Gas exchange

Gas exchange (also called gas exchange ) is a physical process in which gases are spatially redistributed between two compartments (sometimes separated by a permeable membrane , sometimes separated by openings or pores ) . Gas exchange takes place in the context of breathing as the transport of breathing gases between the surrounding external medium ( air , water ) and the metabolizing target cells . The gas exchange can be actively supported by muscle work. In air conditioning , gas exchange is primarily achieved via fans , but the waste heat can also be used in a suitable manner for gas exchange.

Gas exchange is also used when the gases are physically dissolved in liquids (example: absorption of oxygen from water through gills into the blood).

In multicellular differentiated organisms, special organs are often responsible as part of external respiration for gas exchange and its active support. As external respiration doing all those parts of the organism are called, which are responsible for gas exchange and transport between the ambient medium and target cells.

Factors that affect gas exchange

The exchange via a boundary layer (in biology : membrane ) requires a permeability that is as unhindered as possible for these substances ( permeability , usually a semi- permeability ). In addition, in order to facilitate the exchange, it is essential to have as large a membrane surface as possible.

Permeability of the membrane for the gases to be exchanged
Area of the membrane
Membrane thickness (= diffusion path)
Temperature (affects the speed of the molecules of 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.
Respiratory time volume of the organism (active external respiration). When breathing normally at rest, humans inhale around 170 ml of oxygen per liter of air and exhale 130 ml. The proportion of exhaled oxygen increases with higher respiratory time volume and decreases with increased oxygen demand.

Most organisms can increase the gas exchange muscularly (actively) according to their needs, controlled with the help of hormonal and / or nervous stimulation (see: breathing ).

physics

The gas exchange through a membrane always takes place passively via diffusion . The diffusion of gases through an ideally permeable membrane (= opening or pore) takes place along existing partial pressure differences in the direction of an increase in entropy (state variable of thermodynamics ): from areas with high concentration they spread to areas with lower concentration, until ideally the same concentration prevails everywhere.

Pulmonary gas exchange

Gas exchange from an alveolus to the blood

In the physiology of lung breathers, gas exchange essentially means the uptake of oxygen from the alveolar space of the lungs via the alveolocapillary membrane into the blood and tissue and - in the opposite direction - the release of carbon dioxide .

The oxygen transport takes place with a partial pressure decreasing from about 155 to below 5 mmHg from the atmosphere and the inspiratory air via the alveolar air and the arterial blood to the mixed venous blood and from there into the cells. The reverse path is taken by carbon dioxide with a partial pressure of more than 45 mmHg down to zero.

The alveolar gas exchange takes place passively via diffusion processes through the alveolocapillary membrane and the molecular movement in the alveoli.

An optimal gas exchange is present in the alveolus when the ratio of ventilation to perfusion is 0.8. In practice, gas exchange is assessed, among other things, by measuring the arterial oxygen partial pressure.

Web links

Wiktionary: gas exchange - explanations of meanings, word origins, synonyms, translations

Individual evidence

↑ Peter Lotz: Anatomy and Physiology of the Respiratory Tract. In: J. Kilian, H. Benzer, FW Ahnefeld (ed.): Basic principles of ventilation. Springer, Berlin a. a. 1991, ISBN 3-540-53078-9 , 2nd, unchanged edition, ibid 1994, ISBN 3-540-57904-4 , pp. 3–45; here: 30–35.
↑ Hilmar Burchardi: Etiology and pathophysiology of acute respiratory failure (ARI). In: J. Kilian, H. Benzer, FW Ahnefeld (ed.): Basic principles of ventilation. Springer, Berlin a. a. 1991, ISBN 3-540-53078-9 , 2nd, unchanged edition, ibid. 1994, ISBN 3-540-57904-4 , pp. 47-91; here: pp. 60–63.
↑ Thomas Pasch, S. Krayer, HR Brunner: Definition and parameters of acute respiratory insufficiency: ventilation, gas exchange, respiratory mechanics. In: J. Kilian, H. Benzer, FW Ahnefeld (ed.): Basic principles of ventilation. Springer, Berlin a. a. 1991, ISBN 3-540-53078-9 , 2nd, unchanged edition, ibid 1994, ISBN 3-540-57904-4 , pp. 95-108; here: pp. 95–98.

[1] Peter Lotz: Anatomy and Physiology of the Respiratory Tract. In: J. Kilian, H. Benzer, FW Ahnefeld (ed.): Basic principles of ventilation. Springer, Berlin a. a. 1991, ISBN 3-540-53078-9 , 2nd, unchanged edition, ibid 1994, ISBN 3-540-57904-4 , pp. 3–45; here: 30–35.

[2] Hilmar Burchardi: Etiology and pathophysiology of acute respiratory failure (ARI). In: J. Kilian, H. Benzer, FW Ahnefeld (ed.): Basic principles of ventilation. Springer, Berlin a. a. 1991, ISBN 3-540-53078-9 , 2nd, unchanged edition, ibid. 1994, ISBN 3-540-57904-4 , pp. 47-91; here: pp. 60–63.

[3] Thomas Pasch, S. Krayer, HR Brunner: Definition and parameters of acute respiratory insufficiency: ventilation, gas exchange, respiratory mechanics. In: J. Kilian, H. Benzer, FW Ahnefeld (ed.): Basic principles of ventilation. Springer, Berlin a. a. 1991, ISBN 3-540-53078-9 , 2nd, unchanged edition, ibid 1994, ISBN 3-540-57904-4 , pp. 95-108; here: pp. 95–98.