Page "Amphibian" Paragraph 27

Amphibians are cold blooded vertebrates.

Their metabolic rate is low and as a result, their food and energy requirements are limited.

In the adult state they have tear ducts and movable eyelids and most species have ears that can detect airborne or ground vibrations.

They have a muscular tongue which in many species can be protruded.

Modern amphibians have fully ossified vertebrae with articular processes.

Their ribs are usually short and may be fused to the vertebrae.

Their skulls are mostly broad and short and are often incompletely ossified.

Their skin contains little keratin and lacks scales, apart from a few fish-like scales in certain caecilians.

It contains many mucous glands and in some species, poison glands.

The hearts of amphibians have three chambers.

The left and right atria receive oxygenated and de-oxygenated blood respectively.

On contraction, these alternately pass the blood to a single ventricle which pumps it both into both the systemic vessels ( which service the body at large ) as well as the pulmonic vessels ( which return to the lungs for oxygenation ).

The two blood streams remain largely separate in the process.

Amphibians have a urinary bladder and nitrogenous waste products are excreted primarily as urea.

Most amphibians lay their eggs in water and have aquatic larvae that undergo metamorphosis to become terrestrial adults.

Amphibians breathe by means of a pump action in which air is first drawn into the buccopharyngeal region through the nostrils.

These are then closed with valves and the air is forced into the lungs by contraction of the throat.

They supplement this with gas exchange through the skin.