Gill 40579 225787098 2008-07-15T11:55:53Z ClueBot 4928500 Reverting possible vandalism by [[Special:Contributions/Cjdogger2|Cjdogger2]] to version by MattieTK. False positive? [[User:ClueBot/FalsePositives|Report it]]. Thanks, [[User:ClueBot]]. (440758) (Bot) {{Cleanup|date=February 2007}} {{otheruses}} A '''gill''' is an anatomical structure found in many [[aquatic ecosystem|aquatic]] organisms. It is a [[respiration organ]] whose function is the extraction of [[oxygen]] from [[water]] and the excretion of [[carbon dioxide]]. The microscopic structure of a gill is such that it presents a very large [[surface area]] to the external environment. Many microscopic aquatic animals, and those which are somewhat larger but inactive, are able to absorb adequate oxygen through the entire surface of their bodies, and thus they often can respire quite adequately without a gill. However, more complex or more active aquatic organisms usually require a gill or gills. Gills usually consist of thin plates of tissue, branches, or slender tufted [[Process (anatomy)|processes]]. With the exception of some aquatic [[insect]]s, they contain [[blood]] or [[body cavity|coelomic]] fluid, from which gases are exchanged through the thin walls. Oxygen is carried by the blood to other parts of the body. Carbon dioxide passes from the blood through the thin gill tissue into the water. Gills or gill-like organs, located in different parts of the body, are found in various groups of aquatic animals, including [[mollusk]]s, [[crustacean]]s, [[insect]]s, [[fish]], and [[amphibian]]s. == Invertebrate gills == [[Image:Hermit Crab Gills.jpg|thumb|[[Caribbean hermit crab]]s have modified gills to allow them to live in humid conditions]] Respiration in the [[Echinodermata]] (includes [[starfish]] and [[sea urchin]]s) is carried out using a very primitive version of gills called papulli. These are thin protuberances on the surface of the body containing diverticula of the water [[vascular system]]. In [[crustacean]]s, [[mollusk]]s and some insects, gills are tufted or plate-like structures at the surface of the body in which blood circulates. The gills of other insects are of the tracheal kind, and also include both thin plates and tufted structures, and, in the [[larva]]l [[dragon fly]], the wall of the caudal end of the [[Gastrointestinal tract|alimentary tract]] ([[rectum]]) is richly supplied with tracheae as a rectal gill. Water pumped into and out of the rectum provide oxygen to the closed tracheae. In the aquatic insects, a unique type of respiratory organ is used, the [[invertebrate trachea|trachea]]l gill, which contains air tubes. The oxygen in these tubes is renewed through the gills. === Physical gills === '''Physical gills''' are a type of structural adaptation common among some types of aquatic [[insect]]s, in which atmospheric oxygen is held within an area into which the [[spiracle]]s open. The structure (often called a [[plastron]]) typically consists of dense patches of [[hydrophobic]] [[setae]] on the body, which prevent water entry into the spiracles. The physical properties of the interface between the trapped air bubble and the surrounding water function so as to accomplish gas exchange through the spriacles, almost as if the insect were in atmospheric air. [[Carbon dioxide]] diffuses out into the surrounding water due to its high [[solubility]], while [[oxygen]] diffuses into bubbles as the concentration within the bubble has been reduced by [[Respiration (physiology)|respiration]], and nitrogen also diffuses out as its tension has been increased. Oxygen diffuses into the bubble at a higher rate than Nitrogen diffuses out. However, water surrounding the insect can become oxygen-depleted if there is no [[water movement]], so many aquatic insects in still water actively direct a flow of water over their bodies. The physical gill mechanism allows aquatic insects with plastrons to remain constantly submerged. Examples include many [[beetle]]s in the family [[Elmidae]], aquatic [[weevil]]s, and [[true bug]]s in the family [[Aphelocheiridae]]. == Vertebrate gills == [[Image:Tuna Gills in Situ 01.jpg|thumb|The red gills inside a detached [[tuna]] head (viewed from behind)]] Gills of [[vertebrate]]s are developed in the walls of the [[pharynx]] along a series of gill slits opening to the exterior. In fish, the gills are located on both sides of the pharynx. Gills are made of filaments which help increase surface area for oxygen exchange. In bony fish, the gills are covered by a bony cover called an [[operculum (fish)|operculum]]. When a fish breathes, it opens its mouth at regular times and draws in a mouthful of water. It then draws the sides of its throat together, forcing the water through the gill openings. The water passes over the gills on the outside. Valves inside the mouth keep the water from escaping through the mouth again. The operculum can be very important in adjusting the pressure of water inside of the [[pharynx]] to allow proper ventilation of the gills. Lampreys and sharks lack an operculum, they have multiple gill openings. Also, they must use different methods to force water over the gills. In sharks and rays, this ventilation of the gills is achieved either by the use of [[spiracle]]s or ram ventilation (ventilation by constantly swimming). In most species, a [[countercurrent exchange]] system is employed to enhance the diffusion of substances in and out of the gill, with blood and water flowing in opposite directions to each other. Water taken into the mouth passes out of the slits, bathing the gills as it passes. Some [[fish]] utilize the gills for the excretion of [[electrolyte]]s. Gills' large surface area tends to create a problem for fish seeking to regulate the [[osmolarity]] of their internal fluids. Saltwater is less dilute than these internal fluids; as a consequence, saltwater fish lose large quantities of water osmotically through their gills. To regain the water, they drink large amounts of [[seawater]] and excrete the [[salt]]. Freshwater is more dilute than the internal fluids of fish, however, so freshwater fish gain water osmotically through their gills. The gill slits of fish are believed to be the evolutionary ancestors of the [[tonsil]]s, [[thymus gland]], and [[Eustachian tube]]s, as well as many other structures derived from the embryonic [[branchial pouch]]es. In some [[amphibia]]ns, the gills occupy the same position on the body but protrude as external tufts. [[image:Smooth Newt larva (aka).jpg|thumb|An [[Alpine newt]] larva showing the gills, which flare just behind the head]] ===Branchia=== '''Branchia''' (pl. '''branchiæ''') is the name given by the [[Ancient Greek]] naturalists to the gills of [[fish]]. [[Galen]] observed that they are full of little [[foramina]], big enough to admit gases, but too fine to give passage to water. [[Pliny the Elder]] held that fish respired by their gills, but observed that [[Aristotle]] was of another opinion.<ref>{{1728}}</ref> The word ''branchia'' comes from the [[Greek language|Greek]] {{polytonic|βράγχια}}, "gills", plural of {{polytonic|βράγχιον}} (in singular, meaning a [[fin]]).<ref>"Branchia". ''Oxford English Dictionary''. Oxford University Press. 2nd Ed. 1989.</ref> ==References== <references /> ==See also== *[[Aquatic respiration]] *[[Book lung]] *[[Lung]] *[[Artificial gills (human)]] [[Category:Organs]] [[Category:Respiratory system]] [[Category:Fish anatomy]] [[Category:Arthropod anatomy]] [[Category:Animal anatomy]] [[ca:Brànquia]] [[cs:Žábry]] [[da:Gælle]] [[de:Kieme]] [[et:Lõpused]] [[es:Branquia]] [[eo:Branko]] [[fa:آب‌شش]] [[fr:Branchie]] [[hr:Škrge]] [[io:Brankio]] [[it:Branchia]] [[he:זימים]] [[lt:Žiauna]] [[mk:Жабри]] [[nl:Kieuw]] [[ja:えら]] [[no:Gjelle]] [[nn:Gjelle]] [[pl:Skrzela (anatomia)]] [[pt:Brânquia]] [[ru:Жабры]] [[simple:Gill]] [[sr:Шкрге]] [[fi:Kidukset]] [[sv:Gälar]] [[zh:鳃]]