Are leaky heart valves evidence of bad design?
|July 20, 2012||Posted by News under Evolution|
Not if you happen to be an alligator (crocodilian). Doc Gator explains:
Crocodilians have the most complex circulatory system of any vertebrate. It includes a unique anatomical structure called the Foramen of Panizza that allows blood to bypass the lungs while submerged. It was first described in 1833 by Bartolomeo Panizza. When under water, blood pressure in the lungs increases, causing the blood to flow through the Foremen of Panizza and to the systemic circulation without going to the lungs.
The foramen of Panizza functions much like the foramen ovale in unborn mammals by reducing the work load of the heart. Prior to birth, mammals obtain oxygen from the placenta by way of the unbilical cord. At this time it would be of no value for all the blood to go through the lungs. This bypass saves energy and reduces the work load of the heart. The foramen ovale provides a path for blood to flow directly from the right atrium to the left atrium of the heart, bypassing the lungs. With a newborn mammal’s first breath the pulmonary blood pressure decreases and the left atrial pressure exceeds the right atrial pressure closing foramen ovale forcing all the blood to flow to the lungs. Shortly after birth the foramen ovale heals in the closed position as it is no longer needed.
In sharp contrast the foramen of Panizza of crocodilians remains functional throughout their life and helps them occupy their unique ecological niche by allowing them to remain safely submerged sometimes for hours. Many crocodilians also have a special sphincter that prevents blood from flowing in this pathway while they are not diving.
Alligator learns to enjoy a treat: