Gill1 In aquatic organisms
In aquatic organisms, gills are a respiratory organ for the extraction of oxygen from water and for the excretion of carbon dioxide.
Many small aquatic animals absorb oxygen through the surface of their bodies in general, but more complex forms have localized respiratory organs formed to present an adequate surface area to the external environment. They are usually thin plates of tissue or slender tufted processes and, with the exception of some aquatic insects, they contain blood or coelomic fluid which exchange gases through their thin walls. 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, molluscs 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 ( rectumThe 'Rectum' is the final portion of the large intestine in some mammals, and the gut in others, terminating in the anus. Medical procedures For the diagnosis of certain ailments, a rectal exam may be done. Suppositories may be inserted into the rectum as) 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 vertebratePetromyzontidae ( lampreys) Placodermi extinct Chondrichthyes (cartilaginous fish) Acanthodii extinct Actinopterygii (ray-finned fish) Actinistia ( coelacanths) Dipnoi ( lungfish) Amphibia ( amphibians) Reptilia ( reptiles) Aves ( birds) Mammalia ( mammals are developed in the walls of the pharynxThe pharynx is the part of the digestive system of many animals immediately behind the mouth and in front of the esophagus. In mammals, it is where the digestive tract and the respiratory tract cross, commonly called the "throat" (which term may also incl 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 fishAtlantic herring, Clupea harengus one of the most abundant species in the world Photo A fish is a poikilothermic (cold-blooded) water-dwelling vertebrate with gills. There are over 27,000 species of fish, making them the most diverse group of vertebrates. utilize the gills for the excretion of electrolyteAn electrolyte is a substance which dissociates free ions when dissolved (or molten), to produce an electrically conductive medium. Because they generally consist of ions in solution, electrolytes are also known as ionic solutes . They are sometimes refers. In some amphibiansSubclass Labyrinthodontia extinct Subclass Lepospondyli extinct Subclass Lissamphibia Urodela Anura Gymnophiona The class Amphibia consists of all tetrapods (four-legged vertebrates) that do not have amniotic eggs. Amphibians generally spend part of their 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; consequently, 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. Conversely, freshwater is more dilute than the internal fluids of fish, so freshwater fish gain water osmotically through their gills. They eliminate the water through their urine.
