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The world's smallest known vertebrate, Paedophryne amauensis, sitting on a U.S. dime. The dime is 17.9 mm in diameter, for scale. The word amphibian is derived from the Ancient Greek term ἀμφίβιος (amphíbios), which means 'both kinds of life', ἀμφί meaning 'of both kinds' and βίος meaning 'life'.
The circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the entire body of a human or other vertebrate. [1][2] It includes the cardiovascular system, or vascular system, that consists of the heart and blood vessels (from Greek kardia meaning heart, and from Latin vascula ...
It has a four-chambered heart and two ventricles, an unusual trait among extant reptiles, [80] and both a left and right aorta which are connected by a hole called the Foramen of Panizza. Like birds and mammals, crocodilians have heart valves that direct blood flow in a single direction through the heart chambers.
Modern crocodilians' hearts are 4-chambered, but are smaller relative to body size and run at lower pressure than those of modern birds and mammals. They also have a pulmonary bypass, which makes them functionally 3-chambered when under water, conserving oxygen. a secondary palate, which allows the animal to eat and breathe at the same time.
All lepidosaurs and turtles have a three-chambered heart consisting of two atria, one variably partitioned ventricle, and two aortas that lead to the systemic circulation. The degree of mixing of oxygenated and deoxygenated blood in the three-chambered heart varies depending on the species and physiological state. Under different conditions ...
The octopus has three hearts, one main two-chambered heart charged with sending oxygenated blood to the body and two smaller branchial hearts, one next to each set of gills. The circulatory circuit sends oxygenated blood from the gills to the atrium of the systemic heart, then to its ventricle which pumps this blood to the rest of the body.
Sharks possess a single-circuit circulatory system centered around a two-chambered heart. Blood flows from the heart to the gills where it is oxygenated. This oxygen-rich blood is then carried throughout the body and to the tissues before returning to the heart. As the heart beats, deoxygenated blood enters the sinus venosus.
Fish have what is often described as a two-chambered heart, [43] consisting of one atrium to receive blood and one ventricle to pump it, [44] in contrast to three chambers (two atria, one ventricle) of amphibian and most reptile hearts and four chambers (two atria, two ventricles) of mammal and bird hearts. [43]