Graph showing normal as well as different kinds of pathological breathing patterns.
This is a diagram showing how inhalation and exhalation is controlled by a variety of muscles, and what that looks like from a general overall view.
Inhaled air is warmed and moistened by the wet, warm nasal mucosa, which consequently cools and dries. When warm, wet air from the lungs is breathed out through the nose, the cold hygroscopic mucus in the cool and dry nose re-captures some of the warmth and moisture from that exhaled air. In very cold weather the re-captured water may cause a "dripping nose".
Following on from the above diagram, if the exhaled air is breathed out through the mouth on a cold and humid conditions, the water vapor will condense into a visible cloud or mist.
Fig. 4 Atmospheric pressure
Typical breathing effort when breathing through a diving regulator
A young gymnast breathes deeply before performing his exercise.

Process of moving air into and from the lungs to facilitate gas exchange with the internal environment, mostly to flush out carbon dioxide and bring in oxygen.

- Breathing

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The lungs are the primary organs of the respiratory system in humans and most animals including a few fish, and some snails.

Diagram of the human lungs with the respiratory tract visible, and different colours for each lobe
Cross-sectional detail of the lung
Thick elastic fibres from the visceral pleura (outer lining) of lung
TEM image of collagen fibres in a cross sectional slice of mammalian lung tissue.
A lobule of the lung enclosed in septa and supplied by a terminal bronchiole that branches into the respiratory bronchioles. Each respiratory bronchiole supplies the alveoli held in each acinus accompanied by a pulmonary artery branch.
Alveoli and their capillary networks.
3D Medical illustration showing different terminating ends of bronchioles.
The lungs as main part of respiratory tract
3D rendering of a high-resolution CT scan of the thorax. The anterior thoracic wall, the airways and the pulmonary vessels anterior to the root of the lung have been digitally removed in order to visualize the different levels of the pulmonary circulation.
Lungs during development, showing the early branching of the primitive bronchial buds
The effect of the respiratory muscles in expanding the rib cage.
Tissue death of the lung due to a pulmonary embolism
3D still image of constricted airways as in bronchial asthma.
Lung tissue affected by emphysema using H&E stain.
On inhalation, air travels to air sacs near the back of a bird. The air then passes through the lungs to air sacs near the front of the bird, from where the air is exhaled.
The cross-current respiratory gas exchanger in the lungs of birds. Air is forced from the air sacs unidirectionally (from left to right in the diagram) through the parabronchi. The pulmonary capillaries surround the parabronchi in the manner shown (blood flowing from below the parabronchus to above it in the diagram). Blood or air with a high oxygen content is shown in red; oxygen-poor air or blood is shown in various shades of purple-blue.
The axolotl (Ambystoma mexicanum) retains its larval form with gills into adulthood
Book lungs of spider (shown in pink)
thumb|Chest CT (axial lung window)
thumb|Chest CT (coronal lung window)

Mammals, reptiles and birds use their different muscles to support and foster breathing.

Atmosphere of Earth

Layer of gases retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere.

NASA photo showing Earth's atmosphere at sunset, with Earth silhouetted
Composition of Earth's atmosphere by molecular count, excluding water vapor. Lower pie represents trace gases that together compose about 0.0434% of the atmosphere (0.0442% at August 2021 concentrations ). Numbers are mainly from 2000, with and methane from 2019, and do not represent any single source.
Mean atmospheric water vapor
The mole fraction of the main constituents of the Earth's atmosphere as a function of height according to the MSIS-E-90 atmospheric model.
Earth's atmosphere Lower 4 layers of the atmosphere in 3 dimensions as seen diagonally from above the exobase. Layers drawn to scale, objects within the layers are not to scale. Aurorae shown here at the bottom of the thermosphere can actually form at any altitude in this atmospheric layer.
orbiting in the thermosphere. Because of the angle of the photo, it appears to straddle the stratosphere and mesosphere that actually lie more than 250 km below. The orange layer is the troposphere, which gives way to the whitish stratosphere and then the blue mesosphere.
Temperature trends in two thick layers of the atmosphere as measured between January 1979 and December 2005 by microwave sounding units and advanced microwave sounding units on NOAA weather satellites. The instruments record microwaves emitted from oxygen molecules in the atmosphere. Source:
Temperature and mass density against altitude from the NRLMSISE-00 standard atmosphere model (the eight dotted lines in each "decade" are at the eight cubes 8, 27, 64, ..., 729)
Rough plot of Earth's atmospheric transmittance (or opacity) to various wavelengths of electromagnetic radiation, including visible light.
Distortive effect of atmospheric refraction upon the shape of the sun at the horizon.
An idealised view of three pairs of large circulation cells.
Oxygen content of the atmosphere over the last billion years

Within the atmosphere, air suitable for use in photosynthesis by terrestrial plants and breathing of terrestrial animals is found only in Earth's troposphere.


Graph showing normal as well as different kinds of pathological breathing patterns.

Exhalation (or expiration) is the flow of the breath out of an organism.


Compare hypopnea, bradypnea, and hyperventilation.

Graph showing normal as well as different kinds of pathological breathing patterns.

Hypoventilation (also known as respiratory depression) occurs when ventilation is inadequate (hypo meaning "below") to perform needed respiratory gas exchange.


Servo I Ventilator

Hyperventilation occurs when the rate or tidal volume of breathing eliminates more carbon dioxide than the body can produce.

Respiratory rate

Graph showing normal as well as different kinds of pathological breathing patterns.

The respiratory rate is the rate at which breathing occurs; it is set and controlled by the respiratory center of the brain.

Respiratory tract

Subdivision of the respiratory system involved with the process of respiration in mammals.

Conducting passages
Complete respiratory system
Details of upper respiratory tract.
Parts of the lower respiratory tract.
Respiratory epithelium
3D still showing increased mucus.
3D still showing constricted airways.
Differences in cells along the respiratory tract.
Transverse section of tracheal tissue. Note that image is incorrectly labeled "ciliated stratified epithelium" at upper right.

The diaphragm is also the main muscle of respiration involved in breathing, and is controlled by the sympathetic nervous system.

Rib cage

Enclosure that comprises the ribs, vertebral column and sternum in the thorax of most vertebrates, protects vital organs such as the heart, lungs and great vessels.

The human rib cage. (Source: Gray's Anatomy of the Human Body, 20th ed. 1918.)
Human rib cage -CT scan (parallel projection (left) and perspective projection (right))
The four floating ribs indicated
A C7 rib on the right
The effect of the contraction of the accessory muscles of inhalation, pulling the front of the rib cage upwards, a movement known as the 'pump handle movement'. This increases the antero-posterior diameter of the thorax, contributing to the expansion in the volume of the chest. A similar effect, known as the 'bucket handle movement' causes the transverse diameter of the chest to increase, because not only do the ribs slant downwards from the back to the front, but, in the case of the lower ribs, also from the midline downwards to the sides of the chest.
Tyrannosaurus rib cage, University of California Museum of Paleontology
First rib seen from above
Costal groove position on a central rib
Thoracic cage with spine
Anterior surface of sternum and costal cartilages
X-ray image of a human chest, with ribs labelled
Surface projections of the trunk, including each rib, and the costal margin
Thoracic cage with both humerii

The rib cage intrinsically holds the muscles of respiration (diaphragm, intercostal muscles, etc.) that are crucial for active inhalation and forced exhalation, and therefore has a major ventilatory function in the respiratory system.

Medulla oblongata

Long stem-like structure which makes up the lower part of the brainstem.

Medulla oblongata purple, part of the brain stem colored
Medulla oblongata (animation)
Medulla and parts (10-16) - (10) pyramid; (11) the anterior median fissure; (15) is the choroid plexus in the fourth ventricle; (13) olive and (7) the pons
Medulla-animated as it protrudes from the foramen magnum of the skull-base, after which it gives rise to the spinal cord.
Cross section of the medulla (in red) and surrounding tissues.
Anteroinferior view of the medulla oblongata and pons.
Base of brain.
Diagram showing the positions of the three principal subarachnoid cisternæ.
Medulla oblongata
Micrograph of the posterior portion of the open part of the medulla oblongata, showing the fourth ventricle (top of image) and the nuclei of CN XII (medial) and CN X (lateral). H&E-LFB stain.

The medulla contains the cardiac, respiratory, vomiting and vasomotor centers, and therefore deals with the autonomic functions of breathing, heart rate and blood pressure as well as the sleep wake cycle.


Chemical element with the symbol O and atomic number 8.

Joseph Priestley is usually given priority in the discovery.
Antoine Lavoisier discredited the phlogiston theory.
Robert H. Goddard and a liquid oxygen-gasoline rocket
An experiment setup for preparation of oxygen in academic laboratories
Orbital diagram, after Barrett (2002), showing the participating atomic orbitals from each oxygen atom, the molecular orbitals that result from their overlap, and the aufbau filling of the orbitals with the 12 electrons, 6 from each O atom, beginning from the lowest-energy orbitals, and resulting in covalent double-bond character from filled orbitals (and cancellation of the contributions of the pairs of σ and σ* and π and π* orbital pairs).
Liquid oxygen, temporarily suspended in a magnet owing to its paramagnetism
Space-filling model representation of dioxygen (O2) molecule
Oxygen discharge (spectrum) tube
Late in a massive star's life, 16O concentrates in the O-shell, 17O in the H-shell and 18O in the He-shell.
Cold water holds more dissolved.
500 million years of climate change vs. 18O
Photosynthesis splits water to liberate and fixes into sugar in what is called a Calvin cycle.
build-up in Earth's atmosphere: 1) no produced; 2) produced, but absorbed in oceans & seabed rock; 3)  starts to gas out of the oceans, but is absorbed by land surfaces and formation of ozone layer; 4–5)  sinks filled and the gas accumulates
Hofmann electrolysis apparatus used in electrolysis of water.
Oxygen and MAPP gas compressed-gas cylinders with regulators
An oxygen concentrator in an emphysema patient's house
Low pressure pure is used in space suits.
Most commercially produced is used to smelt and/or decarburize iron.
Water is the most familiar oxygen compound.
Oxides, such as iron oxide or rust, form when oxygen combines with other elements.
Main symptoms of oxygen toxicity
The interior of the Apollo 1 Command Module. Pure at higher than normal pressure and a spark led to a fire and the loss of the Apollo 1 crew.

He noted that candles burned brighter in the gas and that a mouse was more active and lived longer while breathing it.