Crocodiles, ancient predators, possess a uniquely adapted heart. This organ, while sharing characteristics with mammalian hearts, features adaptations that distinguish it from nearly all other vertebrates. Its specialized design allows these creatures to thrive in diverse aquatic and terrestrial environments. The crocodile heart’s complex architecture plays a central role in their survival strategies.
Unique Heart Structure
Crocodiles possess a four-chambered heart, a characteristic shared with birds and mammals, which separates oxygenated and deoxygenated blood. Despite this similarity, their heart features distinct structural differences. One notable deviation is the presence of two aortas. The right aorta originates from the left ventricle, carrying oxygenated blood to the body. Conversely, the left aorta emerges from the right ventricle, positioned alongside the pulmonary artery.
Another unique anatomical feature is the Foramen of Panizza, a small aperture connecting the left and right aortas immediately outside the heart, at their base. This opening allows for communication between the two major systemic arteries. The right ventricle also contains specialized “cog-teeth-like valves” within its pulmonary outflow tract. These structures are composed of connective tissue and can actively influence blood flow dynamics.
Blood Shunting Mechanism
The unique anatomical features of the crocodile heart facilitate a dynamic process of blood shunting, where blood flow can be actively redirected. This is a controlled physiological adjustment, involving specialized muscular valves and pressure gradients. The primary form of shunting is the right-to-left shunt, where deoxygenated blood from the right ventricle bypasses the lungs and enters the systemic circulation.
During a right-to-left shunt, the “cog-teeth-like valves” located in the pulmonary artery constrict, increasing pressure within the right ventricle. This elevated pressure forces deoxygenated blood from the right ventricle into the left aorta, which, unlike in mammals, originates from this chamber. The Foramen of Panizza then allows some deoxygenated blood from the left aorta to mix with oxygenated blood in the right aorta, distributing it throughout the body. A less common left-to-right shunt can also occur, where oxygenated blood from the right aorta flows into the left aorta through the Foramen of Panizza, potentially aiding in the heart’s own oxygen supply. The vagal nerve system controls this shunting by regulating resistance in the pulmonary artery.
Adaptive Advantages
The blood shunting mechanism provides crocodiles with adaptive advantages. One benefit is the ability to undertake prolonged dives. By redirecting blood flow away from the lungs, crocodiles conserve oxygen when submerged, extending their underwater duration for hours. This circulatory adjustment allows them to remain hidden or pursue prey underwater for extended periods.
Shunting also plays a role in the crocodile’s digestive process, particularly after consuming large meals. The mechanism diverts deoxygenated blood, rich in carbon dioxide (CO2), directly to the stomach and other digestive organs. This high CO2 concentration is thought to stimulate the production of exceptionally strong gastric acid, up to ten times more potent than that found in mammals. This powerful acid enables crocodiles to efficiently break down tough prey, including bones.