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A spiracle or stigma is the opening in the exoskeletons of insects, myriapods, velvet worms and many arachnids to allow air to enter the trachea. [ 1 ] [ 2 ] [ 3 ] In the respiratory system of insects , the tracheal tubes primarily deliver oxygen directly into the animals' tissues .
The spiracles can be opened and closed in an efficient manner to reduce water loss. This is done by contracting closer muscles surrounding the spiracle. In order to open, the muscle relaxes. The closer muscle is controlled by the central nervous system but can also react to localized chemical stimuli. Several aquatic insects have similar or ...
During the closed phase of discontinuous gas exchange cycles, the spiracle muscles contract, causing the spiracles to shut tight. At the initiation of the closed phase, the partial pressure of both O 2 and CO 2 is close to that of the external environment, but closure of the spiracles drastically reduces the capacity for the exchange of gases with the external environment. [2]
The opposite end of the dorsal tube is like the aorta of the insect circulating the hemolymph, arthropods' fluid analog of blood, inside the body cavity. [1]: 61–65 [53] Air is taken in through openings on the sides of the abdomen called spiracles. There are many different patterns of gas exchange demonstrated by different groups of insects.
Spiracle or spiraculum may refer to: Spiracle (arthropods) , opening in the exoskeletons of some arthropods Spiracle (vertebrates) , openings on the surface of some vertebrates
In this spider diagram, the position of the book lungs is labelled 1. Spider book lungs (cross section) Internal anatomy of a female spider, book lungs shown in pink A book lung is a type of respiration organ used for atmospheric gas-exchange that is present in many arachnids, such as scorpions and spiders.
The spiracle openings may be slits, circular, elliptical or oval according to the species. [58] [59] There are thus four pairs of book lungs; each consists of some 140 to 150 thin lamellae filled with air inside a pulmonary chamber, connected on the ventral side to an atrial chamber which opens into a spiracle. Bristles hold the lamellae apart.
In flies of the order Diptera, the prostigma (also called stigma anteriore or anterior spiracle) is the anterior of the two pairs of spiracles opening on the pleura.The mesothoracic (anterior) pair is located between the pro- and mesothorax and the metathoracic pair (developed mainly in nematocerous Diptera) between the meso- and metathothorax.