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Amphibians: the beginning of the land conquest


Amphibians are not found in the marine environment, only in freshwater and on land environment.

The name of the group, amphibians (from Greek, amphi - on both sides + BIOS = life), was given because most of its representatives had the aquatic larval phase and gill breathing (remember the tadpoles) and an adult phase, lung and skin breathing, which inhabits the humid terrestrial environment. They are heterotherms, like fish.


Tree frog


Salamander


frog


Blind Snake or Cecilia

Gas exchange

Adult amphibians need to live near moisture: their skin is thin and poorly keratinized, very prone to water loss. A thin epidermis with numerous mucous glands makes the skin moist and lubricated, making it an important respiratory organ.

In frogs, the lungs are extremely simple, equivalent to two small-volume, small-surface gas sacs. This feature increases the importance of the skin as a respiratory organ.

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The circulation

The heart has three cavities: two atriums (one right and one left) and a ventricle. Venous blood, poor in O2from the lungs, it enters the left atrium. Both types of blood pass into the single ventricle where they mix, albeit partially. From the ventricle, blood is pumped into an arterial trunk (set of vessels) that distributes blood to the head, trunk and lungs.

THE circulation is double and incomplete: double, because blood passes through the heart twice every cycle of circulation, incomplete, because the ventricle is unique and in it arterial and venous blood mix.

The reproduction

In frogs, frogs and tree frogs, the sexes are separated. Fertilization is external in the aquatic environment. Fertilization occurs, and each egg has a transparent membrane that contains inside it a developing embryo that eats, for its survival, food rich in egg-derived reserves.

After a certain time of development, from each egg emerges a legless larva, the tadpole, containing tail and gills. After a certain lifetime in the water, a series of tadpole modifications begin, which herald the adult phase. Metamorphosis consists of the resorption of the tail and gills and the development of the lungs and four legs.


Stages of Frog Metamorphosis