Mechanism of a Crocodile s Circulatory System Figure 1. A crocodile diving at Botswana (Nachoum, A. 2017) Ever wonder in one of those animal documentaries we watch in television, wherein a crocodile glides carefully under the water, waiting for hours for the perfect time to pounce and snatch their prey and eat it in the water? Like how do these animals manage to stay underwater for almost an hour without surfacing for air, well in fact, they are just like human beings and other animals in the land that are dependent on pulmonary circulation and are in need of the oxygen in the air? According to Kardong, K. (2009), the hearts of crocodiles are structurally similar to some reptiles. The conus arteriosus is the one responsible for the bases of the trunks of the three departing arteries pulmonary and left and right aortic trunks. But according to Bekdemir, M. (2013), crocodiles possess a special heart anatomy different to other reptiles such as the lizards, tortoises, and snakes. These other reptiles are designed to contain three sections including two atriums and one ventricle wherein the deoxygenated blood is collected by the right atrium and the oxygenated blood is collected by the left
atrium retrieved from the pulmonary arteries of the lung and eventually transports the blood to one common ventricle. Since there is only one ventricle to receive and combine oxygenated and deoxygenated blood, a mixture of a less oxygenated blood is pumped to their body resulting to a decrease or an increase body temperature depending on the outside temperature. This causes the metabolism to slow down, while their body temperature decreases when outside temperature as soon near or beyond freezing conditions. This results to hibernation. Just as frogs, they stop hibernating as soon as their body temperature increases depending on the outside temperature when the weather gets warm. Because of this feature, these animals are called cold blooded animals. Warm blooded vertebrates such as the birds and the mammals have a four chamber heart. They have faster metabolic speeds and higher blood pressures. In order that they can function more efficiently, they have various mechanisms to ensure that their body temperature is constantly fair (Steane, R.) For these organisms they can only supply the energy they consume during their daily activities relative to such a fast metabolism and a high level of oxygen provided with oxygenated blood. Imagine if crocodiles have fast metabolisms just as the mammals, and to think that crocodiles do not have much predators, possibly it would lead to some extinctions of species by overpopulating. The low ratio of heart body mass in crocodiles cause its movements to be relatively slower. So in my opinion, God really designed our planet very well, everything with His wisdom, lowers the blood oxygen ratio and the metabolic speed of crocodiles by creating a valve that combines its two aortas. Therefore, eliminating the possibility of crocodile overpopulation. But in relation to that, we, human beings must not
abuse the opportunity that God has bestowed to us by exercising dominion over these poor reptiles because now a days, crocodile skin is now used in the production of bags and shoes causing the extinction of some crocodile species. A crocodilian heart (Figure 2) is different to other reptiles because it has four chambers just like birds and mammals. According to Bekdemir, M. (2013), Blood is sent to the lungs for gas exchange from the right and from the left ventricle it is pumped to the body. Thus the two types of blood do not mix in the heart. However, what is interesting is that blood is mixed as soon as it leaves the heart via a valve (foramen of panizza) placed in between the right and left aorta. Thus the purpose of the blood that is mixed through the medium of a hole is understood after some research that the hole in fact is a necessity for a metabolism suited perfectly to the lifestyle of the crocodile. Figure 2. Blood circulation in reptilian hearts (Frain, P. 2014) According to Kardong, K. (2009), The ventricle is divided by an anatomically complete interventricular septum into distinct left and right chambers. The pulmonary trunk and
left aortic arch open off the thick-walled right ventricle. The right aortic arch opens off the left ventricle. A narrow channel called the foramen of Panizza connects the left and right aortic arches shortly after they depart from the ventricle. Whenever a crocodile breathes air, its right and left atria fills with deoxygenated systemic and oxygenated pulmonary blood. The atria contracts and as it contracts, it delivers blood to its respective ventricles. As the ventricle contracts, blood flows through the nearest portals of least resistance. At the moment of systole, the left ventricle has the greatest pressure. The oxygenated blood that the left ventricle holds will eventually enter the base of the right aortic arch. But because of its high pressure, it also enters the left aortic arch via the foramen of Panizza. The left aortic arch keeps the lunar valves at its base closed because of high pressure, leaving only the pulmonary route of exit for blood in the right ventricle resulting into both aortic arches carry oxygenated blood to systemic tissues, and the pulmonary artery carries deoxygenated blood to the lungs (Kardong, K. 2009) Whenever a crocodile submerge into the water, the opening of its foramen of Panizza narrows with the help of signals coming from the nostrils when crocodiles submerge. Serrated valves at the tip of pulmonary artery that transports the blood to the lungs also constrict at the same time. Since the serrated valve is working, a majority of the blood returning from the body is not sent to the lungs because they are not functioning at the same time. The pressure of the right ventricle is also increased by the serrated valve. This pressure leads to the opening of normal valves at the tip of the left aorta resulting that the left aorta which is responsible in carrying the oxygenated blood starts carrying oxygen deprived blood (Bekdemir, M. 2013).
Whenever a crocodile dives, the pattern of the cardiac blood flow changes because of a cardiac shunt (Kardong, K. 2009). The pulmonary flow resistance increases because of the vasoconstriction of the vascular supply to the lungs and partial constriction of a sphincter at the base of the pulmonary artery. Then a pair of connective tissue valves in the pulmonary outflow closes resulting into a systolic pressure within the right but not the left ventricle will rise substantially, that matches and somewhat exceeds within the left aortic arch. The blood that is in the right ventricle will now tend to exit through the left aortic arch, which shows high resistance to blood flow. A right-to-left cardiac shunt is presented by the diversion of blood in the right ventricle to the systemic circulation. The blood that is in the right ventricle, which would flow to the lungs, instead travels through the left aortic arch that will join the systemic circulation and will bypass the lungs. This is a physiological advantage that the lung bypass confers, namely, an increase in efficiency of blood flow while fresh air is unavailable. Crocodiles are just one of the land animals that can also live in the water and can adapt to its environment with ease and efficiency because of their extra-ordinary mechanisms under water, the change in blood circulation, their slow blood flow, reduced body temperature and metabolic speed. These animals can remain submerged for long periods by their mechanisms. These animals use these mechanisms not only when they are under water, but also while resting or after they are heavily fed. REFERENCES Bekdemir, Mirac (2013). Extraordinary blood circulation in crocodiles.
Retrieved from: http://www.fountainmagazine.com/issue/detail/extraordinaryblood-circulation-in-crocodiles-march-april-2013 Frain, Patrick (2014). Reptiles. Goodridgebiopatrick. Retrieved from: https://goodridgebiopatrick.wordpress.com/2014/03/07/reptiles/ Kardong, Kenneth (2009). Vertebrates, Comparative Anatomy, Function and Evolution Nachoum, Amos (2017). Big Animals Expedition. Retrieved from: http://biganimals.com/wildlife-expeditions/crocodile-diving-2/ Steane, Richard. Warm blooded vertebrates. Retrieved from: http://www.biotopics.co.uk/pot/animals/wbv.html Written by: Ann Dhanica F. Bartolata Contact me at bartolatanica@gmail.com