Invertebrate trachea

Tracheae (singular: trachea or trachea) are branched channels for supplying the tissue of an animal with air. They are characteristic of arthropods ( Arthropoda ) and eponymous for the Tracheentiere ( Tracheata ). In the course of evolution, they are probably arose independently several times from thin skin and have so supplemented or replaced the air exchange through the body surface. The lying on the body surface openings of the tracheal system are called spiracles (also Stigmata, singular: stigma ) refers. The efficiency of the respiration via a tracheal is limited by the diffusion rate of oxygen, which is one reason for the relatively small size tracheenatmender animals.

Tracheae take over not only the exchange of gases, but the transport of oxygen to the tissues and the removal of carbon dioxide and the role that apply the body fluids of vertebrates. In addition, the tissues are at the tracheal often fixed, so that it determines its position in the body and thus fulfills a part of the role that takes the skeletal system in vertebrates.

Body fluid with oxygen transport function ( lymphatic fluid or blood with hemocyanin or hemoglobin) usually plays in the gas supply through tracheae only a minor role, but can be used for the distribution of the tissue or oxygen storage in living in oxygen- poor waters animals.

Occurrence and anatomy

Tracheae are lined as invaginations of the skin of the Tracheentiere of a cuticle made ​​of chitin, which, in order to facilitate the air intake into the tissue, is usually formed only very thin and stabilization often annular or spiral spring-like swellings ( Taenidien, singular: Taenidium ) has. From the main branch of the trachea secondary and tertiary branches can branch off. The thinnest branches ( tracheoles ) form a fine mesh to the internal organs and muscles and cater to almost any cell in the body. They are usually surrounded by star-shaped Tracheenendzellen.

Can be regulated Tracheenatmung the pressure changes of the hemolymph that affect the opening width of the trachea. In addition, the ends of the tracheoles can be more or less filled with liquid.

Been underestimated for a long time is the active exchange of air in the tracheal system that does not rely on diffusion processes even at very small animals alone. Investigations by means of X-ray phase contrast with synchrotron radiation sources have failed to show corresponding movements of the tracheae of insects inside bodies of the living animal. At a beetle species, a respiratory movement was detected by the compression and relaxation of the Tracheenwände with a frequency of 0.5 Hz, in which one-third is replaced up to half of the air. Is of particular importance in many insects car ventilation, ie Air exchange in Tracheenvolumen by body movements, such as running or flying. For larger animals, an air ventilation can also be achieved within the system by bellows- like air sacs functioning.

The Tracheentieren ( Tracheata ) to which the millipedes ( Myriapoda ) and the Hexapod ( Hexapoda ) including include the insects, the tracheae are originally arranged in pairs in each segment. Frequently, however, the trachea of a segment between themselves and the tracheae of different segments are interconnected by transverse and longitudinal channels so that for example the flying insects ( pterygota ) a coherent network is created. In addition, air pockets may be formed within the system. The stigmas often wear complicated Reuse systems to prevent ingress of foreign bodies or to be able to close the system. In animals with fully connected Tracheensystemen the stigmas are often reduced to one or two pairs at the front and / or rear end.

In arachnids (Arachnida ) arise from the trachea to 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, no or only weak development of tracheae on. In Stummelfüßern ( Onychophora ) the unbranched tracheae arise via the body surface irregularly scattered stigmata. Here, the air exchange to a large extent on the surface of the body takes place.

In aquatic arthropod tracheae may have to air breathing, often the Stigmenpaar is used at the back end for receiving breath at the water surface. Some aquatic larvae of insects such as dragonflies or mayflies form of tracheal gills in which the tracheal system has no stigmata and that receives air through gills moving systems that are traversed by tracheae directly from the water.