Gill

Gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water and excretes carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow respiration in air.

Structure and function

Gills are specialized organs containing filaments, which further divide into lamellae. The lamellae contain a dense network of capillaries. Dissolved oxygen in the water diffuses into the blood in the capillaries, and carbon dioxide diffuses out.

Types of gills

Different types of gills exist in different species, and can be categorized into three main types: internal gills, external gills, and cutaneous gills.

Internal gills

Internal gills are enclosed within the body, and water is taken in through the mouth and forced out through the gill slits. Examples of animals with internal gills include fish and some amphibians.

External gills

External gills are exposed to the environment, and are found in many amphibians. They are highly branched structures, and are usually covered by a thin layer of cells which secrete mucus to protect the gills.

Cutaneous gills

Cutaneous gills are found in some species of amphibians, and are extensions of the skin that allow gas exchange. They are usually found in species that have a high metabolic rate, and need a large surface area for gas exchange.

See also

• Respiratory system
• Fish anatomy
• Amphibian

References

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