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Respiration

German: Atmung

1 General

By respiration is meant:

  • The external respiration, or the respiratory gas exchange, the intake of oxygen from the environment and the release of carbon dioxide.
  • The internal respiration, a biochemical process in which the organic compounds are oxidized to low-energy substances for the purpose of acquiring ATP.

2 External respiration

2.1 Definition

Higher plants, which also respire, do not possess any special organs for the gas exchange. They absorb atmospheric oxygen through the stomata and distribute it to the individual plant cells through their intercellular system. Animals have developed diverse potentials to receive vital oxygen. One distinguishes:

  • The cutaneous respiration, in which the gas exchange takes place through the entire body surface
  • The gill breathing, in which the gas exchange occurs through fine skin protrusions supplied with blood (gills). They are found in many invertebrates and in fish.
  • The tracheal respiration, which occurs through tubular inversions (spiracles) in the body skin. This type of respiration is found in insects.
  • The lung respiration, in which respiration occurs with the aid of bags (lungs) embedded in the body. This type is found in breathing snails and in amphibians, reptiles, birds and mammals including human beings. See Lungs.

In humans, the term respiration denotes the drawing of breath by the expansion and contraction of the ribcage (chest breathing) and the diaphragm (abdominal breathing). Thereby, the breath is drawn in through the airways into the lungs, where the gas exchange takes place.

2.2 Airways

During respiration, the air is drawn in through the mouth or nose into the body. When respired through the nose, the air is at first cleaned, moistened and warmed by the mucosae and hairs. Subsequently, the air passes along the pharyngeal cavity, larynx and vocal cords to the windpipe (trachea). The windpipe passes on to both branches of the bronchi, which branches out again (bronchioles). At the end, it reaches the alveoli in the lungs, whose fine membranes transfer the oxygen into the capillary vessels and in return releases carbon dioxide from the blood into the lungs. (See also: Respiratory tract)

2.3 Respiratory mechanics

During inhalation (inspiration), the volume of the ribcage increases by the constriction of the chest muscles and the diaphragm. Thereby, the lungs expand causing a low pressure, and air flows into the lungs.
The pleurae (located between the lungs and the ribcage) and the diaphragm respectively allow the lungs to expand with the ribcage. The membrane surrounding the lungs and on the inner side of the ribcage (pleura) as well as on the diaphragm and the pleura parietalis stick to each other like glass plates with a liquid in between. On the one hand, this enables the repositioning of the concerned structures, and on the other, respectively hinders a collapse of the lung during low pressure and enables its expansion. During exhalation (expiration), the lungs constrict again causing high pressure and the air goes out through the airways.

2.4 Respiratory control

The respiration is controlled by the brain and the breathing center in the medulla oblongata. The reaction of the chemo receptors to the carbon dioxide content (and/or carbon dioxide partial pressure) of the blood is the crucial factor. If it rises above a certain threshold value, the stimulus to breathe is initiated. Receptors, which react to the pH value of the arterial blood as well as to the lack of oxygen (hypoxia), have only a secondary significance as a stimulus to breathe.

2.5 Measurement

The breathing rate and the tidal volume serve as measurements of the breathing regulation. The breathing rate, which is the number of the inhalation and exhalation of air, amounts to

  • about 12 per minute in adults
  • about 20 per minute in young people
  • about 30 per minute in small children
  • about 40 per minute in babies.

The tidal volume of a resting adult amounts to between 0.4 and 0.6 liters.

2.6 Pathologic respiratory patterns

The respiratory disorders are summarized as R06 in the ICD 10 under the symptoms pertaining to the circulatory system and the respiratory system. (The following examples serve primarily only as basics!)

3 Internal respiration

Synonym: cellular respiration

Internal respiration is the release of energy from compounds that can metabolize after gaining energy. Thereby the redox equivalents such as NADH or FADH2 emerge, whose energy can be transferred to ATP in another step by oxidation of the inhaled oxygen.

The internal respiration requires the four complexes of the so-called respiratory chain and takes place in the inner membrane of the mitochondria.

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