Gills

Gills

Gills are specialized respiratory organs found in many aquatic organisms, primarily fish and some amphibians, that enable them to extract dissolved oxygen from water and expel carbon dioxide. These highly efficient structures consist of a series of thin, feathery filaments arranged in rows on either side of the pharynx. Each filament is richly supplied with blood vessels, allowing for a countercurrent exchange system that maximizes the diffusion of gases between the water and the bloodstream. As water flows over the gills, oxygen diffuses across the thin epithelial membrane of the filaments and into the blood, while carbon dioxide simultaneously diffuses out of the blood and into the water. The efficiency of this gas exchange is further enhanced by the large surface area provided by the numerous gill filaments and the constant flow of water across them, which is typically facilitated by the opening and closing of the mouth and operculum. Gills are vital adaptations that have allowed fish and other aquatic organisms to thrive in a wide range of aquatic environments, from shallow freshwater streams to the depths of the ocean.

aquatic respiration, countercurrent exchange, dissolved oxygen, gas diffusion, gill filaments, operculum, pharynx

— John Armstrong