What is the chemical equation for breathing


This article deals with physiological breathing; For information on the breathability of textile fabrics, see Klimastoff.

Under breathing (lat .: Respiratio) In common parlance, the activity of the lungs (ventilation) is understood. In a broader sense, however, one understands by breathing All associated processes, because it is necessary for the oxygen in the air to diffuse through the inner surface of the lungs, be carried on to the tissues and cells with the help of the blood, and the carbon dioxide from cells and tissues to be conveyed via the blood to the lungs and finally exhaled.

In biology, the term is even more comprehensive: All processes from the absorption of a reducible substance (in aerobes this is oxygen, O2), its transport into the target cells, its reduction with the help of the respiratory chain (end product in the case of aerobic respiration: water), the storage of as large a part of the released energy as possible in the form of chemically high-energy biomolecules (mostly ATP) and release (exhalation) of the Carbon dioxide (breakdown product of organic substances) are counted for respiration. In this sense it can be formulated in general terms: The breathing is the oxidation of an energy-rich substance (reductant), for example glucose, with the reduction of an external, electron-accepting substance (oxidant, for example oxygen), whereby a (large) part of the energy released by this redox reaction is chemically stored through the synthesis of high-energy molecules.

The respiratory system is organized in a species-specific manner: mammals, for example, cannot breathe water, fish cannot breathe air. The reason for the latter is that the gill leaflets, which get their spread through the water, dry in the air and stick together, whereby the gas exchange over the very delicate exchange surface comes to a standstill. On the other hand, water penetrating into the alveoli can only be exhaled with difficulty against the effect of gravity due to its high specific weight compared to air, and finally the oxygen content of the water is considerably lower than that of normal air, which leads to asphyxiation.

Inner and outer breathing

In biology, according to anatomical / physiological and biochemical aspects, the outer of the inner Breathing (cellular breathing) differentiated:

Inner breathing

As internal breathing or Cellular respiration those metabolic processes are referred to, which serve the energy gain of the cells. In particular, this means the biochemical processes of the respiratory chain in the inner membrane of the mitochondria, at the end of which ATP is synthesized.

External breathing

File: X-ray video of a female American alligator (Alligator mississippiensis) while breathing - pone.0004497.s009.ogv

External respiration occurs only in aerobes, since anaerobes are not organized as multicellular cells. A distinction is made between the following components, which can also occur in combination.

  • Skin respiration, in which the gas exchange with water or with the earth's atmosphere takes place over the entire surface of the body.
  • The gill breathing, in which the gas exchange with water takes place via thin, blood-supplied skin protuberances, the gills. It occurs in many invertebrates, including terrestrial animals, and in fish.
  • Tracheal breathing through tubular indentations in the skin of the body. It is found in insects, millipedes, and some spiders.
  • The lungs: Oxygen is released from the alveoli to the capillaries and carbon dioxide is released from the capillaries to the alveoli. It occurs, for example, in lung-breathing snails and in amphibians, reptiles, birds and mammals (including humans).
  • Gas exchange between plants during photosynthesis via the stomata.
  • The plastron breathing or "physical gill".
  • The distribution of the gases to the target cells in respiratory fluid (blood or lymph), mostly with oxygen transport vectors (hemoglobin or hemocyanin), partly cellular (erythrocytes).

Gas exchange

Gas exchange is only mentioned in the case of gaseous substrates, i.e. not in the case of iron, nitrate, fumarate or sulfur respiration.

The gas exchange always takes place primarily via diffusion. This is a process in physics in which substances are spatially distributed: from areas with high concentration they spread to areas with lower concentration until, ideally, the same concentration prevails everywhere). The exchange via a boundary layer (in biology: membrane) requires a permeability that is as unhindered as possible for these substances. It is also essential to have as large a membrane surface as possible in order to facilitate the exchange.

In multicellular differentiated organisms, special organs as part of external respiration are often responsible for gas exchange.

Factors that affect gas exchange:

  • Permeability of the membrane for the substances to be exchanged
  • Area of ​​the membrane
  • Membrane thickness (= diffusion path)
  • Temperature influences the speed of the molecules in the substances to be exchanged
  • Difference in concentration in the two spaces separated by the membrane: the greater the difference, the faster the passive gas exchange takes place.

Aerobic and anaerobic breathing

Aerobic respiration has only existed since elemental oxygen has been available in the atmosphere and in water. Its formation goes back to the first photosynthetically active prokaryotes, probably precursors of today's cyanobacteria. Before and in an oxygen-poor environment, only anaerobic breathing can / could take place.

Many organisms are capable of several types of breath. For example Escherichia coli live under anaerobic as well as aerobic conditions. Other organisms only master one type of breathing. Mammals, which also include humans, are obligatory aerobes, so they depend on oxygen to survive.

During the oxidation of high-energy compounds (inorganic substances or organic substances such as glucose), electrons are released in a bound form. These are finally transferred to a terminal electron acceptor (respiratory chain) through a usually long chain of redox reactions, from which energy is diverted to form ATP. In aerobic respiration, the latter is always oxygen; in anaerobic respiration, various organic and inorganic substances occur as electron acceptors.

Aerobic breathing

Aerobic respiration requires oxygen. As a rule, organic compounds such as carbohydrates or fatty acids are oxidized and finally reduced to O in a respiratory chain2 transferred as a terminal electron acceptor. When glucose is used as a substrate, aerobic respiration produces carbon dioxide and water. The redox potential E0' is 0.82 V. The sum equation is:

$ \ mathrm {C_6H_ {12} O_6 + 6 \ O_2 \ longrightarrow 6 \ CO_2 + 6 \ H_2O} $
One molecule of glucose and six molecules of oxygen become six molecules of carbon dioxide and six molecules of water

In addition to carbohydrates, microorganisms can also oxidize inorganic substances. For example, B. Acidianus ambivalensSulfur in a sulfur oxidation according to:[1]

$ \ mathrm {2 \ S + 3 \ O_2 + 3 \ H_2O \ longrightarrow 2 \ HSO_4 ^ - + H ^ +} $

The oxidation of ammonium (NH4+) has been observed in some archaea. This aerobic respiration turns ammonium into nitrite (NO2) oxidized:

$ \ mathrm {2 \ NH_4 ^ + + O_2 \ longrightarrow 2 \ NO_2 ^ - + H_2O + H ^ +} $

Anaerobic breathing

In anaerobic respiration, which is only operated by prokaryotes, the electrons obtained from the oxidation of an energy carrier are transferred to other external, reducible substrates instead of oxygen. This must not be confused with forms of fermentation in which the electrons are transferred to metabolic end products and thus the possibility of electron transport phosphorylation does not exist.

The various anaerobic respiratory systems are classified based on the "breathed in" substrate or the metabolic end products.

Only a selection of anaerobic breathing types has been included in the table (see main article for more):

Breathing type Organisms "Substantial" response
aerobic breathing obligatory and facultative aerobes (e.g. eukaryotes) O2 → H2O
Iron breathing facultative aerobes, obligate anaerobes (e.g. Desulfuromonadales) Fe3+ → Fe2+
Nitrate breathing facultative aerobics (e.g. Paracoccus denitrificans, E. coli) NO3- → NO2-
Fumarate breathing facultative aerobics (e.g. Escherichia coli) Fumarate → succinate
Sulphate respiration obligatory anaerobes (e.g. Desulfobacter latus) SO42- → HS-
Thiosulfate breathing z. B. Ferroglobe H2S.2O3 → 2 H2S.
Methanogenesis (carbonate respiration) methanogenic and obligate anaerobes (e.g. Methanothrix thermophila) CO2 → CH4
Sulfur breathing facultative aerobes and obligate anaerobes (e.g. Desulfuromonadales) S.0 → HS-
Inhalation of arsenate Pyrobaculum AsO42− → AsO3
Acetogenesis (carbonate breathing) homoacetogenic and obligate anaerobes (e.g. Acetobacterium woodii) CO2 → CH4

Pulmonary breathing of vertebrates

respiratory tract

The human respiratory system

When you breathe, air flows into your body through your mouth or nose. When inhaling through the nose, the air is first cleaned, moistened and warmed up by the hairs of the nose and mucous membranes. The breath then passes through the pharynx, past the larynx and vocal folds, into the windpipe. The trachea branches into the two branches of the bronchi, which branch out further and further as bronchioles. In the windpipe, the air is cleaned again by tiny cilia. At the end of the day, the alveoli are located in the lungs, through whose thin membrane oxygen passes into the blood vessels and, conversely, carbon dioxide is released from the blood to the lungs.

Breathing Mechanics of Mammals

The two lungs fill the paired pleural cavity in the chest with a narrow gap. This increases by straightening the ribs (chest breathing) and pulling down the muscular diaphragm (abdominal breathing). Since the pleural space, which is filled with fluid, does not change its volume, the lungs must follow this expansion and fill with air via the airways. The alveoli expand against the surface tension. A soap-like liquid (surfactant) reduces this surface tension, on the one hand to relieve the respiratory muscles and on the other hand to avoid the collapse of the smaller bubbles. At the same time, elastic fibers prevent overstretching of already stretched bubbles (for instability in connection with surface tension, see Young-Laplace equation). The regulation of the bronchiolar diameter also contributes to the even ventilation of different parts of the lungs.

As you exhale, the breathing muscles relax and the lungs contract. The pressure in the pleural space usually remains slightly negative. The expiratory auxiliary muscles are only used for forced exhalation during physical exertion, when speaking, singing, coughing or when breathing is difficult.

Breath control in mammals

Breathing is controlled by the brain or the respiratory center in the elongated spinal cord. The decisive factor here is the reaction of chemoreceptors to the carbon dioxide content of the blood. If this exceeds a certain threshold value, the breathing stimulus sets in. Receptors that react to the pH value of the arterial blood and a lack of oxygen are of secondary importance as respiratory stimuli.

The expansion of the lungs is also recorded via the sensitive fibers of the vagus nerve. If this exceeds a certain level, the respiration is limited by reflex.

Measurements in humans

Respiratory rate

The average number of inhalations and exhalations per unit of time (the respiratory rate f) is under rest conditions

Age Breaths per minute
School child
small child

Tidal volume

The tidal volume in an adult is about 0.5 liters at rest.[2]

Minute ventilation

The respiratory minute volume $ V _ {\ rm {Min}} $ is the sum of the tidal volumes $ V _ {\ rm {train}} $ within one minute, the number of which is equal to the product of the respiratory rate f per minute, so:

$ V _ {\ rm {Min}} = V _ {\ rm {Train}} \ cdot f _ {\ rm {Min}} $

Or understood as a rate:

$ \ dot V = f _ {\ rm {Min}} \ cdot V _ {\ rm {Zug}} $

Example: 4200ml / min = 12 / min x 350ml

Dead space

The dead space volume $ V_ {tot} $ is the amount of air that is not actively involved in the gas exchange, ie that "remains" during breathing in the gas-conducting system (space between the mouth and alveoli). When an adult breathes around 500 ml at rest, the dead space corresponds to around 30% of the total tidal volume. In an adult, the dead space volume is around 150-200 ml.

Breath pressure

The adult breath pressure is normally around 50 mbar, with a maximum of around 160 mbar.

Pathological forms of breathing

Classification according to ICD-10
R06 Breathing disorders
R06.1 Stridor
R06.2 Pulling breathing
R06.3 Periodic breathing
R06.4 Hyperventilation
R06.5 Mouth breathing
R06.6 Singultus
R06.7 Sneeze
R06.8 Other and unspecified breathing disorders
ICD-10 online (WHO version 2013)

Breathing disorders (pathological forms of breathing) are listed in the ICD-10 under the Symptoms affecting the circulatory and respiratory systems as R06 summarized. (The following examples serve initially only as a working basis!)

(Signs of central respiratory disorder; breathing typical of brain injury (traumatic brain injury, affected: brain stem), increased intracranial pressure or meningitis)

(Signs of central respiratory disorder; breathing typical of brain injury (e.g. traumatic brain injury, affected: cerebrum))

  • Hyperventilation; exclusive psychogenic hyperventilation!
  • Kussmaul breathing (typical of diabetic ketoacidosis; this leads to hyperventilation)
  • Mouth breathing, snoring
  • Obstructive Sleep Apnea Syndrome
  • Sigh breathing
  • Gasping
  • Hiccup; exclusive psychogenic singultus
  • Stridor

Respiratory therapy

Clinical respiratory therapy deals with diseases and dysfunctions of the lungs and vocal apparatus.

Composition of the exhaled and inhaled air

See also

 Wiktionary: breathing - Explanations of meanings, word origins, synonyms, translations
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  • Lexicon of Biology. Volume 2, Spektrum Akademischer Verlag, Heidelberg, 2004. ISBN 3-8274-0327-8

Individual evidence

  1. ↑ Imke Schröder and Simon de Vries: Respiratory Pathways in Archaea. In: Paul Blum (Ed): Archaea: New Models for Prokaryotic Biology. Caister Academic Press 2008; ISBN 978-1-904455-27-1; P. 2f.
  2. ^ Fisiologia Medica Vol. 2, Fiorenzo Conti, Edi-Ermes
  3. ↑ without water vapor, calculated from: Silbernagl, Despopoulos: Pocket Atlas of Physiology. 6th corrected edition, 2003. p. 107

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