack sufficient
sweat gland Sweat glands, also known as sudoriferous or sudoriparous glands, , are small tubular structures of the skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate Vertebrates () comprise all species of an ...
s, may lose heat by evaporation through panting.


Mechanics

The lungs are not capable of inflating themselves, and will expand only when there is an increase in the volume of the thoracic cavity. In humans, as in the other
mammals Mammals (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the R ...
, this is achieved primarily through the contraction of the
diaphragm Diaphragm may refer to: * Diaphragm (anatomy) or thoracic diaphragm, a thin sheet of muscle between the thorax and the abdomen * Diaphragm (optics), a stop in the light path of a lens, having an aperture that regulates the amount of light that pass ...
, but also by the contraction of the
intercostal muscles Intercostal muscles are many different groups of muscle Skeletal muscles (commonly referred to as muscles) are organs An organ is a group of tissues with similar functions. Plant life and animal life rely on many organs that co-exist in ...
which pull the
rib cage The rib cage is the arrangement of ribs attached to the vertebral column and sternum in the thorax of most vertebrates that encloses and protects the vital organs such as the heart, lungs and great vessels. In humans, the rib cage and the sternum ...

rib cage
upwards and outwards as shown in the diagrams on the right. During forceful inhalation (Figure on the right) the accessory muscles of inhalation, which connect the ribs and
sternum The sternum or breastbone is a long flat bone located in the central part of the chest. It connects to the ribs via cartilage and forms the front of the rib cage, thus helping to protect the heart, human lung, lungs, and major blood vessels from in ...

sternum
to the
cervical vertebrae In tetrapod Tetrapods (; from Greek 'four' and 'foot') are four-limbed animals constituting the superclass Tetrapoda . It includes extant and extinct amphibians, reptiles (including dinosaurs and therefore birds), and synapsids (including ...

cervical vertebrae
and base of the skull, in many cases through an intermediary attachment to the
clavicles The clavicle, or collarbone, is a slender, S-shaped bone approximately 6 inches (15 cm) long bone The long bones are those that are longer than they are wide. They are one of five types of bone A bone is a Stiffness, rigid tissue (ana ...
, exaggerate the pump handle and bucket handle movements (see illustrations on the left), bringing about a greater change in the volume of the chest cavity. During exhalation (breathing out), at rest, all the muscles of inhalation relax, returning the chest and abdomen to a position called the “resting position”, which is determined by their anatomical elasticity. At this point the lungs contain the
functional residual capacity Functional residual capacity (FRC) is the volume of air present in the lungs at the end of passive expiration. At FRC, the opposing elastic recoil forces of the lungs and chest wall are in equilibrium and there is no exertion by the thoracic ...
of air, which, in the adult human, has a volume of about 2.5–3.0 liters. During heavy breathing (
hyperpnea Hyperpnea (forced respiration) is increased volume Volume is the quantity of three-dimensional space enclosed by a closed surface, for example, the space that a substance ( solid, liquid, gas, or plasma) or shape occupies or contains. Volume ...
) as, for instance, during exercise, exhalation is brought about by relaxation of all the muscles of inhalation, (in the same way as at rest), but, in addition, the abdominal muscles, instead of being passive, now contract strongly causing the rib cage to be pulled downwards (front and sides). This not only decreases the size of the rib cage but also pushes the abdominal organs upwards against the diaphragm which consequently bulges deeply into the thorax. The end-exhalatory lung volume is now less air than the resting "functional residual capacity". However, in a normal mammal, the lungs cannot be emptied completely. In an adult human, there is always still at least one liter of residual air left in the lungs after maximum exhalation.
Diaphragmatic breathing Diaphragmatic breathing, or deep breathing, is breathing that is done by contracting the diaphragm, a muscle located horizontally between the thoracic cavity and abdominal cavity The abdominal cavity is a large body cavity in humans and many o ...

Diaphragmatic breathing
causes the abdomen to rhythmically bulge out and fall back. It is, therefore, often referred to as "abdominal breathing". These terms are often used interchangeably because they describe the same action. When the accessory muscles of inhalation are activated, especially during labored breathing, the clavicles are pulled upwards, as explained above. This external manifestation of the use of the accessory muscles of inhalation is sometimes referred to as , seen especially during
asthma Asthma is a long-term Long-Term Capital Management L.P. (LTCM) was a hedge fund''A financial History of the United States Volume II: 1970–2001'', Jerry W. Markham, Chapter 5: "Bank Consolidation", M. E. Sharpe, Inc., 2002 based in Greenwich, ...

asthma
attacks and in people with
chronic obstructive pulmonary disease Chronic obstructive pulmonary disease (COPD) is a type of progressive lung disease The lungs are the primary Organ (anatomy), organs of the respiratory system in humans and many other animals including a few fish and some snails. In mammal ...
.


Passage of air


Upper airways

Ideally, air is breathed first out and secondly in through the nose. The
nasal cavities The nasal cavity is a large, air-filled space above and behind the nose A nose is a protuberance in vertebrates that houses the nostrils, or nares, which receive and expel air for Respiration (physiology), respiration alongside the mouth. Beh ...

nasal cavities
(between the
nostril A nostril (or naris , plural ''nares'' ) is either of the two orifices of the nose A nose is a protuberance in vertebrates that houses the nostrils, or nares, which receive and expel air for Respiration (physiology), respiration alongside ...
s and the
pharynx The pharynx (plural: pharynges) is the part of the throat behind the human mouth, mouth and nasal cavity, and above the esophagus and trachea – the tubes going down to the stomach and the lungs. It is found in vertebrates and invertebrates, thou ...

pharynx
) are quite narrow, firstly by being divided in two by the
nasal septum The nasal septum () separates the left and right airways of the nasal cavity, dividing the two nostrils. It is depressed by the depressor septi nasi muscle. Structure The fleshy external end of the nasal septum is called the columella ...
, and secondly by
lateral Lateral is a geometric term of location {{unreferenced, date=March 2014 Geometric terms of location describe directions or positions relative to the shape of an object. These terms are used in descriptions of engineering, physics, and other scienc ...
walls that have several longitudinal folds, or shelves, called
nasal concha In anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any in ...
e, thus exposing a large area of nasal mucous membrane to the air as it is inhaled (and exhaled). This causes the inhaled air to take up moisture from the wet
mucus Mucus ( ) is a slippery aqueous secretion produced by, and covering, mucous membrane A mucous membrane or mucosa is a biological membrane, membrane that lines various cavities in the body and covers the surface of internal organs. It consists o ...
, and warmth from the underlying blood vessels, so that the air is very nearly saturated with
water vapor (99.9839 °C) , - , Boiling point The boiling point of a substance is the temperature at which the vapor pressure 280px, The ''pistol test tube'' experiment. The tube contains alcohol and is closed with a piece of cork. By heating th ...
and is at almost body temperature by the time it reaches the
larynx The larynx (), commonly called the voice box, is an organ Organ may refer to: Biology * Organ (anatomy) An organ is a group of Tissue (biology), tissues with similar functions. Plant life and animal life rely on many organs that co-exist ...

larynx
. Part of this moisture and heat is recaptured as the exhaled air moves out over the partially dried-out, cooled mucus in the nasal passages, during breathing out. The sticky mucus also traps much of the particulate matter that is breathed in, preventing it from reaching the lungs.


Lower airways

The anatomy of a typical mammalian respiratory system, below the structures normally listed among the "upper airways" (the nasal cavities, the pharynx, and larynx), is often described as a respiratory tree or tracheobronchial tree (figure on the left). Larger airways give rise to branches that are slightly narrower, but more numerous than the "trunk" airway that gives rise to the branches. The human respiratory tree may consist of, on average, 23 such branchings into progressively smaller airways, while the respiratory tree of the
mouse A mouse, plural mice, is a small mammal Mammals (from Latin language, Latin , 'breast') are a group of vertebrate animals constituting the class (biology), class Mammalia (), and characterized by the presence of mammary glands which ...

mouse
has up to 13 such branchings. Proximal divisions (those closest to the top of the tree, such as the trachea and bronchi) function mainly to transmit air to the lower airways. Later divisions such as the respiratory bronchioles, alveolar ducts and alveoli are specialized for
gas exchange Gas exchange is the physical process by which gases move passively by Diffusion#Diffusion vs. bulk flow, diffusion across a surface. For example, this surface might be the air/water interface of a water body, the surface of a gas bubble in a liquid ...

gas exchange
. The trachea and the first portions of the main bronchi are outside the lungs. The rest of the "tree" branches within the lungs, and ultimately extends to every part of the
lung The lungs are the primary organs An organ is a group of tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A given organ's tissues can be broadly categorized as parenchyma ...

lung
s. The alveoli are the blind-ended terminals of the "tree", meaning that any air that enters them has to exit via the same route it used to enter the alveoli. A system such as this creates dead space, a volume of air that fills the airways (the dead space) at the end of inhalation, and is breathed out, unchanged, during the next exhalation, never having reached the alveoli. Similarly, the dead space is filled with alveolar air at the end of exhalation, and is the first air to breathed back into the alveoli, before any fresh air reaches the alveoli during inhalation. The dead space volume of a typical adult human is about 150 ml.


Gas exchange

The primary purpose of breathing is to refresh air in the alveoli so that
gas exchange Gas exchange is the physical process by which gases move passively by Diffusion#Diffusion vs. bulk flow, diffusion across a surface. For example, this surface might be the air/water interface of a water body, the surface of a gas bubble in a liquid ...

gas exchange
can take place in the blood. The equilibration of the partial pressures of the gases in the alveolar blood and the alveolar air occurs by
diffusion Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration In chemistry Chemistry is the study of the properties and behavior of . It is a that covers ...
. After exhaling, adult human lungs still contain 2.5–3 L of air, their
functional residual capacity Functional residual capacity (FRC) is the volume of air present in the lungs at the end of passive expiration. At FRC, the opposing elastic recoil forces of the lungs and chest wall are in equilibrium and there is no exertion by the thoracic ...
or FRC. On inhalation, only about 350 mL of new, warm, moistened atmospheric air is brought in and is well mixed with the FRC. Consequently, the gas composition of the FRC changes very little during the breathing cycle. This means that the pulmonary, capillary blood always equilibrates with a relatively constant air composition in the lungs and the diffusion rate with arterial blood gases remains equally constant with each breath. Body tissues are therefore not exposed to large swings in oxygen and carbon dioxide tensions in the blood caused by the breathing cycle, and the
peripheral A peripheral or peripheral device is an auxiliary device used to put information into and get information out of the computer. The term peripheral device refers to all hardware components that are attached to a computer and are controlled by the co ...
and
central chemoreceptors Central chemoreceptors of the central nervous system, located on the ventrolateral medullary surface in the vicinity of the exit of the 9th and 10th cranial nerves, are sensitive to the pH of their environment. These act to detect the changes in ...
measure only gradual changes in dissolved gases. Thus the homeostatic control of the breathing rate depends only on the partial pressures of oxygen and carbon dioxide in the arterial blood, which then also maintains a constant pH of the blood.


Control

The rate and depth of breathing is automatically controlled by the
respiratory center The respiratory system (also respiratory apparatus, ventilatory system) is a biological system consisting of specific organs and structures used for gas exchange in animal Animals (also called Metazoa) are multicellular eukaryotic org ...
s that receive information from the
peripheral A peripheral or peripheral device is an auxiliary device used to put information into and get information out of the computer. The term peripheral device refers to all hardware components that are attached to a computer and are controlled by the co ...
and
central chemoreceptors Central chemoreceptors of the central nervous system, located on the ventrolateral medullary surface in the vicinity of the exit of the 9th and 10th cranial nerves, are sensitive to the pH of their environment. These act to detect the changes in ...
. These
chemoreceptor A chemoreceptor, also known as chemosensor, is a specialized sensory receptor Sensory neurons, also known as afferent neurons, are neuron A neuron or nerve cell is an membrane potential#Cell excitability, electrically excitable cell (biology) ...
s continuously monitor the partial pressures of carbon dioxide and oxygen in the arterial blood. The sensors are, firstly, the central chemoreceptors on the surface of the
medulla oblongata The medulla oblongata or simply medulla is a long stem-like structure which makes up the lower part of the brainstem. It is anterior and partially inferior to the cerebellum. It is a cone-shaped neuronal mass responsible for autonomic nervous sy ...

medulla oblongata
of the
brain stem The brainstem (or brain stem) is the posterior stalk-like part of the brain A brain is an organ Organ may refer to: Biology * Organ (anatomy) An organ is a group of Tissue (biology), tissues with similar functions. Plant life and anima ...
which are particularly sensitive to as well as the partial pressure of carbon dioxide in the blood and
cerebrospinal fluid Cerebrospinal fluid (CSF) is a clear, colorless body fluid Body fluids, bodily fluids, or biofluids are liquid A liquid is a nearly incompressible In fluid mechanics or more generally continuum mechanics, incompressible flow (isochor ...
. The second group of sensors measure the partial pressure of oxygen in the arterial blood. Together the latter is known as the peripheral chemoreceptors which are situated in the
aortic The aorta ( ) is the main and largest artery in the human body, originating from the Ventricle (heart), left ventricle of the heart and extending down to the abdomen, where it aortic bifurcation, splits into two smaller arteries (the common ilia ...

aortic
and
carotid bodies The carotid body is a small cluster of chemoreceptor cells, and supporting sustentacular cells. The carotid body is located in the adventitia, in the bifurcation (fork) of the common carotid artery, which runs along both sides of the neck. The ...
. Information from all of these chemoreceptors is conveyed to the
respiratory center The respiratory system (also respiratory apparatus, ventilatory system) is a biological system consisting of specific organs and structures used for gas exchange in animal Animals (also called Metazoa) are multicellular eukaryotic org ...
s in the
pons The pons (Latin for "bridge") is part of the brainstem The brainstem (or brain stem) is the posterior stalk-like part of the brain A brain is an organ Organ may refer to: Biology * Organ (anatomy) An organ is a group of Tissue (bi ...

pons
and
medulla oblongata The medulla oblongata or simply medulla is a long stem-like structure which makes up the lower part of the brainstem. It is anterior and partially inferior to the cerebellum. It is a cone-shaped neuronal mass responsible for autonomic nervous sy ...

medulla oblongata
, which responds to deviations in the partial pressures of carbon dioxide and oxygen in the arterial blood from normal by adjusting the rate and depth of breathing, in such a way as to restore partial pressure of carbon dioxide back to 5.3 kPa (40 mm Hg), the pH to 7.4 and, to a lesser extent, the partial pressure of oxygen to 13 kPa (100 mm Hg). For instance,
exercise Exercise is any bodily activity that enhances or maintains physical fitness Physical fitness is a state of health Health is a state of physical, mental and social well-being Well-being, also known as ''wellness'', ''prudential value ...
increases the production of carbon dioxide by the active muscles. This carbon dioxide diffuses into the venous blood and ultimately raises the partial pressure of carbon dioxide in the arterial blood. This is immediately sensed by the carbon dioxide chemoreceptors on the brain stem. The respiratory centers respond to this information by causing the rate and depth of breathing to increase to such an extent that the partial pressures of carbon dioxide and oxygen in the arterial blood return almost immediately to the same levels as at rest. The respiratory centers communicate with the muscles of breathing via motor nerves, of which the
phrenic nerve The phrenic nerve is a mixed motor/sensory nerve which originates from the Spinal nerve, C3-C5 spinal nerves in the neck. The nerve is important for Respiratory system, breathing because it provides exclusive motor control of the Thoracic diaphrag ...
s, which innervate the diaphragm, are probably the most important. Automatic breathing can be overridden to a limited extent by simple choice, or to facilitate
swimming Swimming is the self-propulsion of a person through water, or other liquid, usually for recreation, sport, exercise, or survival. Locomotion is achieved through coordinated movement of the limbs and the body to achieve hydrodynamic thrust whic ...
,
speech Speech is human vocal communication Communication (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''c ...

speech
,
singing Singing is the act of producing musical sounds with the voice. A person who sings is called a singer or vocalist (in jazz and popular music). Singers perform music (arias, recitatives, songs, etc.) that can be sung accompaniment, with or a cap ...

singing
or other
vocal The human voice consists of sound In physics, sound is a vibration that propagates as an acoustic wave, through a transmission medium such as a gas, liquid or solid. In human physiology and psychology, sound is the ''reception'' of such ...
training. It is impossible to suppress the urge to breathe to the point of hypoxia but training can increase the ability to breath-hold. Conscious breathing practices have been shown to promote relaxation and stress relief but have not been proven to have any other health benefits. Other automatic breathing control reflexes also exist. Submersion, particularly of the face, in cold water, triggers a response called the
diving reflex The diving reflex, also known as the diving response and mammalian diving reflex, is a set of physiological Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology Biology i ...
. This firstly has the result of shutting down the airways against the influx of water. The
metabolic rate Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main purposes of metabolism are: the conversion of the energy in food to energy available to run cell ...
slows right down. This is coupled with intense vasoconstriction of the arteries to the limbs and abdominal viscera. This reserves the oxygen that is in blood and lungs at the beginning of the dive almost exclusively for the heart and the brain. The diving reflex is an often-used response in animals that routinely need to dive, such as penguins, seals and whales. It is also more effective in very young infants and children than in adults.


Composition

Inhaled air is by volume 78%
nitrogen Nitrogen is the chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science ...

nitrogen
, 20.95% oxygen and small amounts of other gases including
argon Argon is a chemical element In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behav ...

argon
, carbon dioxide,
neon Neon is a chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that co ...

neon
,
helium Helium (from el, ἥλιος, helios Helios; Homeric Greek: ), Latinized as Helius; Hyperion and Phaethon are also the names of his father and son respectively. often given the epithets Hyperion ("the one above") and Phaethon ("the shining" ...

helium
, and
hydrogen Hydrogen is the chemical element with the Symbol (chemistry), symbol H and atomic number 1. Hydrogen is the lightest element. At standard temperature and pressure, standard conditions hydrogen is a gas of diatomic molecules having the che ...

hydrogen
. The gas exhaled is 4% to 5% by volume of carbon dioxide, about a 100 fold increase over the inhaled amount. The volume of oxygen is reduced by a small amount, 4% to 5%, compared to the oxygen inhaled. The typical composition is: *5.0–6.3% water vapor *79% nitrogen *13.6–16.0% oxygen *4.0–5.3% carbon dioxide *1% argon *
parts per million In science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific method, builds and Taxonomy (general), organizes knowledge in the form of Testability, testable explanations and predictio ...
(ppm) of
hydrogen Hydrogen is the chemical element with the Symbol (chemistry), symbol H and atomic number 1. Hydrogen is the lightest element. At standard temperature and pressure, standard conditions hydrogen is a gas of diatomic molecules having the che ...

hydrogen
, from the metabolic activity of microorganisms in the large intestine. *ppm of
carbon monoxide Carbon monoxide (chemical formula CO) is a colorless, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom. It is the simplest molecule of the oxocarbon family. In ...

carbon monoxide
from degradation of
heme Heme, or haem, is a precursor Precursor or Precursors may refer to: *Precursor (religion), a forerunner, predecessor ** The Precursor, John the Baptist Science and technology * Precursor (bird), a hypothesized genus of fossil birds that was comp ...

heme
proteins. *1 ppm of
ammonia Ammonia is a chemical compound, compound of nitrogen and hydrogen with the chemical formula, formula NH3. A Binary compounds of hydrogen, stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct ch ...

ammonia
. * Trace many hundreds of
volatile organic compounds Volatile organic compounds (VOC) are organic chemicals , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bond, bonds. Due to carbon's abilit ...

volatile organic compounds
especially
isoprene Isoprene, or 2-methyl-1,3-butadiene, is a common organic compound with the formula CH2=C(CH3)−CH=CH2. In its pure form it is a colorless volatile liquid. Isoprene is an unsaturated hydrocarbon. It is produced by many plants and animals (includi ...

isoprene
and
acetone Acetone, or propanone, is an organic compound , CH4; is among the simplest organic compounds. In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, ...

acetone
. The presence of certain organic compounds indicate disease. In addition to air,
underwater divers Underwater divers Underwater divers are people who take part in underwater diving Action (philosophy), activities – Underwater diving is practiced as part of an occupation, or for recreation, where the practitioner submerges belo ...
practicing
technical diving Technical diving (also referred to as tec diving or tech diving) is scuba diving Scuba diving is a type of underwater diving whereby divers use breathing equipment that is completely independent of a surface air supply. The name "scuba", an ...
may breathe oxygen-rich, oxygen-depleted or helium-rich
breathing gas A breathing gas is a mixture of gaseous chemical elements and compounds used for breathing, respiration. Air is the most common, and only natural, breathing gas. But other mixtures of gases, or pure oxygen, are also used in breathing equipment ...
mixtures. Oxygen and
analgesic An analgesic or painkiller is any member of the group of Pharmaceutical drug, drugs used to achieve analgesia, relief from pain. They are distinct from anesthetics, which temporarily affect, and in some instances completely eliminate, sense, sens ...
gases are sometimes given to patients under medical care. The atmosphere in
space suit A space suit or spacesuit is a garment worn to keep a human alive in the harsh environment of outer space Outer space, commonly shortened to space, is the expanse that exists beyond Earth Earth is the third planet from the Sun ...

space suit
s is pure oxygen. However, this is kept at around 20% of Earthbound atmospheric pressure to regulate the rate of inspiration.


Effects of ambient air pressure


Breathing at altitude

Atmospheric pressure Atmospheric pressure, also known as barometric pressure (after the barometer A barometer is a scientific instrument that is used to measure air pressure Atmospheric pressure, also known as barometric pressure (after the barometer), is the ...
decreases with the height above sea level (altitude) and since the alveoli are open to the outside air through the open airways, the pressure in the lungs also decreases at the same rate with altitude. At altitude, a pressure differential is still required to drive air into and out of the lungs as it is at sea level. The mechanism for breathing at altitude is essentially identical to breathing at sea level but with the following differences: The atmospheric pressure decreases exponentially with altitude, roughly halving with every rise in altitude. The composition of atmospheric air is, however, almost constant below 80 km, as a result of the continuous mixing effect of the weather. The concentration of oxygen in the air (mmols O2 per liter of air) therefore decreases at the same rate as the atmospheric pressure. At sea level, where the
ambient pressure Ambient or Ambiance or Ambience may refer to: Music and sound * Ambience (sound recording)In filmmaking, ambience (also known as atmosphere, atmos, or background) consists of the sounds of a given location or space. It is the opposite of "silence" ...
is about 100 
kPa The pascal (symbol: Pa) is the SI derived unit SI derived units are units of measurement ' Measurement is the number, numerical quantification (science), quantification of the variable and attribute (research), attributes of an object or event ...
, oxygen contributes 21% of the atmosphere and the partial pressure of oxygen () is 21 kPa (i.e. 21% of 100 kPa). At the summit of
Mount Everest Mount Everest (Chinese Chinese can refer to: * Something related to China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the List of countries and dependencies by population, world's ...

Mount Everest
, , where the total atmospheric pressure is 33.7 kPa, oxygen still contributes 21% of the atmosphere but its partial pressure is only 7.1 kPa (i.e. 21% of 33.7 kPa = 7.1 kPa). Therefore, a greater volume of air must be inhaled at altitude than at sea level in order to breathe in the same amount of oxygen in a given period. During inhalation, air is warmed and saturated with
water vapor (99.9839 °C) , - , Boiling point The boiling point of a substance is the temperature at which the vapor pressure 280px, The ''pistol test tube'' experiment. The tube contains alcohol and is closed with a piece of cork. By heating th ...
as it passes through the nose and
pharynx The pharynx (plural: pharynges) is the part of the throat behind the human mouth, mouth and nasal cavity, and above the esophagus and trachea – the tubes going down to the stomach and the lungs. It is found in vertebrates and invertebrates, thou ...

pharynx
before it enters the alveoli. The ''saturated'' vapor pressure of water is dependent only on temperature; at a body core temperature of 37 °C it is 6.3 kPa (47.0 mmHg), regardless of any other influences, including altitude. Consequently, at sea level, the ''tracheal'' air (immediately before the inhaled air enters the alveoli) consists of: water vapor ( = 6.3 kPa), nitrogen ( = 74.0 kPa), oxygen ( = 19.7 kPa) and trace amounts of carbon dioxide and other gases, a total of 100 kPa. In dry air, the at sea level is 21.0 kPa, compared to a of 19.7 kPa in the tracheal air (21% of 00 – 6.3= 19.7 kPa). At the summit of Mount Everest tracheal air has a total pressure of 33.7 kPa, of which 6.3 kPa is water vapor, reducing the in the tracheal air to 5.8 kPa (21% of 3.7 – 6.3= 5.8 kPa), beyond what is accounted for by a reduction of atmospheric pressure alone (7.1 kPa). The
pressure gradientIn atmospheric science, the pressure gradient (typically of air but more generally of any fluid In physics, a fluid is a substance that continually Deformation (mechanics), deforms (flows) under an applied shear stress, or external force. Fluid ...
forcing air into the lungs during inhalation is also reduced by altitude. Doubling the volume of the lungs halves the pressure in the lungs at any altitude. Having the sea level air pressure (100 kPa) results in a pressure gradient of 50 kPa but doing the same at 5500 m, where the atmospheric pressure is 50 kPa, a doubling of the volume of the lungs results in a pressure gradient of the only 25 kPa. In practice, because we breathe in a gentle, cyclical manner that generates pressure gradients of only 2–3 kPa, this has little effect on the actual rate of inflow into the lungs and is easily compensated for by breathing slightly deeper. The lower
viscosity The viscosity of a fluid In physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order of nature, or, ...

viscosity
of air at altitude allows air to flow more easily and this also helps compensate for any loss of pressure gradient. All of the above effects of low atmospheric pressure on breathing are normally accommodated by increasing the respiratory minute volume (the volume of air breathed in — ''or'' out — per minute), and the mechanism for doing this is automatic. The exact increase required is determined by the respiratory gases homeostatic mechanism, which regulates the arterial and . This homeostatic mechanism prioritizes the regulation of the arterial over that of oxygen at sea level. That is to say, at sea level the arterial is maintained at very close to 5.3 kPa (or 40 mmHg) under a wide range of circumstances, at the expense of the arterial , which is allowed to vary within a very wide range of values, before eliciting a corrective ventilatory response. However, when the atmospheric pressure (and therefore the atmospheric ) falls to below 75% of its value at sea level, oxygen
homeostasis In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanis ...
is given priority over carbon dioxide homeostasis. This switch-over occurs at an elevation of about . If this switch occurs relatively abruptly, the hyperventilation at high altitude will cause a severe fall in the arterial with a consequent rise in the pH of the arterial plasma leading to
respiratory alkalosis Respiratory alkalosis is a medical condition in which increased respiration elevates the blood pH beyond the normal range (7.35–7.45) with a concurrent reduction in arterial levels of carbon dioxide Carbon dioxide (chemical formula ) is a col ...
. This is one contributor to
high altitude sickness Altitude sickness, the mildest form being acute mountain sickness (AMS), is the harmful effects of high altitude on humans, effect of high altitude, caused by rapid exposure to low Breathing gas#Partial pressure of oxygen, amounts of oxygen at hig ...
. On the other hand, if the switch to oxygen homeostasis is incomplete, then hypoxia may complicate the clinical picture with potentially fatal results.


Breathing at depth

Pressure increases with the depth of water at the rate of about one
atmosphere An atmosphere (from the greek words ἀτμός ''(atmos)'', meaning 'vapour', and σφαῖρα ''(sphaira)'', meaning 'ball' or 'sphere') is a layer or a set of layers of gases surrounding a planet or other material body, that is held in ...
— slightly more than 100 kPa, or one
bar Bar or BAR may refer to: Food *Bar (establishment) A bar is a long raised narrow table or bench designed for dispensing beer or other alcoholic beverage, alcoholic drinks. They were originally chest high, and a bar, often brass, ran the len ...
, for every 10 meters. Air breathed underwater by divers is at the ambient pressure of the surrounding water and this has a complex range of physiological and biochemical implications. If not properly managed, breathing compressed gasses underwater may lead to several diving disorders which include pulmonary barotrauma,
decompression sickness Decompression sickness (DCS; also known as divers' disease, the bends, aerobullosis, or caisson disease) describes a condition arising from dissolved gases coming out of solution into bubbles inside the body on depressurisation. DCS most common ...
,
nitrogen narcosis Narcosis while diving (also known as nitrogen narcosis, inert gas narcosis, raptures of the deep, Martini effect) is a reversible alteration in consciousness that occurs while diving at depth. It is caused by the anesthetic effect of certain ga ...
, and
oxygen toxicity Oxygen toxicity is a condition resulting from the harmful effects of breathing molecular oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical ele ...
. The effects of breathing gasses under pressure are further complicated by the use of one or more special gas mixtures. Air is provided by a
diving regulator A diving regulator is a pressure regulator that controls the pressure of breathing gas for diving. The most commonly recognised application is to reduce pressurized breathing gas to ambient pressure and deliver it to the diver, but there are als ...
, which reduces the high pressure in a
diving cylinder A diving cylinder or diving gas cylinder is a gas cylinder used to store and transport high pressure gas used in diving operations. This may be breathing gas used with a scuba set, in which case the cylinder may also be referred to as a scuba ...
to the ambient pressure. The breathing performance of regulators is a factor when choosing a suitable regulator for the Scuba diving#Types of diving, type of diving to be undertaken. It is desirable that breathing from a regulator requires low effort even when supplying large amounts of air. It is also recommended that it supplies air smoothly without any sudden changes in resistance while inhaling or exhaling. In the graph, right, note the initial spike in pressure on exhaling to open the exhaust valve and that the initial drop in pressure on inhaling is soon overcome as the Venturi effect designed into the regulator to allow an easy draw of air. Many regulators have an adjustment to change the ease of inhaling so that breathing is effortless.


Respiratory disorders

Abnormal breathing patterns include Kussmaul breathing, Biot's respiration and Cheyne–Stokes respiration. Other breathing disorders include shortness of breath (dyspnea), stridor, apnea, sleep apnea (most commonly obstructive sleep apnea), mouth breathing, and snoring. Many conditions are associated with obstructed airways. Hypopnea refers to overly shallow breathing;
hyperpnea Hyperpnea (forced respiration) is increased volume Volume is the quantity of three-dimensional space enclosed by a closed surface, for example, the space that a substance ( solid, liquid, gas, or plasma) or shape occupies or contains. Volume ...
refers to fast and deep breathing brought on by a demand for more oxygen, as for example by exercise. The terms
hypoventilation Hypoventilation (also known as respiratory depression) occurs when ventilation is inadequate (''hypo'' meaning "below") to perform needed respiratory gas exchange. By definition it causes an increased concentration of carbon dioxide Carbon d ...
and
hyperventilation Hyperventilation occurs when the rate or tidal volume of breathing eliminates more carbon dioxide than the body can produce. This leads to hypocapnia, a reduced concentration of carbon dioxide dissolved in the blood. The body normally attempts ...
also refer to shallow breathing and fast and deep breathing respectively, but under inappropriate circumstances or disease. However, this distinction (between, for instance, hyperpnea and hyperventilation) is not always adhered to, so that these terms are frequently used interchangeably. A range of breath tests can be used to diagnose diseases such as dietary intolerances. A rhinomanometry, rhinomanometer uses acoustic technology to examine the air flow through the nasal passages.


Society and culture

The word "spirit" comes from the Latin ''spiritus'', meaning breath. Historically, breath has often been considered in terms of the concept of life force. The Hebrew Bible refers to God breathing the breath of life into clay to make Adam a living soul (nephesh). It also refers to the breath as returning to God when a mortal dies. The terms spirit, prana, the Polynesian mana, the Hebrew ruach and the psyche (psychology), psyche in psychology are related to the concept of breath. In T'ai chi, aerobic exercise is combined with breathing exercises to strengthen the Thoracic diaphragm, diaphragm muscles, improve posture and make better use of the body's Qi, (energy). Different forms of meditation, and yoga advocate various breathing methods. A form of Buddhist meditation called anapanasati meaning mindfulness of breath was first introduced by Gautama Buddha, Buddha. Breathing disciplines are incorporated into meditation, certain forms of yoga such as pranayama, and the Buteyko method as a treatment for asthma and other conditions. In music, some wind instrument players use a technique called circular breathing. Singing, Singers also rely on Singing#Breath control, breath control. Common cultural expressions related to breathing include: "to catch my breath", "took my breath away", "inspiration", "to expire", "get my breath back".


Breathing and mood

Certain breathing patterns have a tendency to occur with certain moods. Due to this relationship, practitioners of various disciplines consider that they can encourage the occurrence of a particular mood by adopting the breathing pattern that it most commonly occurs in conjunction with. For instance, and perhaps the most common recommendation is that deeper breathing which utilizes the diaphragm and abdomen more can encourage relaxation. Practitioners of different disciplines often interpret the importance of breathing regulation and its perceived influence on mood in different ways. Buddhists may consider that it helps precipitate a sense of inner-peace, holistic healers that it encourages an overall state of health and business advisers that it provides relief from work-based stress.


Breathing and physical exercise

During physical exercise, a deeper breathing pattern is adapted to facilitate greater oxygen absorption. An additional reason for the adoption of a deeper breathing pattern is to strengthen the body's core. During the process of deep breathing, the thoracic diaphragm adopts a lower position in the core and this helps to generate intra-abdominal pressure which strengthens the lumbar spine. Typically, this allows for more powerful physical movements to be performed. As such, it is frequently recommended when lifting heavy weights to take a deep breath or adopt a deeper breathing pattern.


See also

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Further reading

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References


External links

* * {{Authority control Respiration Reflexes Human body Gases Articles containing video clips