Gjelle

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Ein salamandar som framleis har gjellene

Gjeller i hovudet på ein tunfisk

Gjeller er pusteorgan hjå organismar som lev i vatn. Dei syter for opptak av oksygen frå vatn, og utskilling av karbondioksid.

Mange små vasslevande dyr tek opp oksygen direkte gjennom kroppsoverflata, men meir komplekse former har særskilde organ for å få ei stor nok overflate til å ta opp surstoffet dei treng. Dette er vanlegvis tynne vevplater fylte med blod eller anna væske som slepp gassªr gjennom tynne veggar.

Denne artikkelen er ikkje (ferdig) omsett frå engelsk enno.

Hjelp oss gjerne med å gjera omsetjinga ferdig!

In the insects, a unique type of respiratory organ is used, the tracheal gill, which contains air tubes. The oxygen in these tubes is renewed through the gills.

Gills are developed in sea stars and sea urchins (Echinoidea) as thin protuberances on the surface of the body containing diverticula of the water vascular system. In the crustaceans, mollusks and some insects, they 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 larval dragon fly, the wall of the caudal end of the 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.

Gills of vertebrates are developed in the walls of the pharynx along a series of gill slits opening to the exterior. 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 electrolytes. In some amphibians, the gills occupy the same position on the body but protrude as external tufts. 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. The gill slits of fish are believed to be the evolutionary ancestors of the Eustachian tubes.

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. They eliminate the water through their urine.