Secrets of the 4 chambers revealed by reptile hearts

Published: Wednesday, September 2, 2009 - 16:33 in Biology & Nature

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Embryo hearts show evolution of the heart from 3-chambered in frogs to 4-chambered in mammals.

The first genetic link in the evolution of the heart from three-chambered to four-chambered has been found, illuminating part of the puzzle of how birds and mammals became warm-blooded. Frogs have a three-chambered heart. It consists of two atria and one ventricle. As the right side of a frog's heart receives deoxygenated blood from the body, and the left side receives freshly oxygenated blood from the lungs, the two streams of blood mix together in the ventricle, sending out a concoction that is not fully oxygenated to the rest of the frog's body.

Turtles are a curious transition--they still have three chambers, but a wall, or septum is beginning to form in the single ventricle. This change affords the turtle's body blood that is slightly richer in oxygen than the frog's.

Birds and mammals, however, have a fully septated ventricle--a bona fide four-chambered heart. This configuration ensures the separation of low-pressure circulation to the lungs, and high-pressure pumping into the rest of the body.

As warm-blooded animals, we use a lot of energy and therefore need a great supply of oxygen for our activities. Thanks to our four-chambered heart, we are at an evolutionary advantage: we're able to roam, hunt and hide even in the cold of night, or the chill of winter.




Interestingly, in the turtle, a transitional animal anatomically--with a three-chambered, incompletely septated heart, the molecular signature is transitional as well. A higher concentration of Tbx5 is found on the left side of the heart, gradually dissipating towards the right.


Source: National Science Foundation


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