Trachee (invertebrates)
Tracheae (Singular: trachea or the trachea ) are branched channels for the supply of the tissue of an animal with air . They are characteristic of the arthropods (Arthropoda) and give their name to the Trachea (Tracheata). In the course of evolution , they have probably arisen several times independently from thin areas of skin and have thus supplemented or replaced the exchange of air via the body surface. The openings of the tracheal system located on the body surface are called stigmas (also stigmata , singular: stigma ). The efficiency of breathing through a tracheal system is limited by the rate of diffusion of oxygen, which is one reason for the relatively small size of tracheostomy animals.
Trachea not only take on the gas exchange, but also play the role of the body fluids in vertebrates in the transport of oxygen into the tissue and the removal of carbon dioxide . In addition, the tissues are often fixed on the tracheal system so that it determines their position in the body and thus fulfills part of the role that the skeletal system takes on in vertebrates .
Body fluid with an oxygen transport function (lymph fluid or blood with hemocyanin or hemoglobin ) usually only plays a minor role in the gas supply via trachea, but can be used for fine distribution in the tissue or for oxygen storage in animals living in oxygen-poor waters.
Occurrence and anatomy
Trachea, as invaginations of the skin of the tracheal animals, are lined with a cuticle made of chitin . This is usually only very thin in order to facilitate the absorption of air into the tissue, and often has ring-like or spiral spring-like thickenings ( taenidia , singular: taenidium ) for stabilization . Secondary and tertiary branches can branch off from the main branch of the trachea. The thinnest branches ( tracheoles ) form a fine network on the internal organs and muscles and supply almost every cell in the body. They are usually surrounded by star-shaped tracheal end cells.
Tracheal breathing can be regulated by changing the pressure of the hemolymph , which affects the opening of the trachea. In addition, the ends of the tracheoli can be filled to a greater or lesser extent with fluid.
The active air exchange in the tracheal system, which is not based on diffusion processes alone, even in very small animals, has long been underestimated. Investigations using X-ray phase contrast with synchrotron radiation sources have been able to demonstrate corresponding movements of the trachea inside insect bodies in living animals. In one species of ground beetle, breathing movement through compression and relaxation of the tracheal walls was detected at a frequency of 0.5 Hz , at which one third to one half of the air was exchanged in each case. Autoventilation is of particular importance in many insects. H. Air exchange in the tracheal volume through body movements, for example when running or flying. In the case of larger animals, air ventilation can also be achieved within the system through bellows-like air sacs.
In the trachea, which includes the millipedes (Myriapoda) and the hexapods (Hexapoda) including insects , the tracheas are originally paired in each segment. Often, however, the tracheas of one segment and the tracheas of different segments are connected to one another by transverse and longitudinal canals, so that, for example, in the case of the flying insects (pterygota), a coherent network is created. In addition, air bags can be formed within the system. The stigmas often carry complicated trap systems to prevent foreign objects from entering or to be able to close the system. In animals with fully connected tracheal systems, the spiracles are often reduced to one or two pairs at the front or rear end.
In arachnids, the trachea arise from invaginations or muscle attachments or in one or two pairs in the respiratory cavities of the book lungs . However, many arachnids, especially spiders with well-developed book lungs, have no or only poorly developed tracheas. In columbus (Onychophora), the unbranched trachea arise from spiracles that are irregularly scattered over the body surface. Here the air exchange takes place to a large extent over the body surface.
Arthropods living in water can have trachea to breathe air, whereby the pair of stigmas at the rear end are often used to take in air at the surface of the water. Some larvae of insects living in the water, such as dragonflies or mayflies , develop tracheal gills , in which the tracheal system has no stigmas and takes in air directly from the water via mobile gill systems that are traversed by tracheas.
literature
- Volker Storch , Ulrich Welsch : Short textbook of zoology . 7th edition. Gustav Fischer Verlag, Stuttgart / Jena / New York 1994, ISBN 3-437-20507-2 .
- Neil A. Campbell, Jane B. Reece: Biology . 6th edition. Spectrum Academic Publishing House, Heidelberg / Berlin 2003, ISBN 3-8274-1352-4 .
- G. Czihak, H. Langer, H. Ziegler (Eds.): Biology . Springer, Berlin / Heidelberg / New York 1976, ISBN 3-540-05727-7 .
Web links
Individual evidence
- ↑ Mark W. Westneat, John J. Socha, Wah-Keat Lee: Advances in Biological Structure, Function, and Physiology Using synchrotron X-ray imaging. In: Annual Review of Physiology . 70, 2008, pp. 119-142. doi: 10.1146 / annurev.physiol.70.113006.100434
- ↑ John J. Socha, Wah-Keat Lee, Jon F. Harrison, James S. Waters, Kamel Fezzaa, Mark W. Westneat: Correlated patterns of tracheal compression and convective gas exchange in a carabid beetle. In: Journal of Experimental Biology. 211, 2008, pp. 3409-3420. doi: 10.1242 / jeb.019877