Gills
Gills
Gills (/ɡɪlz/; from Old Norse gjǫlnar) are the respiratory organs found in many aquatic organisms, which extract dissolved oxygen from water and excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow respiration on land provided they are kept moist. The microscopic structure of a gill presents a large surface area to the external environment.
Anatomy
Gills are made of gill arches. Gill arches are made of gill rakers and gill filaments. The gill filaments are covered with thousands of tiny, thin-walled capillaries, which are the site of gas exchange. The blood in these capillaries flows in the opposite direction to the water, causing counter-current exchange.
Function
Gills use a countercurrent exchange system to extract oxygen from the water, whereby blood flows in the opposite direction to the water. The gills push the oxygen-poor water out through openings in the sides of the pharynx. Some fish have a second set of pharyngeal gills.
In different organisms
Gills are present in various groups of aquatic animals, including fish, amphibians, and many invertebrates. In fish, gills are located on both sides of the pharynx (throat). In most species, gills are highly vascularized (filled with blood vessels) and thin-walled, allowing for gas exchange.
See also
References
External links
- Medical encyclopedia article on Gills
- Wikipedia's article - Gills
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