How does a bird heart work?

Answer 1

Flight muscles need a lot of oxygen on a regular basis and to get it the blood must be kept moving rapidly around the system. To achieve this birds have, like mammals, evolved a four chambered heart (reptiles have only a three chambered heart). Two of these chambers are basically receiving vessels called atria, into them the blood flows at the end of its journey around the body, or to and from the lungs. The other two chambers, called ventricles, are the pumping power houses that send the blood off on its endless journey again. Thus the blood travels in a figure 8 as in mammals.

The oxygenated blood (red) is pumped out to the various parts of the body by the left ventricle, where after giving up its life fuelling oxygen and collecting the carbon dioxide, it returns, as deoxygenated blood (blue) to the right atrium through three large veins called the caval veins - (left caval, right caval and post caval). From here it is shunted to the right ventricle which pumps it out to the bird's lungs via the pulmonary arch where the carbon dioxide is dumped to be exhaled (breathed out) and a new load of oxygen picked up. This newly reoxygenated (red) blood returns to the left atrium of the heart via four large pulmonary veins. (We mammals only have two pulmonary veins). From here it is shunted to the left ventricle so that the cycle can start all over again. The possession of four pulmonary veins, along with the fact that a bird's heart is generally larger and more muscular per pound (or kilogram) or body weight than ours, explains why a bird's circulatory system is more efficient than ours. The left ventricle in a bird's heart is by far the largest chamber and has to work exceptionally hard in small birds which have hovering flight such as humming birds.