Gas exchange
Gas exchange is the process of physics at the newly spread gases between two (sometimes by a permeable membrane, sometimes through separate openings or pores ) compartments spatially. Gas exchange takes place as the transport of respiratory gases between the outer surrounding medium ( air, water) and metabolizing the target cells in the respiration. Gas exchange can be actively supported by muscular work. In air conditioning, gas exchange is achieved primarily through fans, but also the waste heat can be adequately used for gas exchange.
From gas exchange is also spoken when it comes to gases that are dissolved in liquids physically (for example, absorption of oxygen from water through gills into the blood ).
In multicellular differentiated organisms specific organs are often responsible as part of the external respiration for gas exchange and its active support. As external respiration doing all those parts of the organism are referred to, which are responsible for gas exchange and transport between the ambient medium and target cells.
Factors influencing the gas exchange
The exchange of a boundary layer ( in biology: membrane) caused an unobstructed for these substances as possible permeability (permeability, usually a semi-permeability ). It is also essential to promote the exchange to have a largest possible diaphragm surface.
- Permeability of the membrane for the gases to be exchanged
- Surface of the membrane
- Membrane thickness ( = diffusion distance )
- Temperature (affects the speed of the molecules of the substances to be replaced )
- Difference in concentration in the two spaces separated by the membrane, the higher the difference, the faster the passive exchange of gas takes place.
- Breathing time volume of the organism ( active external respiration ). In normal breathing at rest by humans per liter of breath approximately 170 ml of oxygen inhaled and exhaled 130 ml again. The proportion of exhaled oxygen increases with increasing respiratory output and decreases with increased oxygen demand.
Most organisms can increase the exchange of gases according to their needs muscular (active), controlled using a hormonal and / or nervous stimulation (see respiration).
Physics
Gas exchange across a membrane is always passively by diffusion. The diffusion of gases through an ideally permeable membrane ( = opening or pore) takes place along existing partial pressure in the direction of increasing entropy ( state size of thermodynamics ): from areas of high concentration they spread to areas of lower concentration until, ideally, everywhere the same concentration prevails.
Pulmonary gas exchange
In medicine and biology of the Lungenatmer with gas exchange substantially the absorption of oxygen from the lungs on alveolar alveolocapillary membrane into the blood and tissue, and - the intended transport of carbon dioxide - in the reverse direction.
The alveolar gas exchange occurs passively by diffusion processes through the alveolocapillary membrane and the molecular motion in the alveoli.